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Electrical stimulation of the cerebellar fastigial nucleus (FN) globally and profoundly increases cerebral blood flow via a cholinergic mechanism. In cerebral cortex, the vasodilation is unassociated with alterations in cerebral glucose utilization, a condition favoring protection against cerebral ischemia. We sought to determine whether FN stimulation would modify the size of the focal ischemic infarction resulting from occlusion of the middle cerebral artery (MCA). The MCA was occluded in anesthetized rats of the spontaneously hypertensive (SHR) or Sprague-Dawley (SD) strains with or without 1 h of electrical stimulation of the FN. Twenty-four hours later, rats were killed and the volume of the infarction established in thionin-stained sections. in SHRs, FN stimulation reduced by 40% the well-established cortical and partially subcortical infarctions elicited by occlusion of the MCA (from 186 +/- 35.2 to 113 +/- 47.1 mm3, mean +/- SD, n = 15; p less than 0.001). The zone of retrieval was anatomically constant, consisting of a rim of cortex dorsal and ventral to the infarction and medially within the thalamus and striatum corresponding to the penumbral zone described by others. The effect was comparable in rats of the SD strain having smaller infarctions. The effect of FN stimulation appears to be selective for the FN system in that it is not evoked by stimulation of the dentate nucleus and is blocked by systemic administration of atropine (1.0 mg/kg). We conclude that excitation of an intrinsic system in brain represented in the rostral FN has the capacity to reduce substantially an ischemic infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

Microinjection of neuropeptide Y (NPY) into the nucleus tractus solitarius (NTS) induces an initial and reversible fall in arterial pressure (AP) and heart rate (HR), along with a delayed and long-lasting blockade of cardiovascular responses to L-glutamate (L-Glu) injected into the same site and an inhibition of the baroreflex arc. By injecting NPY-receptor subtype selective agonists and NPY-related peptides into NTS we have sought to characterize the receptors that mediate these responses. Unilateral injections into NTS (9-90 pmol) of NPY as well as the Y1 receptor selective agonist [34Pro]NPY and the Y2 receptor selective fragment NPY 13-36 evoked comparable dose-dependent falls of AP and HR in the anesthetized and paralyzed rat. Injections into NTS of peptide YY or pancreatic polypeptide had no effect. Preinjection of NPY, [34Pro]NPY, NPY 13-36 (all at 90 pmol) as well as norepinephrine (6.7 nmol) virtually abolished the fall in AP and HR evoked by subsequent injections of L-Glu into NTS. Injection of peptide YY or pancreatic polypeptide (both at 90 pmol) did not affect the cardiovascular responses evoked by L-Glu in NTS. Injection of NPY (90 pmol) into the caudal ventrolateral medulla induced a slight fall in AP of -17 +/- 5 mm Hg (P less than .05) and a sustained fall in HR of -44 +/- 8 beats per min (P less than .01). Injection of NPY also abolished the fall in HR and AP evoked by L-Glu in the caudal ventrolateral medulla. The profile of the cardiovascular effects elicited by the NPY-related peptides in NTS does not correspond to either of the Y1 or the Y2 receptor subtypes. The findings suggest that NPY acts on an atypical receptor in NTS to lower AP and HR. Moreover, this receptor may also interfere with the L-Glu-evoked neurotransmission in the NTS. Finally, norepinephrine shared with NPY the ability to inhibit L-Glu-evoked responses in NTS; however, a much higher dose of norepinephrine (than NPY) was required.

We sought to determine the site of action and receptor type responsible for the antihypertensive actions of rilmenidine, an oxazoline analogue of clonidine. In anesthetized paralyzed rats decerebration did not alter the dose dependent reductions in arterial pressure and heart rate elicited by i.v. drug. Rilmenidine microinjected bilaterally into the C1 area of the rostral ventrolateral medulla (RVL), but not nucleus tractus solitarii (NTS) nor caudal ventrolateral medulla (CVL), elicited dose-dependent falls in arterial pressure and heart rate at doses an order of magnitude less than required systemically. Prior microinjection into the C1 area of the selective alpha 2-adrenoceptor antagonist SKF-86466, even at high doses, failed to modify the hypotension to i.v. rilmenidine. However, microinjection of 3- to 10-fold lower doses of idazoxan, a ligand for imidazole as well as alpha 2-adrenoceptors, blocked the effects. Rilmenidine also competed with the clonidine analogue [3H]p-aminoclonidine ([3H]PAC) at specific binding sites in membranes of bovine ventrolateral medulla and frontal cortex. In RVL rilmenidine competed with binding to imidazole and alpha 2-adrenergic binding sites with a 30-fold selectivity for the imidazole binding sites. In frontal cortex binding was of lower affinity and restricted to alpha 2-adrenergic sites. We conclude that rilmenidine, like clonidine, acts to lower arterial pressure by an action on imidazole receptors in the C1 area of RVL. The higher selectivity of rilmenidine for imidazole to alpha 2-adrenoceptors as compared to clonidine may explain the lower sedative effects of rilmenidine.

Repeated administration of cocaine elicits substantial, long-lasting, but reversible reductions in neuropeptide Y (NPY) and NPY mRNA in the rat cerebral cortex and nucleus accumbens. The NPY reduction appears to be mediated through a decrease in NPY biosynthesis, occurring transneuronally, perhaps in response to changes in synaptic dopamine associated with mesolimbic and mesocortical dopamine neurons. The medial prefrontal cortex appears necessary for maintenance of cocaine's action on this neuronal network since excitotoxic lesions of this area prevented (lesion before cocaine) and reversed (lesion after cocaine) the reductions in NPY elicited by the cocaine. NPY may be a sensitive marker for chronic cocaine use. Its decrease may relate to the anxiety and depression associated with cocaine withdrawal in humans.

Neuropeptide Y (NPY) microinjected unilaterally into the nucleus tractus solitarii (NTS) of anesthetized paralyzed rats elicits a gradual dose-dependent and reversible fall in arterial pressure (AP) and heart rate (HR) lasting 20 min. It also abolished the brief (less than 1 min) dose-dependent and reversible fall of AP and HR elicited by L-glutamate (L-Glu) injected into the nucleus. The blockade of L-Glu by NPY appeared gradually and was prolonged, lasting over 2 h, and recovering by 24 h. It was not replicated by desamido-NPY or galanin. Unlike 2% lidocaine it did not block the hypotension elicited by focal electrical stimulation at the injection site indicating the response was not that of a local anesthetic. Bilateral injection of NPY into the NTS resulted, after an initial fall, in an elevation of AP (+48 +/- 10.6 mmHg). At this time the reflex bradycardia evoked by elevating AP with phenylephrine was markedly reduced. We conclude that in the NTS, NPY antagonizes the actions of L-Glu and may attenuate baroreceptor reflexes. Since the NTS is richly innervated by NPY neurons and contains many NPY binding sites and since primary baroreceptor afferents appear to be glutamatergic the results suggested that NPY may serve in NTS as a long-term regulator of baroreceptor reflex activity.

Suicidal behavior has been linked to a deficiency in serotonin neurotransmission, but it is not known which brain regions are involved. We determined the pattern of alteration in serotonin 5-HT2 (5-HT2) receptor binding sites in suicide victims in prefrontal cortex compared with temporal cortex using a matched-pairs design to study 11 suicide victims and 11 matched controls, by both membrane binding and quantitative receptor autoradiography. Since a relationship between the serotonergic and noradrenergic systems has been proposed, we also examined beta-adrenergic receptor binding sites. Binding to 5-HT2 and beta-adrenergic sites in slide-mounted sections correlated strongly with binding site number in membrane preparations. A specific laminar distribution of 5-HT2 binding sites was found in both the control and suicide groups, whereas beta-adrenergic binding sites did not differ across cortical layers. A significant increase was found in suicide victims across all cortical layers in both receptor subpopulations in the prefrontal cortex, but only beta-adrenergic sites were increased in the temporal cortex. We conclude that suicide is associated with a localized increase in 5-HT2 binding sites.

