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Clozapine is an antipsychotic medication with superior efficacy in treatment refractory schizophrenia. The molecular basis of clozapine's therapeutic profile is not well understood. We studied behavioral effects of clozapine in Caenorhabditis elegans to identify novel pathways that modulate clozapine's biological effects. Clozapine stimulated egg laying in C. elegans in a dose-dependent manner. This effect was clozapine-specific, as it was not observed with exposure to a typical antipsychotic, haloperidol or an atypical antipsychotic, olanzapine. A candidate gene screen of biogenic amine neurotransmitter systems identified signaling pathways that mediate this clozapine-specific effect on egg laying. Specifically, we found that clozapine-induced increase in egg laying requires tyramine biosynthesis. To test the implications of this finding across species, we explored whether trace amine systems modulate clozapine's behavioral effects in mammals by studying trace amine-associated receptor 1 (TAAR1) knockout mice. Clozapine increased prepulse inhibition (PPI) in wild-type mice. This increase in PPI was abrogated in TAAR1 knockout mice, implicating TAAR1 in clozapine-induced PPI enhancement. In transfected mammalian cell lines, we found no TAAR activation by antipsychotics, suggesting that modulation of trace amine signaling in mice does not occur directly at the receptor itself. In summary, we report a heretofore-unknown role for trace amine systems in clozapine-mediated effects across two species: C. elegans and mice., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Prion protein (PrP) is a glycoprotein expressed on the surface of neurons and glial cells. Its pathological isoform (PrP(res)) is protease resistant, and involved in the pathogenesis of a number of transmissible encephalopathies (TSEs). One common feature of neurodegenerative diseases, including TSEs, is oxidative stress, which may be responsible not only for the dysfunction or death of neuronal cells, but also cognitive deficits. Clioquinol (5-chloro-7-iodo-8-quinolinol) chelates zinc and copper, which are involved in the deposition of amyloid plaques and acts as an antioxidant; increased lipid peroxidation has also been demonstrated in the early phases of PrP propagation. The aim of this study was to investigate the effects of clioquinol on the changes in motor and cognitive behaviours induced by scrapie infection, as well as its effects on oxidative stress and the neurotransmitters known to be involved in motor and cognitive functions. The results show that clioquinol counteracts the massive memory deficit induced by scrapie infection. This effect is not paralleled by neurochemical changes because the levels of all of the biogenic amines and their metabolites were reduced despite clioquinol treatment. The main biochemical change induced by clioquinol was a marked reduction in lipid peroxidation at all time points. The antioxidant effect of clioquinol can reduce functional impairment and thus improve memory, but clioquinol does not reduce PrP deposition or synapse loss, as indicated by the unchanged Western blot, histopathological and histochemical findings.

The relationship between changes in regional brain bioamine levels and the expression of intraspecies aggressive behavior was evaluated in two murine models. In one study, normal male mice were maintained either in aggregate (i.e., normal, intraspecies social behavioral controls) or isolated (i.e., developed, non-social intraspecies aggressive 'fighter' behavior) housing environments, and the accompanying changes in both olfactory tubercle (OT) and hypothalamic (HYPOTH), norepinephrine (NE), dopamine (DA) and serotonin (5-HT) concentration indices quantitated by high-performance liquid chromatography (HPLC) for analysis of behavior-related alterations in localized bioamine deposition loci. Intact mice which had been housed in isolation cages and which exhibited aggressive, intraspecies reflexive-biting ('fighter') behavior when introduced to a novel (stimulus) animal, exhibited significant (P<0.05) elevations in NE levels, and depressed DA concentrations, in the OT regions relative to aggregated controls, indicating an intrinsic social influence on the maintenance of basal adrenergic indices at this neural locus. No changes in 5-HT levels were indicated between control and aggressive, isolated 'fighter' groups in either OT or HYPOTH loci. In addition, the NE and DA levels in the HYPOTH samples of both control and aggressive groups were found to be comparable. In the second study, utilizing an alternate type of aggression-induced murine model, changes in bioamine parameters were determined from samples obtained from aggregated, olfactory-bulbectomized (Obx) mice which are recognized to exhibit an overt, intraspecies, reflexive-biting behavior as compared to sham-operated (control) mice housed under identical conditions. In these studies, Obx-mice exhibited a significant increase in 5-HT levels in the OT relative to sham-operated controls, but similar NE and DA concentrations. In addition, all hypothalamic bioamine indices were found to be comparable between control and Obx groups. These data, collected for both isolation-developed, and experimentally-induced (i.e., OBX), intraspecies aggressive models, indicate that the distinctive types of aggressive behaviors displayed by these two murine models are accompanied by specific alterations in regional bioamine levels within the OT of these groups, relative to controls. These data suggest that the specific type of overt aggressive behavior demonstrated by these models may be causally related to the identified changes in bioamine concentrations in the forebrain regions of the CNS, in loci recognized to participate in environmental recognition and social processing activities.

Biogenic amines in well defined subtypes of human temporal lobe epilepsy (TLE) have not been well characterized. Specimens from five patients with neocortical TLE (NTLE) and nine with mesial TLE (MTLE) were immediately placed in Ringer's lactate; stearate indicator microelectrodes were placed in temporal gray matter, Ag/AgCl reference microelectrodes and auxiliary microelectrodes were placed 3-7 mm contralaterally to the indicator microelectrode. Dopamine (DA), ascorbic acid (AA), norepinephrine (NE) and serotonin (5-HT) were identified by their characteristic oxidative potentials in vitro. Four of five patients with NTLE had NE depletion in temporal neocortex while eight of nine patients with MTLE had high concentrations of NE (chi-square P<0.01). Significant concentrations of DA were present in the temporal lobes of three of five NTLE patients but in only one of the nine MTLE patients (chi-square P<0.05). 5-HT was present in the neocortex of both NTLE and MTLE patients in similar concentrations. AA was found in the neocortex of one NTLE patient. These data support an association between NE depletion and NTLE. The relative NE deficiency along with the consistent presence of DA in NTLE patients suggest an impairment in the catecholamine pathway. The presence of AA, a co-factor in NE synthesis, in the neocortex of one NTLE patient may also be related since AA is a cofactor in NE synthesis.

