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Previously, we have demonstrated that pressure-ejected application of angiotensin II and losartan, an angiotensin AT1 receptor antagonist, onto some neurons in the anterior hypothalamic area (AHA) of the rat increases and decreases, respectively, the basal firing rate of the neurons. To investigate possible participation of these AHA neurons in the brain angiotensin system, we examined whether intracerebroventricular injection of the angiotensin AT1 receptor antagonist losartan inhibits the neuronal activity of angiotensin II-sensitive neurons via GABA inputs in the AHA of rats. Intracerebroventricular injection of losartan decreased the firing rate of AHA angiotensin II-sensitive neurons. However, the intracerebroventricular injection of losartan did not affect the increase in firing rate of AHA angiotensin II-sensitive neurons induced by pressure application of angiotensin II onto the same neurons, although losartan similarly injected abolished the increase in firing rate of AHA angiotensin II-sensitive neurons induced by intracerebroventricular injection of angiotensin II. The losartan-induced decrease of unit firing in AHA neurons was abolished by pressure application of the GABAA receptor antagonist bicuculline onto the same neurons. Bicuculline itself did not affect the basal firing rate of AHA neurons. These findings suggest that intracerebroventricular injection of losartan inhibits AHA angiotensin II-sensitive neurons via GABA inputs to the neurons.

We have previously demonstrated that some neurons in the anterior hypothalamic area (AHA) of rats are tonically activated by endogenous angiotensins and that reactivities of these neurons to angiotensin II are enhanced in 15- to 16-week-old spontaneously hypertensive rats (SHR). To investigate whether the enhanced reactivity of SHR AHA neurons to angiotensin II is secondary to raised blood pressure, we examined whether the enhanced reactivity to angiotensin II also occurs in prehypertensive SHR. We also examined whether reactivities of AHA angiotensin II-sensitive neurons to intracerebroventricular hypertonic saline are enhanced in prehypertensive SHR, since intracerebroventricular injection of hypertonic saline increases the firing rate of AHA neurons via release of angiotensins at AHA neuron levels. Male 4-week-old SHR and age-matched Wistar Kyoto rats (WKY) were used in this study. There was no difference in systolic blood pressure between both rats. They were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Pressure application of angiotensin II onto some AHA neurons increased their firing rate. The basal firing rate of angiotensin II-sensitive neurons was increased in SHR as compared with WKY. The increase of unit firing by angiotenisn II was enhanced in SHR as compared with WKY. Intracerebroventricular injection of hypertonic saline increased the firing rate of AHA angiotensin II-sensitive neurons. The average threshold sodium concentration for the saline-induced increase of neural firing was lower in SHR than in WKY. These findings demonstrate that basal activities and responsiveness to angiotensin II in AHA angiotensin II-sensitive neurons are enhanced in prehypertensive SHR as compared with age-matched WKY. In addition, these findings indicate that central saline-induced activation of AHA angiotensin II-sensitive neurons is also enhanced in SHR. It appears that the enhanced reactivity of SHR AHA neurons to angiotensin II occurs primarily in nature but not secondarily to raised blood pressure in SHR.

It has been suggested that neurons in the hypothalamus respond to baroreflex activation and deactivation. In this study, we examined whether angiotensin II-sensitive neurons in the anterior hypothalamic area (AHA) respond to baroreflex activation and deactivation, and which neurotransmitters are involved in mediating the baroreflex responses. Male Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Increases in blood pressure induced by intravenous phenylephrine completely inhibited the firing of AHA angiotensin II-sensitive neurons. The phenylephrine-induced inhibition of neuronal firing was blocked and enhanced by the pressure application of bicuculline and nipecotic acid, respectively, onto the same neurons. In contrast, decreases in blood pressure induced by intravenous nitroprusside increased the firing of angiotensin II-sensitive neurons. The nitroprusside-induced increase of neuronal firing was blocked by the pressure application of losartan onto the same neurons. These findings suggest that angiotensin II-sensitive neurons in the AHA respond to blood pressure changes via gamma-aminobutyric acid and angiotensins in rats.