We sought to determine whether high spatial resolution magnetic resonance imaging is useful for noninvasive quantitation of the ischemic infarct produced by occlusion of the middle cerebral artery and for detection of reduced infarct volume elicited by electric stimulation of the cerebellar fastigial nucleus. Male rats of the spontaneously hypertensive strain were anesthetized, the middle cerebral artery was occluded, and the fastigial nucleus was stimulated for 1 hour. Twenty-four hours later, rats were reanesthetized and T1- and T2-weighted images were obtained. Rats were killed and the volume and distribution of the lesion was established by histopathology. Magnetic resonance imaging estimates of the lesion volume were 271 +/- 41.0 mm3 (middle cerebral artery, n = 5) and 148 +/- 8.4 mm3 (middle cerebral artery + fastigial nucleus stimulation, n = 6; 45% reduction, p less than 0.05). Histopathological analysis revealed a lesion of 229.8 +/- 15.4 mm3 involving somatosensory cortex, lateral caudate putamen, and lateral hippocampus. Fastigial nucleus stimulation resulted in a 36% reduction in infarct volume to 146.0 +/- 10.3 mm3. The retrieved zone was largely in the cortex dorsal and ventral to the lesion and mostly posterior to the lesion. The estimates of lesion volume by magnetic resonance imaging and histopathology did not differ and were highly correlated (r = 0.90; p less than 0.001). This study confirms our previous finding that fastigial nucleus stimulation reduces the volume of a focal ischemic infarct and demonstrates that magnetic resonance imaging not only accurately estimates the volume of the lesion but also can detect changes as small as 50-100 mm3.

Laser-Doppler flowmetry was used to continuously monitor cortical CBF during electrical stimulation of the fastigial nucleus (FN). Rats were anesthetized with isoflurane (0.75-5%), paralyzed, and artificially ventilated. The LDF probe was placed over a target region of the parietal cortex through a burr hole. The hypertension associated with FN stimulation was prevented by spinal cord transection at C1 with arterial pressure maintained by i.v. infusion of phenylephrine. After cord transection, CBF changed linearly with changes in arterial pco2 (r = 0.93; n = 23). FN stimulation (50-100 microA, 50 Hz, 1 s on/1 s off) produced sustained increases in CBF that developed slowly, reaching 50% of maximum within 24 +/- 1 s of stimulation (n = 17). After stimulation, CBF returned to baseline gradually within a time period (84-540 s) proportional to the duration of the stimulation (r = 0.93; n = 15). The CBF response was stimulus frequency and intensity dependent, was elicited only from restricted sites in FN, and was abolished by atropine (1 mg/kg, i.v.) or pentobarbital (30 mg/kg, i.v.). The slow temporal profile of the cerebrovasodilation is compatible with the hypothesis that in cerebral cortex local neurons mediate the vasodilation by interstitial release of vasoactive agents rather than by a direct action of neural processes on blood vessels. LDF is an effective technique for monitoring phasic change in CBF and may be useful in studies of the intrinsic neurogenic control of the cerebral circulation.

While brain injury elicits local cellular proliferation, it is not known whether cells not originating in brain substantially participate in the response. We assessed the time course and phenotype of dividing cells following neuronal damage initiated by microinjection of the neurotoxin ibotenic acid into one caudate nucleus (CN) in adult rat. Proliferation was determined in an in vitro assay measuring incorporation of [3H]thymidine into cellular DNA in cultures of lesioned and uninjected CN. Cellular phenotypes were determined immunocytochemically. Our results show that the proliferative response to brain injury has a rapid onset, peaks within 2 weeks and persists. The majority of proliferating cells that respond to selective neuronal injury are not intrinsic to the central nervous system, but rather are of hematic origin, involving monocytes, macrophages and T-helper lymphocytes.

We sought to characterize regional heterogeneity of astrocytes using adrenergic receptor sites as cellular markers. Primary cultures made from 6 regions of neonatal rat brain consisted almost exclusively of astrocytes. Membranes from astrocytes cultured 1-3 weeks were prepared for radioligand binding assays of beta- and alpha 2-adrenergic sites using the ligands [3H]dihydroalprenolol and [3H]p-aminoclonidine, respectively. Receptor expression was not affected by time in culture. Astrocytes from different brain regions varied up to 3-fold with respect to number but not affinity for both classes of adrenergic binding site with a rank order of cerebral cortex = superior colliculus greater than hippocampus = ventral midbrain greater than or equal to caudate nucleus greater than or equal to hypothalamus. Binding to beta- and alpha 2-adrenergic receptors was positively correlated across brain regions. Astrocytic receptor binding in each region did not correspond to total receptor levels assessed by quantitative autoradiography. We conclude that: (a) astrocytes are markedly heterogeneous between major brain regions with respect to expression of adrenergic binding sites; (b) regional variations in the density of adrenergic binding sites in brain reflect, in part, local specialization of astrocytes; and (c) a substantial proportion of the adrenergic binding sites in some brain regions may be on astrocytes.

Studies using isolated cell membranes have shown that beta-adrenergic receptors exist in two interconvertible conformations, one with high affinity for agonists and the other with low affinity. Guanine nucleotides and sodium shift high-affinity receptor sites into low-affinity sites. We sought to demonstrate affinity states of the beta-adrenergic receptor in slide-mounted sections of rat and human postmortem brain, and to determine using quantitative receptor autoradiography the regional distribution in the brain of high-affinity receptors relative to the total population of beta-adrenergic receptors. The beta-adrenergic agonist isoproterenol inhibited the binding of 125I-iodopindolol to slide-mounted sections of rat forebrain and human premotor cortex in a biphasic manner. Approximately 80% of the beta-receptor sites in both rat and human brain showed high-affinity for isoproterenol (7-14 nM). Treatment with 0.1 mM non-hydrolyzable guanine nucleotide 5'-guanylylimidodiphosphate and 25 mM NaCl abolished high-affinity binding in rat brain sections and reduced it in human brain sections. These findings were confirmed by membrane studies using similar tissue samples. For autoradiographic studies, 17 nM isoproterenol displaced 71% of the high-affinity sites without affecting low-affinity beta-adrenergic receptors. Digital subtraction was used to selectively visualize beta-receptors in the high-affinity conformation. The proportion of beta-adrenergic receptors in the high-affinity conformation differed significantly across rat brain regions and across human cortical layers. We conclude that beta-adrenergic affinity states, presumably reflecting the interaction of the receptor with a G-protein, occur in slide-mounted sections of rat brain and persist in human postmortem material.(ABSTRACT TRUNCATED AT 250 WORDS)

We studied the effects of chloralose anesthesia on the elevation in arterial pressure (AP), heart rate (HR), and regional CBF (rCBF) elicited by stimulation of the cerebellar fastigial nucleus (FN). Rats were anesthetized with an initial dose of chloralose (40 mg/kg s.c.), paralyzed, and artificially ventilated. The FN was stimulated (50-100 microA, 50 Hz, 1 s on/1 s off) with microelectrodes stereotaxically implanted. During the stimulation AP was carefully maintained within cerebrovascular autoregulation. CBF was measured by the [14C]iodoantipyrine technique with regional dissection. In rats that received only the initial dose of chloralose, FN stimulation elevated rCBF in brain and spinal cord, up to 209 +/- 13% of control in frontal cortex (n = 5; p less than 0.01, analysis of variance). Administration of additional chloralose (10 mg/kg i.v., 30 min prior to measurement of CBF) did not affect resting rCBF (n = 5), the EEG, or the elevation in AP and HR elicited by FN stimulation (n = 4). However, the additional chloralose abolished the elevations in rCBF (n = 5; p greater than 0.05). Thus, the cerebrovasodilation elicited from the FN is more susceptible to the effects of additional anesthesia than the elevation in AP and HR. These results indicate that the cerebrovascular and cardiovascular responses elicited from the FN are functionally distinct and provide additional evidence for the notion that these responses are mediated by different neural pathways and transmitters.