Systemic administration of lipopolysaccharide (LPS) induces sickness behaviors, as well as alterations of hypothalamic-pituitary-adrenal functioning commonly associated with stressors. In the present investigation, it was demonstrated that systemic LPS treatment induced a sickness-like behavioral profile (reduced active behaviors, soporific effects, piloerection, ptosis), which appeared to be dependent upon the novelty of the environmental context in which animals were tested. As well, LPS induced anxiogenic-like responses, including decreased time spent in the illuminated portion of a light-dark box, reduced open-arm entries in a plus-maze test, and decreased contact with a novel stimulus object in an open-field situation. The behavioral changes were accompanied by increased plasma ACTH and corticosterone levels. As well, LPS induced increased turnover of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in the paraventricular nucleus (PVN), median eminence plus arcuate nucleus, hippocampus, as well as NE turnover within the locus coeruleus and DA turnover within the nucleus accumbens. Although these neurochemical variations were reminiscent of those elicited by stressors, LPS was not particularly effective in modifying DA activity within the prefrontal cortex or NE within the amygdala, variations readily induced by stressors. Whether the LPS-induced anxiogenic-like responses were secondary to the illness engendered by the endotoxin remains to be determined. Nevertheless, it ought to be considered that bacterial endotoxin challenge, and the ensuing cytokine changes, may contribute to emotionality and perhaps even anxiety-related behavioral disturbances., (Copyright 1999 Elsevier Science B.V.)

Interleukin-6 (IL-6) is one of several cytokines that can stimulate the hypothalamo-pituitary-adrenocortical (HPA) axis. Because IL-6 is produced in response to the administration of endotoxin (LPS) and interleukin-1 (IL-1), it is possible that IL-6 contributes to the neuroendocrine and neurochemical changes induced by them. In this study, intraperitoneal (i.p.) injection of LPS elevated plasma concentrations of IL-6 while activating the HPA axis in a dose-dependent manner. Both responses reached a peak at around 2-3 h. Mouse IL-1beta administration (100 ng, i.p.) induced large increases in plasma corticosterone and a substantial, but short-lived increase in plasma IL-6 with a peak at 2 h. Pretreatment of mice intraperitoneally with a monoclonal antibody to mouse IL-6 significantly attenuated the plasma ACTH and corticosterone responses to LPS at 3 h, but not at 1 h. Anti-IL-6 treatment also attenuated the LPS-induced increases of tryptophan and the serotonin catabolite, 5-hydroxyindoleacetic acid (5-HIAA), but not that of the norepinephrine catabolite, 3-methoxy,4-hydroxyphenylethyleneglycol (MHPG). Pretreatment of mice with anti-IL-6 significantly attenuated the IL-1-induced increases of plasma ACTH and corticosterone at 2 h, but not at 4 h. The IL-1-induced increases of MHPG, tryptophan and 5-HIAA in hypothalamus and brain stem were not significantly altered. These results suggest that IL-6 contributes to the later phases of the LPS- and IL-1-induced stimulations of the HPA axis and to the indoleaminergic responses to LPS, but not to IL-1., (Copyright 1999 Elsevier Science B.V.)

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to induce parkinsonism in man and non-human primates. Hypotheses concerning the mechanism of action of MPTP have been related to the pathogenesis of nigral cell death in Parkinson's disease. For instance, alterations of calcium influxes have been reported to be implicated in both MPTP-induced parkinsonism and Parkinson's disease. Recently, we reported that nimodipine, a blocker of L-type calcium channels, prevents dopaminergic MPTP-induced neurotoxicity in C57B1/6 black mice. The present study extended these rodent findings to the non-human primate model of Parkinson's disease and assessed the effects of nimodipine, continuously applied by pellet for 18 days, on behavioural, biochemical and histological parameters, following systemic application of MPTP in common marmosets (Callithrix jacchus). The experimental design involved five groups of common marmosets and a total of 24 animals. Monkeys assigned to group I (n = 4) received subcutaneously implanted vehicle pellets 7 days prior to subcutaneous saline injections (control). Monkeys of group II (n = 4) were treated with nimodipine pellets (80 mg) and saline injections. Marmosets in group III (n = 8) were treated with vehicle pellets and received 4 times MPTP (MPTP-HCl, 2 mg/kg body weight subcutaneously, separated by an interval of 24 h for a total of 4 days). Monkeys in group IV (n = 4) and V (n = 4) were treated as group-III animals except for the implantation of nimodipine pellets (80 mg and 120 mg, respectively) 7 days prior to toxin exposure. In common marmosets MPTP induced severe parkinsonian symptoms, a pronounced dopamine depletion in the caudate-putamen (more than 99% of control) and a loss of tyrosine hydroxylase immunoreactive cells in the substantia nigra (50% percent of control) 7 days after MPTP-administration. Pretreatment with nimodipine (120 mg pellets) did neither attenuate the behavioural impairments in MPTP-treated animals nor antagonize the striatal neurotoxin-induced dopamine depletion, but almost completely prevented (in a dose-dependent manner) the MPTP-induced decrease of nigral tyrosine hydroxylase immunoreactive cells. These data suggest that application of nimodipine, during the observation period of 7 days, protects against MPTP-induced neurotoxicity in common marmosets at the cellular nigral level, but not at the synaptic striatal level, implicating differential mechanisms of actions of MPTP-induced neurotoxicity at the nigral versus the striatal level.

Dopamine-derived 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol, Sal) and related compounds were examined for their selective neurotoxicity to dopamine neurons by injection into the rat striatum. Among salsolinol analogs examined, only N-methyl-(R)- salsolinol (NM(R)Sal) induced behavioral changes very similar to those in Parkinson's disease: hypokinesia, stiff tail, limb twitching at rest and postural abnormality. Biochemical analysis showed that after NM(R)Sal injection, NM(R)Sal itself and its oxidation product, 1-2-dimethyl-6,7-dihydroxyisoquinolinium ion (DMDHIQ+) accumulated in the striatum, and also in the substantia nigra definite amount of DMDHIQ+ was detected. Dopamine and noradrenaline were reduced in the striatum and more markedly in the substantia nigra, whereas serotonin and its metabolite were not affected. Morphological analysis revealed selective reduction of tyrosine hydroxylase (TH)-containing neurons in the substantia nigra after continuous NM(R)Sal administration in the striatum. These results demonstrate the selective cytotoxicity of NM(R)Sal to the dopamine neurons in the substantia nigra, and the possible involvement of this 6,7-dihydroxy-isoquinoline in the pathogenesis of Parkinson's disease is discussed.