We have previously demonstrated that pressure application of the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) onto some neurons in the anterior hypothalamic area of rats increases neural activity in vivo and that this PKC activation-induced increase of neural activity is enhanced in spontaneously hypertensive rats (SHR), an animal model for genetic hypertension. Activation of PKC increases expression of the c-fos gene, an important transcription factor and proto-oncogene thought to be a marker of neural activity. To evaluate PKC isoforms responsible for neural activation, we examined which isoforms of PKC are involved in the PKC activation-induced c-fos gene expression in neuronal cultures of Wistar rat and spontaneously hypertensive rat (SHR) brains. PMA increased c-fos gene expression in neuronal cultures of Wistar rat brain and the PMA-induced c-fos gene expression was inhibited by the PKC inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7). The PKCalpha,beta,gamma activator thymeleatoxin also increased c-fos gene expression, while the PKCdelta,epsilon activator ingenol did not affect it. In addition, the PMA-induced c-fos gene expression was inhibited by PKCbetaantisense oligonucleotides (AON) but not by PKCalpha and PKCgammaAONs. In SHR brain neuronal cultures, the PMA-induced c-fos gene expression was enhanced as compared with that of Wistar Kyoto rats (WKY), while basal c-fos gene expression was almost the same in both neuronal cultures. The enhancement of PMA-induced c-fos gene expression in SHR brain cultures was abolished by PKCbetaAON. These findings suggest that in rat brain neuronal cultures, PMA increases c-fos gene expression via activation of PKC and that PKCbetaisoforms are partly involved in the PMA-induced c-fos gene expression. In neuronal cultures of SHR brain, it appears that the PMA-induced c-fos gene expression is also enhanced via PKCbeta.

We have previously reported that some neurons in the anterior hypothalamic area (AHA) are tonically activated by endogenous angiotensins in rats and that activities of these angiotensin II-sensitive neurons in the AHA are enhanced in spontaneously hypertensive rats (SHR). In addition, neural activations induced by both angiotensin II and glutamate were enhanced in the AHA of SHR. In this study, we examined whether intracellular neural activation mechanisms via protein kinase C (PKC) and a potassium channel are altered in angiotensin II-sensitive neurons in the AHA of SHR. Male 15- to 16-week-old SHR and age-matched Wistar-Kyoto rats (WKY) and Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Pressure application of the PKC activator phorbol 12-myristate 13-acetate (PMA) onto angiotensin II-sensitive neurons in the AHA of Wistar rats increased their firing rate. The increase of unit activity by PMA was inhibited by the potent inhibitor of PKC, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), but not by the weak PKC inhibitor, N-(2-guanidinoethyl)-5-isoquinolinesulfonamide hydrochloride (HA1004). The increase of unit firing by PMA was enhanced in SHR as compared with WKY. Pressure application of H-7 alone decreased the basal firing activity of angiotensin II-sensitive neurons in SHR but not in WKY. HA1004 did not affect the basal firing activity of angiotensin II-sensitive neurons in SHR. Angiotensin II-induced increases of firing rate in AHA neurons were inhibited by H-7 and the inhibition by H-7 was enhanced in SHR as compared with WKY. Pressure application of 4-aminopyridine, a blocker of the transient potassium current, onto angiotensin II-sensitive neurons increased their firing rate and the increase of unit firing rate was almost the same in WKY and SHR. These findings indicate that activation of PKC increases neural activity in angiotensin II-sensitive neurons in the AHA and that this PKC activation-induced increase of neural activity is enhanced in the AHA of SHR. It seems likely that the enhanced PKC activation effect is responsible for the enhanced basal neural activity seen in the AHA of SHR.

We have previously reported that an angiotensin system in the anterior hypothalamic area (AHA) is enhanced in spontaneously hypertensive rats (SHRs) and that this enhancement is involved in hypertension in this strain. In addition, we have reported that some neurons in the AHA are tonically activated by endogenous angiotensins in rats. In this study, we examined whether activities of neurons receiving tonic angiotensinergic inputs in the AHA are enhanced in SHR as compared with those of Wistar Kyoto rats (WKY). Male 15- to 16- or 6-week-old SHR and age-matched WKY were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Pressure application of angiotensin II onto some neurons in the AHA increased their firing rate. The basal firing rate of angiotensin II-sensitive neurons was increased in both 15- to 16- and 6-week-old SHR than in age-matched WKY. The increase of unit firing by angiotenisn II was enhanced in both 15- to 16- and 6-week-old SHR as compared with age-matched WKY. Pressure application of losartan, an angiotensin type 1 (AT1) receptor antagonist, alone decreased the basal firing rate of angiotensin II-sensitive neurons in 15- to 16-week-old SHR and WKY. The decrease of unit firing by losartan was also enhanced in SHR as compared with WKY. Pressure application of glutamate onto angiotensin II-sensitive neurons increased their firing rate and the increase of unit firing by glutamate was enhanced in 15- to 16-week-old SHR as compared with age-matched WKY. These findings suggest that activities of angiotensin II-sensitive neurons in the AHA are enhanced in SHR as compared with WKY. It is possible that the enhanced activity of angiotensin II-sensitive neurons in the AHA of SHR is partly due to enhanced neuronal reactivity to angiotensin II.