The rostral ventrolateral medulla is the primary site of action for clonidine, a centrally acting antihypertensive. In the rostral ventrolateral medulla, clonidine binds not only to alpha-2 adrenergic receptors but also to specific imidazole sites. In order to determine whether a putative imidazole receptor mediates the hypotensive action of clonidine, a series of compounds was tested 1) in vitro for binding affinity at imidazole and alpha-2 sites and 2) in vivo for ability to lower arterial pressure and heart rate when microinjected directly into the rostral ventrolateral medulla. Hypotensive potency was correlated with affinity at imidazole sites (r = 0.84), but not with alpha-2 affinity (r = -0.05). The bradycardia elicited by this series of compounds also correlated with affinity at imidazole receptors (r = 0.89), but not with alpha-2 affinity (r = 0.10). Furthermore, the imidazole idazoxan selectively reversed the fall in arterial pressure elicited by clonidine, whereas SKF-86466, an alpha-2 antagonist which is not an imidazole, failed to attenuate clonidine's action. An imidazole receptor in the rostral ventrolateral medulla appears to mediate the central hypotensive actions of clonidine and related centrally acting imidazoles and may participate in the regulation of arterial pressure and heart rate.

This study sought to determine whether release of acetylcholine (ACh) within the C1 area of nucleus reticularis rostroventrolateralis (RVL) contributes to the tonic maintenance of arterial pressure (AP) in the rat. The activity of choline acetyltransferase (ChAT), the biosynthetic enzyme for ACh, varied 5.5-fold in micropunches of the 6 medullary regions examined. ChAT activity in the C1 area (179 +/- 35 nmol [14C]ACh formed/mg protein/60 min; n = 4) was intermediate between that of the hypoglossal nucleus (249 +/- 38; highest) and the pyramids (45 +/- 11; lowest) and equivalent to that found in the parietal cortex (147 +/- 15). Release of [3H]ACh from C1 area micropunches was increased by raising extracellular K+ concentrations (5-55 mM) and was entirely Ca2(+)-dependent. Muscarinic receptor binding density was assessed using [3H]quinuclidinyl benzylate ([3H]QNB) as ligand and a recently developed 'electronic micropunch' technique which allows measurement of quench-corrected [3H]QNB binding within corresponding cylinders of tissue obtained by the mechanical micropunch cannula. [3H]QNB binding density varied 2.6-fold: lateral reticular nucleus pars lateralis greater than C1 area greater than nucleus ambiguus = hypoglossal nucleus = pyramid = oral spinal trigeminal nucleus. In urethane-anesthetized rats, inhibition of ACh synthesis by hemicholinium-3 (HC-3, 3 nmol/50 nl), or blockade of muscarinic receptors by scopolamine (SCOP, 3 nmol/50 nl), reduced resting mean AP by 18-24 mm Hg following bilateral microinjection into the C1 area. These concentrations of HC-3 and SCOP were sufficient to attenuate by 70-80% the increase in local cholinergic neurotransmission elicited by the cholinesterase inhibitor physostigmine given systemically. High concentrations of SCOP (30-150 nmol/50 nl) lowered AP by 46-60 mm Hg. Similarly, bilateral microinjections of GABA (10 nmol/50 nl) into the C1 area markedly reduced mean AP by 51 +/- 6 mm Hg to levels normally found after transection of the spinal cord. Thus, a substantial portion of tonic sympathetic activity may be driven by activation of muscarinic receptors in the C1 area. In the spontaneously hypertensive rat (SHR), a genetic model of hypertension, neither spontaneous nor K(+)-evoked release of [3H]ACh from the C1 area differed from that of normotensive Wistar-Kyoto rats (WKY).(ABSTRACT TRUNCATED AT 400 WORDS)

Unlabelled: Acetylcholine (ACh) plays a major role in central autonomic regulation, including the control of arterial blood pressure (AP). Previously unknown neuroanatomic substrates of cholinergic-autonomic control were mapped in this study. Cholinergic perikarya and bouton-like varicosities were localized by an immunocytochemical method employing a monoclonal antiserum against choline acetyltransferase (ChAT), the enzyme synthesizing ACh. In the forebrain, bouton-like varicosities and/or perikarya were detected in the septum, bed nucleus of the stria terminalis, amygdala (in particular, autonomic projection areas AP1 and AP2 bordering the central subnucleus), hypothalamus (rostrolateral/innominata transitional area, perifornical, dorsal, incertal, caudolateral, posterior [PHN], subparafascicular, supramammillary and mammillary nuclei). Few or no punctate varicosities were labeled in the paraventricular (PVN) or supraoptic (SON) hypothalamic nuclei. In the mid- and hindbrain, immunoreactive cells and processes were present in the nucleus of Edinger-Westphal, periaqueductal gray, parabrachial complex (PBC), a periceruleal zone avoiding the locus ceruleus (LC), pontine micturition field, pontomedullary raphe, paramedian reticular formation and periventricular gray, A5 area, lateral tegmental field, nucleus tractus solitarii (NTS), nucleus commissuralis, nucleus reticularis rostroventrolateralis (RVL), and the ventral medullary surface (VMS). In the PBC, immunoreactive varicosities identified areas previously unexplored for cholinergic autonomic responsivity (superior, internal, dorsal, and central divisions of the lateral subnucleus, nucleus of Koelliker-Fuse and the medial subnucleus). In the NTS, previously undescribed ChAT-immunolabeled cells and processes were concentrated at intermediate and subpostremal levels and distributed viscerotopically in areas receiving primary cardiopulmonary afferents. In the nucleus RVL, cholinergic perikarya were in proximity to the VMS and medial to adrenergic cell bodies of the C1 area. Punctate varicosities of unknown origin and dendrites extending ventrally from the nucleus ambiguus overlapped the C1 area and immediate surround of RVL., In Conclusion: 1) Cholinergic perikarya and putative terminal fields, overlap structures that are rich in cholinoreceptors and express autonomic, neuroendocrine, or behavioral responsivity to central cholinergic stimulation (PHN, NTS, RVL). The role of ACh in most immunolabeled areas, however, has yet to be determined. Overall, these data support the concept that cholinergic agents act at multiple sites in the CNS and with topographic specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

In the ventrolateral medulla oblongata, clonidine binds not only to alpha 2-adrenergic receptors but also to a novel class of nonadrenergic sites that are specific for imidazoles. Since clonidine has direct actions on the kidney, we sought to determine whether imidazole binding sites could be detected in renal cell membranes. Adrenergic agents having an imidazole ring, like clonidine, completely displaced the specific binding of the high-affinity clonidine analog 3H-p-aminoclonidine (3H-PAC) to kidney membranes. Nonimidazole adrenergic agents inhibited 3H-PAC binding by only 75%, indicating that the remaining 25% of the sites were nonadrenergic. Cimetidine, an imidazole compound lacking adrenergic potency, showed a high affinity for approximately 25% of the sites. 3H-PAC binding to imidazole sites was high-affinity (KD = 11 +/- 3 nmol/L) and saturable (Bmax = 41 +/- 10 fmol/mg protein). Like clonidine, an endogenous clonidine-displacing substance (CDS) completely inhibited 3H-PAC binding to renal cortex membranes. Quantitative receptor autoradiography revealed that imidazole receptors exhibited a specific regional distribution within the kidney that was unique, and distinct from that of alpha 2-adrenergic receptors. We conclude that clonidine binds to specific imidazole sites in the renal cortex of the rat and that CDS may be the endogenous ligand at these sites. Thus, in addition to their role in central nervous system control of arterial pressure, imidazole receptors may be involved in the regulation of renal function.