We examined effects of a high dose of methamphetamine (MA) (4.02 mg free base/kg, s.c., at 2-h intervals, 4 injections) on extracellular concentrations of monoamines such as dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) and those of glutamate and other several amino acids in rat striatum (ST) and nucleus accumbens (NA) using in vivo microdialysis. Five days after the microdialysis, tissue concentrations of monoamines were measured. The toxic dose of MA markedly increased extracellular concentrations of DA, and decreased those of DOPAC, HVA and 5-HIAA in both ST and NA. Magnitude of the increase in DA release was not different between ST and NA. Extracellular concentrations of glutamate showed a gradual increase in ST, but not in NA, while other amino acids showed no changes in both ST and NA. Tissue concentrations of serotonin (5-HT) and 5-HIAA were decreased to 43-58% of control values in both ST and NA, whereas those of DA, DOPAC and HVA showed 43-54% decrease in ST but no changes in NA. These data suggest that the marked increase of DA release is not directly related to the MA-induced dopaminergic neurotoxicity. The increase in glutamate release found only in ST may be related to the dopaminergic damage in ST. It may be that enhanced release in DA and glutamate act synergistically to cause the dopaminergic neurotoxicity in ST. However, enhancement in glutamate release did not appear to be essential for the MA-induced serotonergic neurotoxicity.

The effects of the peptide fasciculin (FAS), a potent inhibitor of acetylcholinesterase (AChE) have been examined, following unilateral microinfusion, on tissue levels of monoamines in the rat substantia nigra and concomitant circling behaviour. Although FAS inhibited 87% of total AChE, the levels of dopamine and its metabolites remained unchanged. Furthermore, the treatment induced modest contraversive rotation which was markedly enhanced in the presence of a systemic challenge with apomorphine. This behavioural effect of FAS was partially reversed by systemically administered atropine. Any possible interaction of FAS with nigral dopamine systems was further investigated by testing the peptide in animals that five days earlier had undergone a 6-hydroxydopamine (6-OHDA) lesion of the SN such that dopamine and AChE were significantly but not completely reduced. In a majority of these animals, FAS treatment caused a reversal of the lesion induced ipsiversive rotation, ie restored contraversive rotation. It is concluded that in the SN, FAS can have biochemical and behavioural actions independent of local dopamine systems and linked to cholinergic transmission. In addition, treatment with FAS in the substantia nigra also reveals the possible existence of at least two distinct pools of AChE with, respectively, non-cholinergic and cholinergic actions.

Turnover of noradrenaline (NA), dopamine (DA), serotonin (5-hydroxytryptamine; 5-HT) and their metabolites has been measured after a 15-day vitamin E-deficient diet in adult hippocampus. Moreover, we have measured in vitro receptor binding of [3H]5-HT in hippocampal membranes from control and vitamin E-deficient rats. Turnover rates of 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxy-3-indolacetic acid (5-HIAA) have been assayed from the disappearance rates after blocking by pargyline inhibition of monoamine oxidase (MAO). DA, NA, 5-HT, normetanephrine (NMN) and 3-methoxytyramine (3-MT) turnover rates have been measured as accumulation rates of DA, NA, 5-HT, NMN and 3-MT after pargyline inhibition of MAO. An increase was found in the turnover rate of DA between control and experimental animals. In contrast, no changes were found in the turnover rate of 3-MT and DOPAC. No change was found in the turnover rate of NA although there was an increase of the turnover rate of NMN in vitamin E-deficient diets. No changes was found in the turnover rate of 5-HT although there was a decrease of 5-HIAA turnover rate in the animals fed on a low vitamin-E diet. With respect to the 5-HT1 receptors, no changes were found in the affinity (kd) but the receptor number (Bmax) was increased in vitamin E-deficient rats.

Previous experiments from our laboratory have shown a wide variety of time-dependent lateralized changes in behavior and nigrostriatal function following unilateral manipulation of the mystacial vibrissae of rats. The present experiment investigated the effects of unilateral radiofrequency lesion of the cortical vibrissae representation (the barrel fields) in light of these results. We measured lateralized changes in behavior as well as tissue monoamines in neostriatum and substantia nigra, between 1 and 16 days post-lesion. Short-term asymmetries in exploratory behavior (thigmotactic scanning) and neostriatal serotonin metabolism that lasted up to day 6 were seen. In substantia nigra, time-related asymmetries in dopamine concentrations were found with higher ipsilateral values on day 3 and higher contralateral values on day 6. After day 6, the animals had recovered from these acute effects and thereafter, neostriatal dopamine metabolism became asymmetrical. Also during this time, they showed a directional bias in spontaneous and apomorphine-induced turning. Finally, neostriatal serotonin was bilaterally elevated on day 16. These results parallel some of the effects previously seen following unilateral removal of the vibrissae, indicating that the barrel cortex is a critical link in the functional interaction between the vibrissae and basal ganglia.

Tissue concentrations of noradrenaline (NA), serotonin (5-HT), dopamine (DA) and selected metabolites were measured in the spinal cord, cerebellum, cerebral cortex and caudate-putamen of developing mice following intraventricular inoculation with murine cytomegalovirus (MCMV) on postnatal day 10. MCMV-infected animals exhibited transient signs of neurological impairment, including apparent hypertonicity of hindlimb extensors and abnormal gait, beginning on days 14-16 and continuing for 3-5 days. At the onset of neurological impairment, tissue concentrations of NA were significantly reduced in the spinal cord (20%), cerebellum (32%) and cerebral cortex (40%) of infected animals. Levels of 5-HT were significantly increased in the caudate-putamen (50%), while 5-hydroxyindoleacetic acid (5-HIAA) was increased in both the spinal cord (94%) and caudate-putamen (65%). The ratio of 5-HIAA/5-HT, which is frequently used as an estimate of turnover of 5-HT, was significantly increased in the spinal cord (90%) at the onset of neurological impairment. In the caudate-putamen of MCMV-infected animals, there were significant increases in the tissue levels of DA (37%), homovanillic acid (HVA, 41%) and 3,4-dihydroxyphenylacetic acid (DOPAC, 34%). All neurochemical parameters were normal in the MCMV-infected animals by postnatal day 70, approximately 50 days after the resolution of neurological signs. These results indicate transient alterations in monoamine metabolism in the developing nervous system during the pathogenesis of cytomegalovirus-induced movement and postural disorders.

We studied 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in 5 strains of rats by assessing mortality and brain monoamine changes after MPTP injections into the internal carotid artery. We then attempted to correlate the differences among rat strains in their susceptibility to MPTP neurotoxicity in vivo with MPTP oxidation by monoamine oxidase (MAO) of the cerebral cortex, striatum, and brain microvessels in vitro. Despite the fact that the carotid route delivers much higher amounts of MPTP to the ipsilateral cerebrum than can be achieved by systemic injections, no significant dopamine depletion occurred in ipsilateral striata of Sprague-Dawley rats (the most resistant strain), but significant reductions of about 40% in striatal dopamine were evident in the more sensitive strains. Decreased striatal dopamine levels in these latter rat strains were associated with increased dopamine turnover. Higher doses of MPTP resulted in acute death. MPTP-induced mortality was not affected, but striatal dopamine depletion was prevented, by MAO inhibition. Differences among rat strains in their susceptibility to MPTP neurotoxicity correlated best with MAO activity in their isolated brain microvessels, but not with MAO activity in their striata or cerebral cortices. These results are consistent with the hypothesis that the rats' resistance to MPTP neurotoxicity is to some extent a property of their unique brain endothelium which has high MAO activity.