We previously demonstrated involvement of the medial amygdaloid nucleus in restraint stress-induced pressor responses in rats. In this study, neuronal perikarya in the medial amygdaloid nucleus of 4-week-old spontaneously hypertensive rats (SHR) were selectively destroyed with ibotenic acid. Bilateral lesions of the medial amygdaloid nucleus attenuated the development of hypertension in SHR. Body weight gain was not different between lesioned and sham-lesioned SHR throughout the experimental periods. These data suggest that neurons in the medial amygdaloid nucleus may be involved in the development of hypertension in SHR.

We previously demonstrated that restraint stress-induced pressor responses were inhibited by bilateral microinjection of muscimol into the rostral part of the ventral zone of the lateral septal area (LSV). The caudal part of the lateral septal area is also reported to be involved in blood pressure regulation. In this study, we examined whether the LSV receives projections from the caudal part of the dorsal zone of the lateral septal area (LSD) in rats. Injections of a fluorescent tracer into the LSV produced maximal retrograde labeling within the LSD. Microinjection of carbachol (10–100 pmol) into the LSD produced a dose-dependent pressor response. The pressor response to carbachol was inhibited by microinjection of muscimol (80 pmol) or 4-DAMP (1 nmol) into the ipsilateral side of the LSV. Microinjection of muscimol (80 pmol) into the LSD also inhibited the pressor response induced by restraint stress. Repeated injections of carbachol (30 pmol) into the LSD produced Fos immunoreactivity in the ipsilateral side of the LSV. These findings suggest that the LSD projects to the LSV and that these projections may be involved in blood pressure increase.

The angiotensin type 1a (AT1a) receptor gene is overexpressed in the brain and peripheral tissues of spontaneously hypertensive rats (SHR). We examined whether there are mutations responsible for overexpression of the AT1a receptor gene in the SHR AT1a receptor promoter region. Genomic DNA was extracted from the livers of SHR and Wistar Kyoto rats (WKY) of Izumo strain (SHR/Izm and WKY/Izm, respectively). Fragments of the AT1a receptor gene promoter region were amplified by polymerase chain reaction (PCR). Amplified fragments were purified by agarose gel electrophoresis, and the purified fragments were cloned using pTBlue T-Vector. Sequence analysis identified one single base mutation unique to the SHR AT1a receptor gene promoter region when compared to that of WKY. The sequence of the mutation site in SHR was the same as that of Sprague Dawley rats. Using an electrophoretic mobility shift assay, we compared gel patterns formed by DNA-protein complexes using ds-oligonucleotides representing region-1624 to-1595 of the SHR and WKY AT1a receptor promoters. There were 3 major similar DNA-protein complexes against WKY and SHR oligonucleotides. In addition, the oligonucleotide bearing the SHR sequence produced an extra band. Promoter/luciferase reporter assay demonstrated that the promoter activity of SHR AT1a receptor promoters (-2050 to +57) was lower than that of WKY. These results suggest that there is one single mutation unique to the SHR AT1a receptor gene promoter region, but that the mutation is not responsible for overexpression of the AT1 a receptor gene in SHR.