We sought to establish whether the C1 area of the rostral ventrolateral reticular nucleus (RVL) of the medulla oblongata mediates: (1) the elevations in arterial pressure (AP), heart rate (HR) and regional cerebral blood flow (rCBF) elicited by electrical stimulation of the rostral cerebellar fastigial nucleus (FN), the fastigial pressor response (FPR); (2) the reductions in AP and HR elicited by chemical stimulation of intrinsic neurons of FN with excitatory amino acids, the fastigial depressor response (FDR). Studies were conducted on rats anesthetized (chloralose), paralyzed and artificially ventilated. The FN was stimulated electrically through microelectrodes and chemically by microinjection of D.L-homocysteic acid (100 nmol in 100 nl). rCBF was measured in homogenates of 11 brain regions by the 14C-iodoantipyrine technique. Bilateral electrolytic lesions restricted to the RVL abolished the elevations in AP, HR and rCBF elicited by electrical stimulation as well as the fall of AP and HR elicited by chemical stimulation of the FN. The disappearance of the responses was anatomically selective and could not be attributed to changes in resting AP, HR or rCBF, loss of reactivity of preganglionic sympathetic neurons, or variations in blood gases. Since the FN neither projects to nor receives afferents from the RVL the pathway to RVL is indirect. We conclude that: (1) the FPR results from excitation and the FDR inhibition of reticulospinal sympathoexcitatory axons of RVL; (2) the FPR is a consequence of excitation of axons arising from neurons in an as yet unidentified area of lower brainstem projecting to or through the FN and with collateral branches innervating RVL mono- or polysynaptically; (3) the FDR, in contrast, represents excitation of intrinsic FN neurons with a polysynaptic projection to RVL through unidentified regions of lower brainstem; (4) the RVL is a relay mediating the increase in rCBF associated with the FPR; and (5) the RVL plays a critical role in integrating actions on the systemic and cerebral circulation represented in cerebellum.

Heterogeneity among NPY (and PYY) receptors was first proposed on the basis of studies on sympathetic neuroeffector junctions, where NPY (and PYY) can exert three types of action: 1) a direct (e.g., vasoconstrictor) response; 2) a postjunctional potentiating effect on NE-evoked vasoconstriction; and 3) a prejunctional suppression of stimulated NE release; the two latter phenomena are probably reciprocal, since NE affect NPY mechanisms similarly. It was found that amidated C-terminal NPY (or PYY) fragments, e.g., NPY 13-36, could stimulate selectively prejunctional NPY/PYY receptors, which were termed Y2-receptors. Consequently, the postjunctional receptors which were activated poorly by NPY/PYY fragments, were termed Y1-receptors. Later work has indicated that the Y2-receptor may occur postjunctionally in selected sympathetic effector systems. The central nervous system appears to contain a mixture of Y1- and Y2-receptors as indicated by functional as well as binding studies. For instance, NPY and NPY 13-36 produced diametrically opposite effects on behavioral activity, indicating the action of the parent peptide on two distinct receptors. Cell lines, most importantly neuroblastomas, with exclusive populations of Y1- or Y2-receptors, have been characterized by binding and second messenger studies. In this work, selective agonists for the two receptor subtypes were used. Work of many investigators has formed the basis for subclassifying NPY/PYY effects being mediated by either Y1- or Y2-receptors. A preliminary subclassification based on effects of NPY, PYY, fragments and/or analogs is provided in Table 6. It is, however, to be expected that further receptor heterogeneity will be revealed in the future. It is argued that mast cells possess atypical NPY/PYY receptors. The histamine release associated with stimulation of the latter receptors may, at least in part, underlie the capacity of NPY as well as of short C-terminal fragments to reduce blood pressure. Fragments, such as NPY 22-36, appear to be relatively selective vasodepressor agents because of their weak vasopressor properties.(ABSTRACT TRUNCATED AT 400 WORDS)

We examined whether plasma epinephrine contributes to the increase in regional cerebral blood flow (rCBF) evoked by electrical stimulation of the dorsal medullary reticular formation (DMRF). Rats were anesthetized (alpha-chloralose, 30 mg/kg, s.c.), paralyzed and artificially ventilated. The DMRF was electrically stimulated through microelectrodes stereotaxically implanted. During stimulation, blood gases and arterial pressure were monitored and maintained within normal range. rCBF was determined in 11 dissected brain regions using the [14C]iodoantipyrine technique. Plasma epinephrine and norepinephrine were measured radioenzymatically in rats with intact adrenals or adrenalectomy, and with or without infusion of epinephrine. DMRF stimulation induced widespread increases in rCBF associated with a 50-fold increase in plasma epinephrine and a 20-fold increase in norepinephrine without changes in the electroencephalogram. In contrast, stimulation of the adjacent medial longitudinal fasciculus had no effect upon rCBF or plasma catecholamines. Acute bilateral adrenalectomy produced regionally selective reductions in the stimulation-coupled increases in rCBF throughout brain (P less than 0.05). Infusion of epinephrine in adrenalectomized rats to levels comparable to those observed in intact animals during DMRF stimulation did not by itself modify rCBF. However, when infused in conjunction with stimulation of the DMRF, but not medial longitudinal fasciculus, epinephrine fully restored the stimulus-related increases in rCBF in all brain regions to levels comparable to those observed in intact rats. We conclude that stimulation of the DMRF elevates rCBF through two mechanisms; by a neurally-mediated increase in local metabolism and thereby flow (adrenal independent secondary vasodilation) and by releasing epinephrine from adrenal medulla which secondarily acts to increase rCBF by an action on brain.

Clonidine, an alpha 2-adrenergic agonist, also binds to non-adrenergic imidazole receptors in brain and peripheral tissues. In adrenal medulla, however, clonidine appears to bind only to imidazole receptors. To assess whether the signal transduction mechanism of imidazole receptors differs from alpha 2-adrenergic receptors, we studied the actions of clonidine on the turnover of phosphoinositide and the production of cAMP and cGMP in slices of rat adrenal gland. Clonidine did not modify basal or carbachol mediated increases in phosphoinositide turnover or production of cAMP, however it increased the production of cGMP. The increase in cGMP was slow and unaffected by the addition of the phosphodiesterase inhibitor, IBMX. We conclude that the second messenger response triggered by clonidine in adrenal differs from that usually coupled to alpha 2-adrenergic receptors. Whether the effect is mediated by cell surface imidazole receptors remains to be established.