Effects of controllable and uncontrollable footshock on monoaminergic activity in the frontal cortex and plasma corticosterone levels were studied in male and female rats. Subjects were exposed to a shuttle-box procedure for a period of either 30 min (60 shocks) or 90 min (180 shocks). A shuttle response ended shock presentation for escape subjects, whereas their yoked, same-sex, counterparts were unable to escape from shock presentation. A third group was exposed to the experimental environment, but did not receive any shocks. Concentrations of noradrenaline, serotonin and dopamine and their major metabolites were measured in the frontal cortex by high performance liquid chromatography with electrochemical detection. Plasma corticosterone was measured by radioimmunoassay. Results of this experiment show that: (1) exposure to the experimental environment without shock already increased the activity of all 3 transmitter systems. In particular, serotonin was very responsive to mere confinement to the shuttle-box. Changes induced by exposure to the experimental environment were similar for males and females. (2) Presentation of footshocks further increased transmitter activity. The activation of noradrenaline and dopamine was larger after uncontrollable shock than after controllable shock. Moreover, uncontrollable shock resulted in higher serotonin levels than controllable shock. (3) Sex-dependent effects of controllability were found for noradrenaline and dopamine, but not for serotonin. Differences in catecholaminergic activity between controllable and uncontrollable shock were larger in females than in males. (4) In both males and females, corticosterone levels in plasma were increased by exposure to the experimental environment. A further elevation was found in response to footshock presentation, which was independent of the controllability of shock.

Push-pull cannulae were implanted into the arcuate nucleus of pregnant or ovariectomized (OVX) rats, and the perfusate samples were analyzed for biogenic amines and their metabolites. Injection of pargyline, a monoamine oxidase inhibitor, resulted in a decrease in 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) levels in the samples, and detectable amounts of dopamine (DA) and serotonin (5-HT), which were usually not measurable prior to injection. Administration of 5-hydroxytryptophan resulted in a sharp increase in 5-HIAA and 5-HT levels in the perfusates, and no change in DOPAC levels. Push-pull perfusion was done between midnight and 06.00 h on day 8 and 16 of pregnancy. In those rats which showed a nocturnal prolactin (PRL) surge on day 8, 5-HIAA levels were very high compared to those that did not, or compared to those on day 16, which had chronic low PRL levels. DOPAC levels were not significantly different in the 3 groups. Perfusion of medial basal hypothalamic (MBH) fragments taken from mother rats on day 8 of pregnancy during the PRL surge spontaneously released more DA or 5-HT than did fragments taken on day 16 at the same time of day. These results suggest that serotonergic activity in the MBH is higher on day 8 of pregnancy, in parallel with the occurrence of PRL surges, than on day 16 when no surges are present. Dopaminergic activity, as measured by DOPAC levels in push-pull samples, does not appear to be different between the two days.

To determine if reported reductions of regional cerebral metabolic rates for glucose (rCMRglc) induced by the 5-HT agent metachlorophenylpiperazine (MCPP) (2.5 mg/kg) are due to a presynaptic action, 3-month old Fischer-344 rats were given parachloroamphetamine (PCA), a serotonin neurotoxin, and rCMRglc was measured 1 or 3 weeks later with the quantitative autoradiographic [14C]2-deoxyglucose procedure in 74 brain regions after administering saline, MCPP or other drugs. PCA alone increased rCMRglc significantly only in the raphe nuclei and in visual structures (visual cortex, lateral geniculate, superior colliculus). MCPP alone reduced rCMRglc in 75% of the regions studied. In PCA-lesioned rats, metabolic responses to MCPP 2.5 mg/kg were virtually abolished and rCMRglc was increased in interanteromedial and centrolateral thalamic nuclei. rCMRglc responses to quipazine, a postsynaptic serotonin agonist, and to arecoline and bromocriptine, cholinergic and dopaminergic agonists, were unchanged by PCA-pretreatment. Selective abolition by PCA of the metabolic response to MCPP confirms that MCPP, at the dose studied, reduces rCMRglc in the forebrain via a presynaptic mechanism and that postsynaptic serotonergic function is not altered by PCA.

Norepinephrine, epinephrine, dopamine, serotonin and their major metabolites were measured by high-performance liquid chromatography with electrochemical detection in 49 regions of the human brain. The regional distribution of the different monoamines in the subcortical areas was similar to previous reports. We report here the distribution pattern of the 4 monoamines observed in the cerebral cortex. Regional differences in concentration were observed for norepinephrine, epinephrine and serotonin, with high concentrations in the frontal and parietal regions. However, no regional difference in dopamine concentrations was detected. The possible role of norepinephrine and serotonin as conventional transmitters, and of dopamine and epinephrine as neurotransmission modulators is discussed.

Microinjection of the indirect GABAA antagonist, picrotoxin, or the mu opioid agonist, Tyr-D-Ala-Gly-NMe-Phe-Gly-ol (DAGO), into the ventral pallidum and substantia innominata (VP/SI) increases locomotor activity in rats. The VP/SI has direct and indirect projections to the region of the ventral mesencephalon containing dopamine perikarya, and to certain dopamine terminal fields, including the nucleus accumbens. Thus, it is possible that modulation of the mesocorticolimbic dopamine system by pharmacological stimulation in the VP/SI may play a role in the locomotor stimulant response. It was shown that pretreatment with dopamine receptor antagonists, either peripherally or microinjected into the nucleus accumbens significantly attenuated the motor stimulant effect of DAGO or picrotoxin injection into the VP/SI. Injection of either picrotoxin or DAGO into the VP/SI increased the levels of dopamine metabolites in the nucleus accumbens and prefrontal cortex. Thus, the motor stimulant response following pharmacological stimulation of the VP/SI appears to be mediated by increased dopamine neurotransmission via feedback mechanisms to the mesocorticolimbic dopamine system.