Previously, we demonstrated that the rostral part of the ventral zone of the lateral septal area (LSV) was involved in the restraint stress-induced pressor response. It is suggested that there exist acetylcholine receptors responsible for blood pressure increase in the caudal part of the lateral septal area. In this study, we examined whether acetylcholine receptors responsible for pressor responses also exist in the rostral part of the LSV and whether these acetylcholine receptors are involved in the stress-induced pressor response in rats. Microinjection of either carbachol (10–100 pmol) or physostigmine (0.46 and 1.5 nmol) into the LSV caused a dose-dependent increase in blood pressure. The pressor response to carbachol (30 pmol) was inhibited by the M1 antagonist pirenzepine and the M3 antagonist 4-DAMP mustard but not by the M2 antagonist methoctramine injected into the LSV. Bilateral microinjections of the M1/M3 antagonist 4-DAMP (1 nmol) inhibited the restraint stress-induced pressor response. These findings suggest that M1/M3 muscarinic receptors responsible for blood pressure increase exist in the rostral part of the LSV and they are partly involved in the stress-induced pressor response.

1. We previously reported that activation function of mitogen-activated protein kinases (MAPK) is enhanced in aorta strips from both prehypertensive and hypertensive spontaneously hypertensive rats (SHR) and that this enhancement of MAPK activation results from enhanced MAPK activation reactivity to angiotensin (Ang) II in SHR aorta strips. 2. The purpose of the present study was to examine whether the enhanced function of the vascular angiotensin system observed in SHR aorta strips results from genetic alterations of vascular smooth muscle cells from SHR. 3. Basal MAPK activity was within normal limits in cells from 4-week-old SHR, whereas enzyme activity was enhanced in 9-week-old SHR compared with age-matched Wistar-Kyoto (WKY) rats. 4. Mitogen-activated protein kinase activation reactivity to AngII and endothelin-1 was enhanced in 9-week-old SHR cells but not in 4-week-old SHR cells. The enhancement of basal MAPK activity in 9-week-old SHR cells was abolished by a combination of the angiotensin AT(1) receptor antagonist losartan and the endothelin receptor antagonist BQ123. 5. These findings suggest that MAPK activation function in 4-week-old SHR cells is not enhanced. Thus, it appears that factors outside vascular smooth muscle cells are needed for the enhanced MAPK activation observed in 4-week-old SHR aorta strips. In 9-week-old SHR, MAPK activation function is enhanced in cells themselves and this function may, at least in part, contribute to the enhanced MAPK activation observed in SHR aorta strips.

We previously reported that pressure loading of the vascular wall can activate mitogen-activated protein kinases (MAPKs), enzymes believed to be involved in the pathway for cell proliferation, partly via the vascular angiotensin system in isolated perfused rat aorta. In this study, we examined whether cyclic stretching of vascular smooth muscle cells (VSMC) also produces activation of p42 and p44 MAPKs in cultured rat VSMC and whether stretch-induced MAPK activation is mediated via angiotensin and endothelin systems in VSMC. Cyclic stretching of VSMC produced an elongation-dependent and frequency-dependent increase in p42 and p44 MAPK activity. The stretch-induced p42 and p44 MAPK activation was inhibited by the angiotensin receptor antagonist losartan and by the angiotensin-converting enzyme inhibitor, captopril. The MAPK activation was also inhibited by the endothelin receptor antagonist cyclo(D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl) (BQ123) and by the endothelin-converting enzyme inhibitor phosphoramidon. Replacement of medium with culture medium of stretched cells caused MAPK activation, which was inhibited by losartan and BQ123. The results of the present study suggest that cyclic stretching of VSMC can activate p42 and p44 MAPKs and that the MAPK activation is mediated via angiotensin and endothelin systems in VSMC.

Immobilization stress increased the number of neurons with Fos immunoreactivity, mainly in the ventral zone of the rostral part of the lateral septal nucleus (LSV) in rats. Immobilization stress caused an increase in blood pressure, and the stress-induced pressor response was inhibited by the GABA(A) receptor agonist, muscimol (8 and 80 pmol), injected bilaterally into the rostral part of the LSV in a dose-dependent manner. Intracerebroventricular injection of muscimol (16 pmol) did not affect the immobilization stress-induced pressor response. These findings suggest that the rostral part of the LSV is involved in mediation of the stress-induced pressor response.