In brain, a major factor regulating local perfusion is local neuronal activity. However, we have recently discovered that, in rat, five days after selective neuronal destruction in the parietal cortex by local microinjections of the excitotoxin ibotenic acid, local cerebral blood flow, within the lesion, remains in the normal range. We studied whether proliferating non-neuronal cells and/or local changes in microvascular density participate to maintain local cerebral blood flow. Rats were anesthetized (halothane 1-3%), ibotenic acid (10 micrograms in 1 microliter) was locally microinjected in a restricted region of the parietal cortex, and animals were allowed to recover. Three, five, seven, 11, 30 days later local cerebral blood flow was measured autoradiographically under chloralose anesthesia (40 mg/kg, s.c.) by the [14C]iodoantipyrine technique. Cellular density or microvascular area were determined on sections stained with Thionine or processed for the endothelial marker alkaline phosphatase, respectively. Local neurons were destroyed by 24 h after microinjections of ibotenic acid. However, from three to 11 days after lesion local cerebral blood flow was unchanged (P greater than 0.05; n = 5), thereafter declining so that by 30 days blood flow was 48 +/- 6% of control (P less than 0.05; n = 5). Cellular density increased within the lesion by 17.5-fold at seven to 11 days (P less than 0.01) and declined to a 11.7-fold elevation above control at day 30 (P less than 0.01). New cells consisted of macrophages, endothelium and glial fibrillary acidic protein-positive astrocytes. The microvascular area increased 4.2-fold from three to 11 days (P less than 0.01). The patency of the presumably newly formed vessels was determined by the presence of intravascular red blood cells, which were revealed histochemically. The area occupied by red blood cells within cerebral microvessels, in contrast to microvascular area, did not increase until seven days after lesion, reaching a 3.2-fold increase at 11 days. Thus within the lesion, local cerebral blood flow remains constant during the phase in which cellular and microvascular density increases. The presumably newly formed vessels cannot contribute to maintain local cerebral blood flow since during this phase they are not patent; rather patency develops coincident with the decline in local cerebral blood flow. We conclude that non-neuronal cells, most likely activated macrophages, may be an important factor regulating local cerebral perfusion, after acute neuronal death.

This report investigates the contributions of the sympathetic nerves and adrenal medulla to resting mean arterial pressure (MAP) and to emotionally conditioned MAP and heart rate (HR) responses in unrestrained spontaneously hypertensive rats (SHR) and Wistar-Kyoto normotensive control rats (WKY). Resting MAP (in mm Hg), which was higher in SHR (WKY = 120 +/- 4; SHR = 163 +/- 4; p less than 0.01), did not differ in the two strains following chemosympathectomy (WKY = 105 +/- 2; SHR = 101 +/- 2; n.s.). Adrenal medullectomy did not affect resting MAP in WKY (125 +/- 6; n.s.) but lowered it in SHR (146 +/- 5; p less than 0.05), relative to controls (see above). The conditioned pressor response (in mm Hg) in controls consisted of two peaks (I, II) in both strains, but was exaggerated in SHR (I = WKY, 13 +/- 1; SHR, 25 +/- 2; p less than 0.01; II = WKY 10 +/- 2; SHR 20 +/- 2; p less than 0.01). Chemosympathectomy suppressed (relative to controls) the first peak, but not the second, in both strains (WKY: I = 4 +/- 1, p less than 0.01; II = 12 +/- 2, n.s.; SHR: I = 6 +/- 1, p less than 0.01; II = 15 +/- 2, n.s.). Adrenal medullectomy alone had little effect on the pressor response, but when combined with chemosympathectomy both peaks were largely eliminated (WKY: I = 2 +/- I; II = 5 +/- 1; SHR: I = 1 +/- 0; II = 2 +/- 0). These data indicate that: 1) hypertension in conscious, freely behaving SHR is largely sustained by the sympathetic vasomotor nerves but that the adrenal medulla contributes to the magnitude of the elevation; 2) the early component of the exaggerated pressor response during aversive stimulation is mediated by sympathetic vasomotor excitation; and 3) the later component of the exaggerated pressor response reflects coactivation of the sympathetic vasomotor nerves and the adrenal medulla.

The purpose of this study was to determine whether the reduced conditioned fear response in spontaneously hypertensive rats (SHRs) relative to Wistar-Kyoto controls (WKYs); (a) reflects a decrease in fear in SHRs or an increase in fear in WKYs, relative to other strains; (b) is secondary to strain differences in cardiovascular regulation; (c) represents a weaker conditioned response or a weaker memory trace; and (d) generalizes beyond tests of conditioned fear. SHRs, WKYs and Sprague-Dawley (SD) rats were subjected to classical fear conditioning (30 trials) involving the pairing of a tone conditioned emotional stimulus (CES: 800 Hz, 82 dB, 10 s) with an electric footshock unconditioned stimulus (US: 1.5 mA, 0.5 s). Cardiovascular responses elicited by the CES (without the US) were assessed through computer assisted techniques in chronically instrumented animals. Conditioned fear behavior was assessed as the proportion of time accounted for by crouching or freezing during a 300 s presentation of the CES without the US. Unconditioned fear reactivity was examined using the open field test. Conditioned fear reactivity (% freezing during 300 s CES) was reduced (P less than 0.01) in SHRs relative to both WKYs and SDs, which did not differ (SHR: 57% +/- 5; WKY 85% +/- 3; SD: 93% +/- 4). Young (7 week) and mature (14 week) animals within each strain differed in resting mean arterial pressure (MAP, in mm Hg) (WKY: young , 102 +/- 1; mature, 133 +/- 2; P less than 0.01; SHR: young, 124 +/- 3; mature, 153 +/- 5; P less than 0.01) but did not differ in conditioned fear reactivity (WKY: young, 91% +/- 3; mature, 93% +/- 3; SHR: young, 47% +/- 3; mature, 62% +/- 8.(ABSTRACT TRUNCATED AT 250 WORDS)

The possibility that L-glutamic acid (L-Glu) might be the neurotransmitter of baroreceptor afferents terminating in the nucleus tractus solitarius (NTS) and affecting activity of the autonomic nervous system was tested using a variety of techniques. Effects on blood pressure and heart rate of microinjections of L-Glu and antagonists into the NTS supported this contention. Use of blocking agents was confirmatory. Biochemical studies provided evidence that the agent (glutamic acid) is synthesized, stored and reaccumulated in these nerve endings. Furthermore, it was shown that L-Glu is released from the NTS in vivo. Degeneration of afferent terminals due to removal of the nodose ganglia reduced L-Glu levels in the NTS. After discussion of this and additional evidence that L-Glu is the transmitter and a consideration of reasons for eliminating other possibilities (substance P, etc.) it was concluded that L-glutamic acid is the neurotransmitter of baroreceptor afferents.

This study further analyzed the environmental and genetic mechanisms underlying the previously reported strain differences in tyrosine hydroxylase (TH) activity in the nigrostriatal and hypothalamic dopamine system of the BALB/cJ (B) and CBA/J (C) inbred mouse strains and related behavioral processes using parental and reciprocal F1 hybrid generations. Significant strain differences were found in both sexes in all the measured characters. Comparing males and females, sexual dimorphisms were found in TH activity of substantia nigra (SN), corpus striatum (CS) and hypothalamus (H), and in exploratory behavior (IE). Presence of sexual dimorphism was genotype dependent, with the exception of TH activity in H. Major components of strain differences, maternal effects and additive gene effects, were separated by biometrical genetic methods. The analysis indicated that significant maternal effects were present in TH activity of TH and CS with a trend towards this phenomenon in the SN. Additive gene effects were significant in all characters and various degrees of dominance were expressed in the hybrids in TH activity of SN and CS, as well as in behavioral traits, IE and spontaneous locomotion (SL). All the biochemical and behavioral parameters were expressed at lower levels in CBA/J than in BALB/cJ mice and reciprocal F1 hybrids took intermediate positions between the two parental strains for all phenotypes examined, with the exception of IE, where complete dominance was found in (CXB)F1 females. These results are consistent with the hypothesis that some of the genes affecting TH activity in brain dopamine systems contribute to the expression of dopamine mediated behaviors. Our analysis also indicates the possibility that the maternal effects on TH activity in CS and SN are the consequences of X-chromosome linked gene effects. We suggest that the influence of the X-chromosome linked gene(s) is dependent upon the action of gonadal steroids during the critical period of ontogenesis, and X-chromosome linked gene(s) play a major role in the genotype dependent expression of sexual dimorphism in TH activity.