To clarify the pharmacological mechanism by which ceruletide affects involuntary movements, we used 20-h food-deprived mice to examine the acute effects of ceruletide (600 micrograms/kg, i.p.) on the histochemistry of striatal dopaminergic and serotonergic systems. The latter was unchanged but a reduction in catecholamine fluorescence was seen which was restricted to the ventrolateral (VL) portion of the striatum. Biochemical assays also indicated decreased levels of dopamine (DA) and its metabolites in this restricted region of the striatum with little or no change in noradrenaline, serotonin or their metabolites. In all regions examined, except the dorsomedial part of the mid-striatum, the ratio of dopamine metabolites to dopamine was higher in the ceruletide-treated group than in controls, suggesting increased DA release. Further pharmacological experiments showed that, compared to results in mice receiving only ceruletide: the ceruletide-induced decreases in DA and dihydroxyphenylacetic acid (DOPAC) in VL were less after alpha-methyl-p-tyrosine treatment; ceruletide caused no significant decrease in either DA or DOPAC after pargyline pretreatment, although the low levels of homovanillic acid (HVA) were still further significantly reduced; and the ceruletide-induced decrease of DA was reduced, that of DOPAC was abolished and that of HVA enhanced by nomifensine pretreatment. These results suggested that ceruletide might induce a more rapid degradation of DA in VL and increased efflux of HVA through the blood-brain barrier. This evidence suggests that ceruletide has a regionally specific effect on the striatal dopaminergic system which may relate to the amelioration of involuntary movements.

The excitatory effects of adrenoceptor agonists on ventral horn cells were compared using an extracellular recording technique in spinal cord slices isolated from non-treated and 6-hydroxydopamine (6-OHDA)-treated rats (intracisternally 14 days previously). In spinal cord slices isolated from 6-OHDA-treated rats, the concentration-response curves for the alpha 1-adrenoceptor-mediated facilitatory effects produced by noradrenaline and phenylephrine but not those produced by methoxamine and isoproterenol were shifted to the left. 6-OHDA pretreatment decreased the level and uptake of noradrenaline and increased the number of [3H]prazosin binding sites in the spinal cord. These results suggest that in 6-OHDA-induced denervation, functional supersensitivity of the alpha 1-adrenergic system in the spinal ventral horn is due to absence of an uptake system, and not to postsynaptic change.

The purpose of the present experiment was to determine the effects of lesions of cholinergic neurons originating from the nucleus basalis magnocellularis (NBM), alone or in combination with central serotonin depletion, on learning and memory in rats trained in the Stone 14-unit T-maze--a complex, positively-reinforced spatial discrimination task. Lesion of cholinergic neurons within the NBM was accomplished by bilateral infusion of ibotenic acid. Serotonin depletion was accomplished by the systemic administration of p-chloroamphetamine (PCA). The results show that PCA-induced serotonin depletion enhanced learning. This effect was completely prevented by NBM lesions, despite the fact that NBM lesions alone did not affect the performance of rats in this task. The results of this study support the view that the cholinergic and serotonergic systems may functionally interact in learning and memory processes. The significance of this interaction in the etiology and treatment of dementia should be further investigated.

Extracellular levels of serotonin (5-HT), dopamine (DA) and their major metabolites 5-hydroxyindoleacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA), were measured in the lateral hypothalamus of awake, freely moving rats using microdialysis combined with HPLC and electrochemical detection. To characterize the factors which control 5-HT release, the effects of various drugs were assessed. TTX had a reversible inhibitory effect on the basal levels of 5-HT, 5-HIAA, DOPAC and HVA. Infusion of K+ concomitantly increased 5-HT and DA and decreased 5-HIAA and HVA. Imipramine increased extracellular levels of 5-HT and DA and decreased 5-HIAA levels; this effect was TTX-sensitive. Systemic pargyline increased extracellular 5-HT and markedly decreased the metabolic levels. Pargyline pretreatment in the presence of imipramine, infused through the dialysis probe, slowly increased 5-HT levels above that produced by the reuptake blocker alone. Infusion with AMPH produced a dramatic, TTX-insensitive, increase in 5-HT and DA and a decrease in the metabolic levels. These results provide evidence that (1) basal release of 5-HT in the lateral hypothalamus results from neuronal activity, (2) the metabolites in the extracellular fluid derive primarily from intracellular monoamine oxidase (MAO) activity, (3) 5-HT is mainly removed from the extracellular space by a reuptake mechanism, with minimal contribution of an extracellular MAO, and (4) the AMPH-evoked release of 5-HT and DA is a Na+ channel-independent process.

Sexual behaviors, including singing, in male zebra finches are under the combined control of androgens and estrogens. Treating castrates with androstenedione (AE), a hormone which provides both androgenic and estrogenic metabolites, restores catecholamine (CA; i.e., norepinephrine (NE) and dopamine (DA] function in brain areas known to be involved in the control of these behaviors. Since these behaviors can only be activated by the combined action of androgens and estrogens, the present study determined whether estrogen alone, androgen alone, or only their combination would restore CA function in these brain areas. Males were castrated for at least three weeks and then received one of three hormone implants: (1) estradiol (E) alone, (2) dihydrotestosterone (DHT) alone, or (3) E + DHT. Each male was then housed with a female for at least one week. Levels of NE, DA, epinephrine, serotonin and the latter's primary metabolite, 5-hydroxyindoleacetic acid, were measured in 3 hypothalamic, one auditory and 6 vocal control areas in their brains. NE and DA turnover in these areas were also estimated using alpha-methylparatyrosine. CA function proved to be hormone sensitive in 64% of the comparisons in the three hypothalamic and six vocal control nuclei examined. As expected, the treatment which provided both estrogenic + androgenic stimulation (E + DHT) restored CA function in all of these cases. Although E + DHT restored CA function in these areas, only 22% required both estrogenic + androgenic stimulation to restore normal CA function. For 57% of the comparisons, treatment with E alone also restored normal function, while in the remaining 22%, DHT alone was sufficient. All hormone-induced changes in noradrenergic neurotransmission were estrogen dependent; while modulation of DA function was much more variable, and frequently androgen dependent. To the best of our knowledge, this is the first time that these types of functional differences in the role of estrogen versus androgen in the modulation of neurotransmitter systems has been demonstrated.

Recently, we reported bilateral increases in striatal neurotensin (NT) levels following unilateral 6-hydroxydopamine lesion of the nigrostriatal dopaminergic pathway. In the present study, the effect of unilateral striatal lesions with quinolinic acid (QA, 300 nmol) or ibotenic acid (IBO, 130 nmol) on striatal NT levels and binding site densities were analyzed in order to investigate other possible regulations of NT systems. QA and IBO injection decreased gamma-aminobutyric acid (GABA) levels and [125I]iodosulpride (a specific D2 receptor antagonist) binding site densities in the lesioned striatum, indicating degeneration of striatal intrinsic neurons. Striatal dopaminergic terminals were not altered by QA as shown by the lack of changes in [3H]dihydrotetrabenazine [( 3H]TBZOH, a specific ligand of the vesicular monoamine transporter) binding site densities. Moreover, QA lesion induced an increase in NT levels and a decrease in NT binding sites in the lesioned striatum without any change in the contralateral structure. In contrast to QA, IBO might destroy a certain proportion of dopaminergic terminals in the lesioned striatum, as shown by a 54% decrease in [3H]TBZOH binding. Furthermore, IBO lesion enhanced striatal NT levels bilaterally, while NT binding sites decreased in the lesioned striatum and increased in the contralateral side. The present results suggest that not only dopaminergic neurons but also striatal intrinsic neurons may control NT systems in the striatum.

Male CF-1 mice aged 22 months showed approximately the same level of motor activity and aggressive behavior as 3-month-old mice under control (no stress) conditions, or 45 min following cold swim stress. Increasing brain catecholamine activity by dietary L-tyrosine treatment had no effect on these two age groups either under control conditions or after stress. In contrast, 30-month-old mice showed lower motor activity under control conditions which was raised significantly by supplementation of the diet with L-tyrosine. However, marked reductions in activity and aggression following stress were observed in the 30-month-old animals and these deficits were not reversed by L-tyrosine treatment prior to stress. Reduction in motor activity was greatest in stressed, 30-month-old mice on L-tyrosine supplemented diets. Compared to 3-month-old mice, the 30-month-old animals had lower brain tyrosine following dietary L-tyrosine treatment, lower brain tryptophan, norepinephrine (NE), dopamine (DA) and DOPAC, but higher HVA, serotonin (5-HT) and 5-HIAA levels. Under both control (no stress) and stress conditions, L-tyrosine pretreatment decreased brain 5-HT in the young animals, but increased 5-HT in the old mice. After stress the 30-month-old animals evidenced only slight increases in levels of blood corticosterone. Brain tyrosine was reduced by stress in the young animals but increased by stress in the old animals. Stress-induced decreases in brain NE and increases in serotonin and 5-HIAA levels were observed in both age groups. These results are consistent with hypotheses concerning age-related alterations in brain monoamine functions and adrenocortical control mechanisms.

An in vitro preparation of the trout saccular macula, containing a large number of hair cells, served as a potential source of neurotransmitter(s) released at the acousticolateralis hair cell-afferent nerve synapse. An in vitro preparation of the saccular nerve, maintained in parallel, served to indicate the potential neural contribution to overall release from the macula. Efflux of 27 primary amine-containing compounds from the macula and nerve fractions was monitored by cation-exchange HPLC with fluorescence detection, and release by 53.5 mM potassium was determined at 1.45 mM calcium, 0.35 mM magnesium or 0 mM calcium, 10.1 mM magnesium. Taurine was released from the saccular macula in the greatest amount, accounting for 72% of the total evoked release of primary amine-containing compounds. Its release was calcium dependent and its time course prolonged. The contribution by myelinated nerve and associated Schwann cells within the macula to overall release of taurine from the macula in the presence of calcium, as determined from the saccular nerve preparation, was only 2%. Other components specifically released from the macula included ethanolamine, phosphoserine, beta-alanine, and glycine. Glutamate and aspartate were released from both the macula and saccular nerve fractions by potassium in the presence of calcium and in a ratio of 6:1 (glutamate:aspartate) for the macula and 7.5:1 for the nerve. The release of aspartate, but not that of glutamate, was lowered in saline containing 0 mM calcium, 10.1 mM magnesium. The calculated contribution from neural elements to overall release from the macula was 10% for aspartate and 18% for glutamate. These studies demonstrate that both the macula and saccular nerve fractions release the 'excitatory neurotransmitter' candidates aspartate and glutamate. Calcium-dependent, potassium-evoked release of taurine appears to be specific to the hair cell-supporting cell population of the saccular macula, and taurine may, therefore, be involved directly or indirectly in hair cell neurotransmission in labyrinthine organs. This study represents the first detailed biochemical characterization of efflux and release for an in vitro hair cell system of relatively high purity with respect to hair cells.

The studies were performed on operation material from 17- to 63-year-old patients and on fetuses at 19-23 weeks gestational age. Formaldehyde histofluorescence showed the presence of numerous perivascular adrenergic nerves around pial and intracerebral vessels, the carotid system being better supplied than the vertebral system. Cholinergic nerves, visualized by the cholinesterase technique, followed the adrenergic fibers in the plexus formations of the pial arterial system. Histamine-containing mast cells, often with a perivascular distribution, were located with the o-phthaldiadehyde method. Transmural electrical stimulation of the perivascular nerves contracted isolated pieces of pial arteries in a frequency-dependent manner, and the response was inhibited by the adrenergic nerve blocking agent, guanethidine. On the basis of the relative potency of various amines and related compounds in producing a motor response of isolated pial arteries, and the mode of inhibition caused by specific antagonists, various amine receptors could be demonstrated: adrenergic alpha-receptors (mediating contraction) and beta-receptors (dilation), cholinergic muscarinic receptors (dilation) and histamine H2-receptors (mediating dilation). Thus, the amine mechanisms demonstrated in human brain vessels appear to be principally the same of those shown in more extensive studies on laboratory animals.

Brains from breed and age-matched canines stored at -80 degrees C for between 3 and 44 months showed a time-dependent decline in the concentration of norepinephrine in the amygdala and dopamine and norepinephrine in the caudate. No changes were seen in the density or ligand affinities of prazosin or spiperone binding sites in the same areas nor were there changes in quinuclidinyl benzylate binding sites in the frontal cortex. The changes in dopamine concentrations in the caudate were not accompanied by changes in the concentrations of dopamine metabolites. The chromatograms from which the dopamine and norepinephrine concentrations were estimated contained several unidentified, amperometrically detectable, extraneous peaks which increased in size in the older tissue samples. These results suggest that the decline in dopamine and norepinephrine concentrations was not the result of enzymatic breakdown, but probably the result of chemical decomposition. These findings have significance for the measurement of dopamine and norepinephrine concentrations in autopsied brains kept frozen in storage.

The effects of hypoxia FiO2 = 0.10 on concentration of biogenic amines in specific brainstem nuclear groups were investigated in 3-and 21-day-old rabbits. The rabbit pups were confined to temperature-controlled water-jacketed chambers and exposed to 6h of 21% O2 or to one of 3 combinations of 21% O2 and 10% O2. These 3 combinations were either intermittent hypoxia, or 4 h of normoxia followed by 2 h constant hypoxia, or 2 h of hypoxia followed by recovery for 4 h in normoxia. Radioenzymatic assays were used to determine the concentration of dopamine, norepinephrine and serotonin in the following brainstem nuclei: substantia nigra, locus coeruleus, dorsal raphe and the nucleus reticularis pontis oralis. Compared with control, hypoxia did not affect dopamine levels at either age. The concentration of norepinephrine was inconsistently affected by hypoxia at either age. In contrast, in the 3-day-old rabbits serotonin was consistently reduced in each of the nuclei. In the 21-day-old rabbits, serotonin was either unchanged or increased following hypoxia. Our results show that hypoxia alters the concentration of serotonin in an age-specific manner. This change in serotonin concentration may reflect altered serotonin metabolism and suggests a possible mechanism by which hypoxia disrupts physiologic homeostasis in newborns.