We postulate that the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH), dopamine B-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) are coded for by similar gene coding sequence(s). This is based on the following observations: (1) proteolytic digestion of these enzymes produces similar peptides whose amino acid composition is nearly identical; (2) antibodies to each enzyme coprecipitate more than one of these enzymes from in vitro poly(A)mRNA translation products; (3) using hybrid selection analysis to positively identify the cDNA clones, we discovered that DBH cDNA clones cross-hybridize with PNMT mRNA, and PNMT cDNA cross-hybridize with DBH mRNA; (4) DNA hybridization analysis demonstrated that DBH and PNMT cDNA probes hybridized to several common restriction fragments of total cellular DNA. The evidence suggests that these enzymes are coded for by a single gene or linked genes coding for all catecholamine enzymes.

Newborn rats were daily injected with 0.2 mg hydrocortisone acetate for seven days. They were killed 1, 7 or 21 days after the last injection, together with untreated controls. Hydrocortisone caused a great increase in the number of the small, intensely fluorescent (SIF) cells and the appearance of similar small cells with intense immunohistochemical reactions for tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine (noradrenaline) N-methyltransferase (PNMT) in the superior cervical ganglion. At the same time, the adrenaline content and the PNMT activity of the ganglion greatly increased, while no significant changes were observed in the dopamine or noradrenaline content or TH or DBH activity. All these changes essentially disappeared after a recovery period of seven or 21 days. It is concluded that hydrocortisone caused a temporary increase in the number of SIF cells by causing a synthesis of TH, DBH and PNMT in previously existing small, non-fluorescent cells, which start to synthesize and store adrenaline, thus becoming intensely fluorescent SIF cells. These SIF cells are different from the normal SIF cells of the same ganglion, most of which appear at a later stage of postnatal development when response to hydrocortisone is lost, which contain TH but neither DBH nor PNMT, and which permanently remain in the ganglion.

The catecholaminergic and peptidergic neurons in the area postrema and adjacent portion of the medial nucleus tractus solitarii (mNTS) were characterized by the immunocytochemical localization of the catecholamine synthesizing enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) and two neuropeptides, substance P and (Leu5)-enkephalin. The catecholamine synthesizing enzymes TH and DBH, found jointly only in noradrenergic and adrenergic neurons, were localized in cells having a similar morphology and topographical distribution. These cells were located throughout the rostrocaudal and dorsoventral extent of the area postrema, as well as in neurons within the mNTS. The processes showing TH and DBH immunoreactivity appear to form reciprocal connections between the area postrema and mNTS. Phenylethanolamine-N-methyltransferase, the enzymatic marker found only in adrenergic neurons, was detected immunocytochemically in terminals distributed throughout the area postrema and in neuronal perikarya and varicosities within the adjacent mNTS. Like the catecholamine synthesizing enzymes TH and DBH, enkephalin-like immunoreactivity was localized to perikarya, proximal processes and varicose axon terminals within the area postrema and the adjacent mNTS. However, in contrast to the widespread distribution of the enzymes, the enkephalin-like immunoreactivity was localized predominantly along the dorsal and ventrolateral margins of the area postrema. The distribution of substance P immunoreactivity, which was detected only in varicose processes, paralleled the distribution of enkephalin-like immunoreactivity, being predominantly located along the dorsal and ventrolateral margins of the area postrema. Within the mNTS adjacent to the area postrema, substance P immunoreactivity was localized to neuronal perikarya, proximal processes and varicose axon terminals. Based upon the presence of appropriate biosynthetic enzyme markers and neuropeptide localization, these findings suggest that neurons within the area postrema contain noradrenalin and enkephalin and that the afferent axons contain substance P, adrenalin and, probably, noradrenalin.

Bilateral electrolytic lesions of the anterior hypothalamus in unrestrained rats resulted in the development, within 2 hours, of arterial hypertension, tachycardia, hyperthermia, and increased locomotor activity, often leading to pulmonary edema and death. Similar lesions in paralyzed, artificially ventilated rats produced comparable changes in arterial blood pressure and body temperature with a similar time course. The arterial hypertension was a consequence of an increase in total peripheral resistance to 15% of control with a reduction in cardiac output to 49% of control. Arterial hypertension, elevated peripheral resistance, and diminished cardiac output were reversed toward normal by alpha-receptor blockade with phentolamine (1 mg/kg, iv). Bilateral adrenalectomy, adrenal demedullation, or adrenal denervation performed prior to lesion placement prevented the development of arterial hypertension and pulmonary edema as well as the changes in peripheral resistance, cardiac output, and body temperature. We conclude that arterial hypertension following lesions of the anterior hypothalamus is due to a neurally mediated increase in peripheral resistance initiated by the release of adrenal medullary catecholamines and that pulmonary edema is due to myocardial failure secondary to the ensuing ventricular overload. Structures originating in or passing through the anterior hypothalamus may exert selective control over the adrenal medulla independent of vasomotor neurons.

The centrally active muscarinic agonist, oxotremorine, elicited an up to 2-fold dose-dependent (0.25-1.5 mg/kg) increase in the activity of tyrosine hydroxylase (TH) in the rat nucleus locus coeruleus (LC) and adrenal medulla. The response occurred in LC after 24 to 48 hours and in adrenal medulla by 4 to 8 hours, peaked in LC at 72 hours and adrenal medulla at 16 to 24 hours and persisted up to 2 weeks in both tissues. In brain the effect appeared confined to cell bodies of noradrenergic neurons. The activity of dopamine beta-hydroxylase increased in adrenal medulla (40%) but not in brain. Immunotitration with anti-TH serum demonstrated that the increase of TH activity in LC is due to increased catalytic activity (activation), whereas in adrenal medulla it is due to a transynaptically mediated accumulation of enzyme protein (induction). Physostigmine (1.0 mg/kg), pilocarpine (25-50 mg/kg) and nicotine (10 mg/kg) increased TH activity in LC and adrenal. We conclude that stimulation of central cholinergic receptors of the muscarinic type results in a delayed and protracted activaiton of TH but not of dopamine beta-hydroxylase in cell bodies of central noradrenergic neurons, and reflexly, to transynaptic induction of TH and dopamine beta-hydroxylase in the adrenal medulla.