We investigated the effect of aminophylline on thiopental sleep-times and monoamine neurotransmitter turnover rates in discrete brain areas. Aminophylline-treated rats had shorter thiopental sleep-times than saline-treated controls. Noradrenergic neurotransmission was greater following aminophylline treatment in thiopental-anesthetized rats in all brain areas while turnover in other monoaminergic pathways was unchanged. These data suggest that acute aminophylline treatment increases central noradrenergic neurotransmission which pharmacodynamically diminishes the hypnotic response to thiopental.

Practical utilization of in vivo electrochemistry for brain studies has been impeded by difficulties with specificity and quantitative measurements. Studies in brain slices combined with similar data from intact animals have provided important new information on the nature of the electrochemical studies. Using the enzyme ascorbic acid oxidase (AAO), the primary signal contribution has been calculated to come from ascorbic acid. By inhibiting monoamine oxidase activity with pargyline, the second most important contributor in caudate extracellular fluid is postulated to be 3,4-dihydroxyphenylacetic acid. These species are calculated to constitute over 93% of the observed oxidation current in rat caudate extracellular fluid.

In vivo electrochemical methods were employed to study the potassium (K+)-evoked release of monoamines from the cerebellum of the chloral hydrate anesthetized rat. K+-evoked releases were elicited using micropipette-Nafion-coated graphite epoxy electrode arrays in the granule/Purkinje cell layer, molecular layer, and white matter. These recorded releases were generally found to be reversible, moderately dose-dependent, and reproducible. However, the temporal dynamics of the releases were different for the cell layer versus molecular layer records. Releases were infrequently observed in cerebellar white matter, an area which is relatively devoid of monoamine containing terminals. The signals recorded from the cell and molecular layers were significantly attenuated by pretreatment with the selective noradrenergic neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4). Local pretreatment with nomifensine, a potent catecholamine reuptake blocker, significantly prolonged the K+-evoked signals observed in both the granule/Purkinje cell and molecular layers. These data, taken together with earlier reports on the electrophysiological responses to activation of cerebellar noradrenergic inputs, support the conjecture that in vivo electrochemical recording methods have the sensitivity and spatial resolution for studies of functional monoamine release from brain regions that have a diffuse or laminated monoamine innervation.

The stratification of principal fiber systems affiliated with the developing neocortex has been analyzed by means of HRP tracing methods, monoamine histofluorescence and silver impregnations in mouse embryos ranging from the 15th to 16th embryonic day (E15/16) to the end of gestation (E19 = the day of birth). As early as E15/16 a fiber stratum divides the subplate and marks the inferior boundary of the developing cortex. Axons coursing in this fiber plane, termed the external sagittal stratum (ESS), include components of at least 5 identifiable systems: thalamocortical, corticothalamic, ipsilateral corticocortical, callosal and monoaminergic. The neocortical afferents of extrinsic origin, i.e., the thalamocortical, callosal and monoaminergic systems, cross the intermediate zone from their separate directions and converge upon the ESS. After a variable course through this stratum, single fibers ascend from their parent fascicles to ramify densely in the cortical subplate (CSB). Fibers of each of the extrinsic afferent systems mingle with each other and with locally arising axons within the CSB. Axons of the monoaminergic projection as well as fibers of the thalamic projection cross the cortical plate to ramify in the marginal zone. Other axons apparently of local intracortical origin course tangentially through the cortical plate. Otherwise, the cortical plate is devoid of proliferating axons at this early developmental stage. The set of observations illustrates the existence of sharply defined boundaries between axon-rich and axon-poor strata of the developing neocortex. These boundaries also compartmentalize postmigratory neurons with respect to their state of differentiation.

Behavioural, neurochemical and histopathological changes induced by systemic injection of kainic acid were investigated at various doses of the neurotoxin (3, 6 and 10 mg/kg s.c.). There was a positive correlation between the dose of kainic acid and the extent of both the acute neurochemical changes 3 h after the injection (increases of 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid levels and a decrease in noradrenaline levels in all brain regions investigated), the acute histopathological changes (shrinkage and condensation of nerve cells and brain oedema in the entire forebrain) and the extent of behavioural alterations (immobility, 'wet dog shakes' and limbic seizures). However, the slope of the dose-response curves was very steep. Late and irreversible alterations included losses of the enzyme markers glutamic acid decarboxylase and choline acetyltransferase and, histopathologically, incomplete parenchymal necrosis and haemorrhages. These changes, however, were restricted to a few brain regions, the most important being the hippocampus, amygdala, entorhinal and pyriform cortex, and olfactory bulb, and they were seen only in animals which had undergone severe convulsions. It is suggested that the irreversible brain lesions in this animal model of limbic (temporal lobe) epilepsy are not solely induced by a direct action of kainic acid, but may be caused--at least in part--by additional, secondary pathogenetic mechanisms.

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg/kg s.c. for 5 days) to mice resulted in complete abolishment of strychnine seizure and of the tonic phase of the maximal electroshock response. Bicuculline and picrotoxin convulsions were not significantly affected by MPTP treatment. The severity of the pentylenetetrazole seizures was mildly, but significantly affected in the protective way. MPTP depleted neostriatal dopamine and its metabolites, together with hippocampal norepinephrine. No nigral neuronal loss was detected histologically. Strychnine seizures and the tonic phase of the maximal electroshock response are thought to depend mostly on hindbrain (bulbo-spinal) structures. Thus, these experiments suggest that a caudally projecting system originates from the substantia nigra, pars compacta, and/or locus coeruleus, controlling seizures that involve bulbo-spinal centers. While neostriatal dopamine depletion offers a good index of seizure resistance, its role in the protection from seizures remains to be established.

We studied the effects of systemic injections of monoamine depletors, enhancers or receptor blockers on electroacupuncture analgesia (EAA) in mice. The following results emerged. (i) EAA is reduced by depletors of monoamines (tetrabenazine, TBZ depletes all monoamines; para-chlorophenylalanine, PCPA depletes serotonin; alpha-methyl-para-tyrosine, AMPT depletes catecholamines). However, depletion of noradrenaline and increase of serotonin by disulfiram enhances EAA. (ii) Replacement of depleted monoamines after TBZ treatment by their precursors (5-HTP or L-DOPA) restores EAA. (iii) EAA is enhanced by potentiating serotonin and dopamine by probenecid. EAA is also enhanced by the administration of monoamine precursors (L-DOPA for dopamine, 5-HTP for serotonin). The dopamine receptor stimulator, apomorphine, reduces EAA. (iv) EAA is also reduced by receptor blockade of catecholamines (by haloperidol), or blockade of noradrenaline (by yohimbine) or serotonin (by cinanserin). However, blockade of dopamine by pimozide has no significant effect on EAA. There are two main conclusions: (i) EAA results are similar to those previously reported for SPA for all drugs except apomorphine and pimozide; and (ii) EAA shows consistent results only with manipulations of serotonin: the data indicating that EAA (at 200 Hz) is mediated by serotonin. Since previous studies show that raphe or DLF (dorsolateral fasciculus) lesions abolish EAA, we postulate that descending axons from raphe release serotonin to inhibit trigeminal or spinal cord nociception during EAA.