Recent reports have identified discrepancies between the anatomical distribution of transmitters and their receptors, a phenomenon known as transmitter-receptor mismatch. However, quantitative determinations of transmitter activity and receptor density in individual brain regions have not been conducted in parallel. We therefore sought to determine quantitatively the relationship between muscarinic acetylcholine receptor density and the density of cholinergic innervation as reflected by activity of the biosynthetic enzyme for acetylcholine, choline acetyltransferase (ChAT). To assure sampling of equivalent regions using the two methods, an 'electronic micropunch' technique was developed to allow measurement of [3H]quinuclidinyl benzilate ([3H]QNB) binding within the corresponding cylinders of tissue obtained by the micropunch cannula. Nineteen regions of the rat medulla (1 mm diameter, 1 mm height) were studied. The micropunch region containing the gracile nucleus, the area postrema and the choroid plexus of the fourth ventricle contained the highest ChAT activity, but exhibited little [3H]QNB binding to muscarinic receptors. However, among the remaining 18 regions a strong correlation was obtained between uncorrected muscarinic receptor density and ChAT activity within each micropunched region (r = 0.89, n = 18). Correction for autoradiographic efficiency weakened the overall relationship between receptor density and ChAT activity (r = 0.58, n = 18). This was due to a relatively high density of receptors associated with fiber tract regions containing low ChAT activity. The presence of receptors within white matter is ordinarily obscured by high tritium quenching. This is consistent with the hypothesis that a portion of muscarinic receptors are located extrasynaptically and may be present within axons.(ABSTRACT TRUNCATED AT 250 WORDS)

Previous studies have demonstrated that, in rat, individual sympathetic neurons can express both adrenergic and cholinergic biosynthetic enzymes in culture. Moreover, the levels of these enzymes can be regulated by factors present in their environment. In the present study, we sought to determine whether cultures of chick sympathetic neurons express both adrenergic and cholinergic enzymes, whether both enzymes are expressed in the same neurons, and whether the levels of these enzymes can be influenced by environmental factors. In our system, we tested one such factor found in embryonic eye extract (EEE) which has been shown to specifically increase the activity of the cholinergic enzyme choline acetyltransferase (ChAT) in cultures of chick parasympathetic neurons Varon et al., Brain Res., 173 (1979) 29-45; Nishi and Berg. J. Neurosci., 1 (1981) 505-513). At various times in vitro, cultures were analyzed using biochemical, immunocytochemical and autoradiographic techniques. We found that only those cultures of sympathetic neurons supplemented with EEE developed detectable levels of ChAT enzyme activity at 2 days, which increased significantly by 14 days in vitro. Supplementation with EEE did not affect the level of tyrosine hydroxylase (TH) activity. Furthermore, irrespective of nutrient medium, all neurons in all cultures contained TH immunoreactivity and possessed a high-affinity amine uptake system as demonstrated by autoradiography. These studies suggest that neurons of chick sympathetic ganglia can be influenced by factors present in EEE to express a cholinergic enzyme and that this enzyme is coexpressed by cells also exhibiting an adrenergic phenotype.

Electrical stimulation of the nucleus parabrachialis (NPB) and surrounding areas of the dorsolateral pons in anesthetized immobilized cats elicits a rise of arterial pressure (AP) and tachycardia: the parabrachial pressor response (PBPR). The most excitable sites were concentrated within the intermediate one-third of the NPB in its medial and lateral subdivisions. The magnitude of pressor responses and their stimulus sensitivity were substantially greater in NPB than in adjacent areas of the dorsal pons including nucleus locus coeruleus and brachium conjunctivum, suggesting that cardiovascular responses heretofore attributed to locus coeruleus may have been due to excitation of the NPB. The PBPR persisted after chronic cerebellectomy, acute transection of the brain stem at the lower midbrain, or acute bilateral lesions of the nucleus tractus solitarii (NTS), the latter abolishing baroreceptor reflexes. Thus the PBPR cannot be attributed to antidromic or orthodromic stimulation or from NTS. Change in blood flow and regional vascular resistances during the PBPR were measured by electromagnetic flow meters placed on the thoracic aorta, superior mesenteric, renal and femoral arteries. When elicited with stimuli 5 times threshold, the PBPR was associated with an 80% increase in AP, 14+ increase in heart rate, 25% increase in cardiac output, and a 42% increase in total peripheral resistance. There was a differentiated vasoconstriction in the order of superior mesenteric greater than renal greater than femoral arteries. The baroreflex elicited by electrical stimulation of the carotid sinus nerve was reduced during stimulation of the NPB. The tachycardia was abolished by bilateral vagotomy, combined with beta-adrenergic blockade. Such treatment attenuated but did not abolish the hypertension which was only eliminated by subsequent alpha-adrenergic blockade. Thus the hypertension caused by stimulation of NPB is a result both of an increase of total peripheral resistance and of cardiac output. The cardiovascular pattern of the PBPR differ from other responses elicited from the dorsal pons, including the defense response, and the response to cerebral ischemia. We conclude that a powerful cardiovascular response pattern is organized within intrinsic neurons of the NPB. This nucleus may play an important role in organization of cardiovascular control by brain.

The activity of tyrosine hydroxylase [TyrHase; tyrosine-3-monooxygenase; L-tyrosine, tetrahydropteridine: oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] is 20% less in whole midbrain of CBA/J mice than BALB/cJ mice and is paralleled by a comparable difference in the number of dopaminergic neurons in which the enzyme can be detected immunocytochemically. The strain-dependent difference in numbers of TyrHase-containing neurons and of TyrHase activity is not homogeneous in the midbrain but is restricted (along the rostral-caudal axis) to the medial one-third, where almost 2-fold variations are found. The volume of the striatum, a major projection field of midbrain dopamine neurons, is 20% smaller in CBA/J than in BALB/cJ mice; the difference is regional and is concentrated in the caudal half. Because the packing density of intrinsic neurons of the striatum is similar in both strains, CBA/J mice contain 20% fewer neurons than do BALB/cJ mice. The activities of TryHase and of choline acetyltransferase (ChoAcTase; acetyl-CoA:choline-O-acetyltransferase, EC 2.3.1.6) in the whole striatum of CBA/J mice are less than in BALB/cJ. The strain-dependent differences in midbrain TyrHase activity are due to variations in the number of dopamine neurons and directly correlate with differences in the number of striatal cholinergic neurons. There is genetic control of the number of neurons of a neurochemically specific class in the mammalian brain.

Polyclonal antisera raised against para-aminoclonidine coupled to haemocyanin exhibit high affinity for para-aminoclonidine, clonidine and chloroethylclonidine (IC50 less than 100 nmol/l). Anti-para-aminoclonidine antibodies also cross-react with naphazoline, oxymetazoline and tolazoline at moderate concentrations (IC50, 300-500 mumol/l); the phenyl-imidazoles detomidine, medetomidine and MPV830 are weakly cross-reactive (IC50 greater than 0.2 mmol/l). All of these compounds bind with high affinity to both imidazole and alpha 2-adrenergic receptors. Compounds which are imidazole- or alpha 2-specific do not cross-react with anti-para-aminoclonidine antibodies (IC50 greater than 1 mmol/l). Anti-para-aminoclonidine also recognizes an endogenous clonidine-displacing substance in the brain. Thus, (a) binding to anti-para-aminoclonidine antibodies defines a subset of phenyl-imidazol(in)e ligands which bind to both imidazole and alpha 2-adrenergic receptors, suggesting that anti-para-aminoclonidine recognition sites resemble a hybrid of the two receptor types; (b) antibodies to imidazole- or alpha 2-specific agents may be useful as models for differentiating between these types; (c) since clonidine-displacing substance is recognized by anti-para-aminoclonidine antibodies, it may have phenyl and imidazole rings as parts of its chemical structure.

Using biochemical parameters the present study sought to assess the normal developmental pattern of the dopaminergic innervation of the olfactory tubercle (OT) and how it is affected by olfactory bulbectomy. In rats, the adult pattern of cellular organization is achieved in the OT gradually over the first 7 days after birth. On the other hand, tyrosine hydroxylase (TH) and [3H]dopamine ([3H]DA) uptake, while present at low levels, start to increase rapidly only after the first 7 days reaching adult levels by 40 and 20 days after birth, respectively. TH in dopamine (DA) cell bodies of A10 was already high, 40% of adult value, at birth, reached 150% by day 14 and decreased back to adult values by day 21 after birth. In 10-day-old rats, bulbectomy resulted, 30 days later, in an increase to 123% of control in TH activity and 137% in [3H]DA uptake within the OT. Comparable changes were found following bulbectomy in adults. However, bulbectomy in 1-day-old rats did not produce any significant changes 40 days later. The findings suggest that during postnatal growth TH activity is increased in DA cell bodies, preceding the changes in DA terminals of the OT, resembling the changes occurring during collateral sprouting in adults. In addition, changes indicative of collateral sprouting do not occur in response to deafferentation of the OT in 1-day-olds but do in 10-day-olds or older animals, a phenomenon probably related to a critical development period of the OT.

Experiments were performed to test the hypothesis that A1 noradrenergic neurons, in the caudal ventrolateral medulla, have an inhibitory cardiovascular function. The lateral portion of the caudal medulla was systematically explored, using focal electrical stimulation, in anesthetized, paralyzed rabbits and arterial pressure and heart rate responses were recorded. Since electrical stimulation activates fibers of passage as well as neuronal cell bodies, we also determined cardiovascular responses to microinjections of L-glutamate, a neuroexcitatory amino acid with minimum effects on fibers of passage. Histological studies of stimulation sites were combined with catecholamine fluorescence histochemical studies to localize the A1 cells. A decrease in arterial pressure and heart rate, restricted to the region containing A1 cells, was observed with low frequency stimulation and with microinjections of L-glutamate. In contrast, when GABA, an inhibitory amino acid, was microinjected into the A1 region, we observed an increase in arterial pressure and heart rate. L-Glutamate and GABA responses were dose-related. The fall in pressure was independent of the fall in heart rate. Results support our hypothesis, providing evidence that neurons in the A1 area tonically inhibit sympathetic vasomotor tone.

The purpose of this study was to identify thalamic areas receiving convergent sensory inputs from acoustic and spinal projection systems in the rat. The topographic distribution of afferents to the thalamus from the inferior colliculus and spinal cord was examined by using WGA-HRP as an anterograde axonal tracer. Following injections in the inferior colliculus, terminal labeling was present in ventral, medial, and dorsal divisions of the medial genicuate body (MGB) and in adjacent areas of the posterior thalamus, including the posterior limitans nucleus, the posterior intralaminar nucleus, the marginal zone, the peripeduncular region, the lateral or parvicellular part of the subparafascicular nucleus, and a region intercalated between the posterior limitans nucleus and the suprageniculate nucleus. In the caudal thalamus spinal projections remained in the reticular formation medial to the collicular terminal field. At intermediate levels of the MG, however, the spinal projection began to overlap the collicular field, terminating in the medial division of the MG and in the posterior intralaminar nucleus, the marginal zone, the lateral subparafascicular nucleus, and the area between the suprageniculate and posterior limitans nuclei. More rostrally, the convergent field expanded to include aspects of the dorsal MG division. The extent to which afferent projections to the thalamus from the inferior colliculus and spinal cord converge is thus graded in the caudorostral plane, with the greatest overlap occurring at the level of the rostral third of the MGB. These observations identify potential areas of acoustic and somesthetic integration and may account for observations of neuronal plasticity in the thalamus in response to the pairing of acoustic and somesthetic inputs.

Substance P (SP) and catecholamines, particularly adrenaline, have been implicated in cardiovascular responses mediated by neurons in the rostral ventrolateral medulla (RVL). Immunoperoxidase labeling of an antiserum against SP and/or immunoautoradiographic localization of catecholamine (tyrosine hydroxylase-TH)- or adrenaline (phenylethanolamine N-methyltransferase-PNMT)-synthesizing enzymes were examined histologically to determine the cellular basis for a functional interaction involving either synaptic or intracellular relations between these putative transmitters in the adult rat RVL. Peroxidase labeling for SP was localized in perikarya, dendrites, and axon terminals. Most of these perikarya were located medial and ventral to those labeled with TH or PNMT within the same section. However, as others have previously demonstrated by light microscopy, colocalization of SP-like immunoreactivity (SPLI) and PNMT was seen in a few perikarya of colchicine treated animals. Both single- and dual-labeled perikarya contained abundant dense core vesicles. The terminals with SPLI were 0.4-1.4 micron in diameter and contained a few mitochondria, a large population of small, clear vesicles, and from three to 11 large dense core vesicles. In some cases the terminals were seen in continuity with more proximal processes of neurons in the RVL. These terminals formed synapses with a few perikarya and many dendrites, some of which also contained SPLI. In the material dually labeled for TH and SP, terminals with SPLI (n = 32) formed synaptic junctions primarily with TH-labeled dendrites (69%); the remainder were with TH-labeled perikarya (6%) or with unlabeled dendrites (25%). The axosomatic junctions were exclusively symmetric, whereas the majority of axodendritic junctions were primarily asymmetric on small dendrites (0.8-1.0 micron in diameter) or dendritic spines. In sections dually labeled for PNMT and SP, the terminals containing SPLI (n = 37) formed synaptic associations with PNMT-labeled perikarya (11%), PNMT-immunoreactive dendrites (59%), or with perikarya and dendrites lacking PNMT immunoreactivity (30%). The axosomatic junctions were all symmetric and most often associated with the spinous portion of the soma. The axodendritic junctions were primarily asymmetric and were found both on the spinous portion of the PNMT-labeled dendrites. In addition, both TH- and PNMT-labeled somata and dendrites received symmetric and asymmetric contacts from terminals lacking SPLI.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrical stimulation of the fastigial nucleus in anesthetized, paralyzed, and artificially ventilated rats for 10 seconds (50 Hz) induced a stimulus-locked elevation of arterial pressure (the fastigial pressor response) and increased plasma vasopressin. Cervical spinal cord transection abolished the stimulus-locked fastigial pressor response and augmented the vasopressin response to a 10-fold increase (19 +/- 1 to 188 +/- 58 pg/ml, P less than 0.05; n = 8). Grading the pressor elevations occurring during the fastigial nucleus stimulus changed the amounts of vasopressin released in the same animal: acute adrenalectomy and chemosympathectomy by guanethidine reduced the magnitude of the fastigial pressor response and facilitated the vasopressin release to fastigial nucleus stimulation (intact: 52 +/- 11 pg/ml; after adrenalectomy and chemosympathectomy, 254 +/- 73 pg/ml, P less than 0.05, n = 6). Subsequent intravenous administration of a bolus of phenylephrine to increase mean arterial pressure during fastigial nucleus stimulus, as in intact situation, reduced the vasopressin release (47 +/- 9 pg/ml). After sinoaortic denervation plus vagotomy, the fastigial pressor response was preserved; however, vasopressin still increased 11-fold (from 11 +/- 1 to 126 +/- 23 pg/ml, P less than 0.01, n = 8). Vagotomy alone did not affect the vasopressin resting level nor the 4-fold increase in response to fastigial nucleus stimulation. Therefore, stimulus-locked elevations of arterial pressure oppose, by reflex mechanisms mediated through baroreceptors, but do not prevent the release of vasopressin elicited by stimulation of the fastigial nucleus.