The concentrations of bioamines and their metabolites have been determined in March and April during arousal from hibernation in the cerebral cortex of the little brown bat (Myotis lucifugus). The patterns during arousal for dopamine and serotonin (5-HT) were similar with a significant fall in concentrations by 1 h of arousal, and an inverse relationship with their respective metabolites, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindolacetic acid (5-HIAA). This suggests an acute release and metabolism of these bioamines with onset of arousal. During arousal, cerebral cortical concentrations of norepinephrine (NE) were not significantly changed. Levels of homovanillic acid were markedly depressed during hibernation and rose acutely with arousal. After arousal and 4 days of feeding in April, there was an increase in all bioamines and their metabolites studied except for NE. Of note is the marked decrease in the hibernating level of 5-HT and increase in its metabolite 5-HIAA from March to April, which may herald the natural termination of hibernation. Our results suggest that the brain of hibernators undergoes complex changes in the modulation of neurotransmitter systems which are consistent with both down- and up-regulation of neuronal activity in the maintenance of hibernation and the initiation of the arousal process.

The neurobehavioral responsiveness of two strains of rats, Fischer-344 (CDF) and Sprague-Dawley (CD), to a repeated foot-shock-induced analgesia (FSIA) stress was compared in this study. Rats were either restrained or freely moving during shock presentation (sham controls were exposed to the shock environment only). The foot-shock (15-s, 1.5-mA scrambled electric shock) was observed to induce analgesia in the CDF, but not the CD strain following acute presentation; analgesia was evaluated using time for tail-withdrawal from hot water (55 degrees C). Both strains exhibited an analgesic response when latency to tail withdrawal was evaluated just prior to daily FSIA presentations over 15 total sessions indicating that these rat strains were behaviorally conditioned to this repeated stressor. However, the levels of conditioned analgesic responses to foot-shock were: greater in the CDF and most evident when rats were restrained on the shock-grid while being administered the foot-shock. All rats were quickly sacrificed following the 15th conditioning session to determine the effects of this stressor on neurotransmitter and neuroendocrine function in both strains of rat. Experimental subjects were exposed to the shock grid but not shocked during this last session. The following was found: plasma corticosterone (CORT) and prolactin levels and adrenal CORT levels were significantly increased by repeated stress in the CDF strain; only plasma CORT levels were elevated in the CD rat; pituitary immunoreactive beta-endorphin levels were significantly higher (+46%) amongst all experimental groups in the CDF strain, but stress was not observed to alter peptide steady-state levels in either strain; dopamine (DA), 5-hydroxytryptamine and metabolites (5-hydroxyindoleacetic acid and dihydroxyphenylacetic acid) levels were generally higher in the hypothalamus and frontal cortex of the CDF rat but turnover rates (implied from metabolite/amine ratios) indicated that these systems were more sluggish in this rat strain; hypothalamic DA turnover was significantly attenuated by repeated FSIA + restraint in both strains, but the dynamics of this effect appeared to be different between rat strains; and frontal cortex 5-HT turnover was significantly elevated by repeated FSIA + restraint in only the CDF rat. This research indicates that the CDF rat is extremely sensitive to an acute FSIA stress and it is less able than the CD rat to adapt to repeated presentation of this stress.

Subcutaneous administration of methylmercury (MeHg) to rats during early postnatal development resulted in movement and postural disorders by day 22-24. Tissue concentrations of norepinephrine (NE), serotonin (5-HT), dopamine (DA) and selected metabolites were measured in the cerebral cortex, spinal cord and caudate-putamen at the onset of neurological impairment and at two subclinical stages of toxicity. In the cerebral cortex there was a significant increase in tissue concentrations of 5-HT (54-81%) and 5-hydroxyindoleacetic acid (HIAA, 133-178%) at the onset of neurological impairment. Similar increases were detected in the spinal cord for 5-HT (19-43%) and HIAA (98-123%) as well as an increase in the concentration of NE (42-51%). In the caudate-putamen there were significant increases in the concentrations of NE (98-116%), HIAA (108-124%) and DA (28-29%) with a significant decrease in the concentration of 3,4-dihydroxyphenylacetic acid (DOPAC, 20-27%); however, tissue levels of homovanillic acid (HVA) did not change significantly. Many of these changes were detected at subclinical stages of MeHg toxicity. The ratio of HIAA/5-HT, which is frequently used as an estimate of turnover for 5-HT, was significantly increased in all 3 tissues at the onset of neurological impairment (38-94%) and at one subclinical stage (47-114%). The ratio of (DOPAC + HVA)/DA was significantly decreased in caudate-putamen at all 3 stages of toxicity (18-40%). These changes indicate altered metabolism in aromatic amine systems in the developing central nervous system during the pathogenesis of MeHg-induced movement and postural disorder.

The content and turnover of dopamine, norepinephrine and 5-hydroxytryptamine (serotonin), and the content of their respective major metabolites were evaluated in 19 discrete brain areas of rats exposed to conditioned emotional response (CER), and in control groups which received either equivalent yoked shock (shock only) or compound stimulus presentation (tone only). On test day, CER animals suppressed responding and exhibited forms of emotional behavior after presentation of the conditioned stimulus (CS); while shock only and tone only control groups, and CER animals which received an acute dose of diazepam prior to testing, did not suppress. Few changes were observed in content of the biogenic amines or their metabolites, suggesting that the behavioral manipulations were acting within normal physiological limits. On the other hand, numerous changes were observed in the utilization of the 3 biogenic monoamines, which were correlated with the conditioning-anxiety (comparisons of CER vs shock only) and the shock history (comparison of shock only vs tone only). These observations are consistent with putative neural pathways in the frontal cortex, septum, nucleus accumbens, amygdala, striatum, hippocampus and brain stem (which utilize specific monoamines), and with discrete brain areas which have been implicated in classical conditioning and CER-related phenomena. These observations suggest roles for biogenic monoamines in mediating or responding to the classical conditioning and emotional components of the paradigm.