IgE plays a key role in the pathogenesis of allergic disease. Interleukin (IL) 4 is a potent and critical stimulator of immunoglobulin class switching from IgM to IgE in B cells. IL-4 induces the expression of epsilon germline transcript (epsilonGT), which is critical to initiate IgE production. While searching for molecules that inhibit epsilonGT expression induced by IL-4, we found that polyphenol strictinin, which was isolated from tea leaves, was able to inhibit the IL-4-induced epsilonGT expression in the human B cell line DND39. Strictinin also acted on human peripheral blood mononuclear cells obtained from healthy donors to inhibit IL-4-induced epsilonGT expression. Strictinin demonstrated similar inhibitory activity in peripheral blood mononuclear cells obtained from atopic donors. Interestingly, strictinin decreased ovalbumin-induced IgE production in mice, whereas the production of IgG and IgM was not affected. Furthermore, we found that the IL-4-induced STAT6 tyrosine phosphorylation, which is essential for IL-4-induced epsilonGT expression, was inhibited in DND39 cells upon treatment with strictinin. Taken together, these results suggest that strictinin can inhibit IgE production through the inhibition of IL-4-mediated signaling in B cells.

An overactive brain renin-angiotensin system is one of the factors contributing to the pathogenesis of hypertension in spontaneously hypertensive rats (SHR). We examined brain sites where enhanced activity of an angiotensin system is responsible for the pathogenesis of hypertension in SHR. The angiotensin receptor antagonist, losartan was injected into tissues around rostral parts of the third ventricle in conscious rats. Losartan (0.22 nmol) injected into the anterior hypothalamic area, anterior (AHA) produced a depressor response in SHR but not in Wistar Kyoto rats (WKY). Angiotensin II (0.091-0.91 pmol) injected into the AHA produced a pressor response in both WKY and SHR, and the pressor response to angiotensin II was greater in SHR than that of WKY. Carbachol (3 pmol) injected into the AHA also produced a pressor response in WKY and SHR, and the pressor response to carbachol was almost the same in both strains of rats. Release of angiotensin peptides in the AHA was greater in SHR than that of WKY. These findings suggest that an angiotensin system in the AHA is enhanced and this enhancement of angiotensin system is involved in the maintenance of hypertension in SHR. Both increased pressor reactivity to angiotensin II and increased release of angiotensin peptides in the AHA appear to be related to this enhancement of angiotensin system in SHR.

Regulation mechanisms of the activity of vascular mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, may be altered in hypertension. To examine whether vascular MAP kinase activation mechanisms are altered in hypertension, we measured the activity of MAP kinases in rat aorta strips from spontaneously hypertensive rats (SHR) and from deoxycorticosterone acetate (DOCA)-salt hypertensive rats, and examined whether vascular angiotensin and endothelin systems are responsible for the alteration of MAP kinase activation in these hypertensive models. Endothelium-denuded aorta strips were incubated at 37°C in medium. MAP kinase activity after incubation was increased in rat aorta strips. The MAP kinase activation was greater in 9- and 15-week-old SHR aorta strips than in age-matched Wistar Kyoto rats (WKY) aorta strips. Similarly, MAP kinase activation was enhanced in aorta strips from DOCA-salt hypertensive rats. In aorta strips from these kinds of rats, the angiotensin receptor antagonist, losartan, and the endothelin receptor antagonist, cyclo ( d -α-aspartyl- l -prolyl- d -valyl- l -leucyl- d -tryptophyl) (BQ123), inhibited the MAP kinase activation. The losartan-induced, but not BQ123-induced, inhibition of MAP kinase activation was enhanced in 15-week-old SHR aorta strips, whereas the BQ123-induced, but not losartan-induced, inhibition of MAP kinase activation was enhanced in DOCA-salt hypertensive rat aorta strips. Angiotensin II-induced MAP kinase activation was enhanced in 15-week-old SHR aorta strips, whereas it was depressed in DOCA-salt hypertensive rat aorta strips. These results indicate that MAP kinase activation function is enhanced in aorta strips from both kinds of hypertensive rats. It appears that the enhancement of MAP kinase activation results partly from enhanced vascular angiotensin system in SHR and from enhanced vascular endothelin system in DOCA-salt hypertensive rats.

Vascular hypertrophy occurs during chronic hypertension and contributes to the elevation of peripheral vascular resistance in hypertension. In this study, we examined whether acute pressure overloading of the vascular wall produces activation of mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, in isolated perfused rat aortae, and examined whether the mechanical overloading-induced MAP kinase activation is mediated via the vascular angiotensin system. Aortae were perfused with Tyrode solution. Increases in perfusion pressure caused a pressure-dependent increase in MAP kinase activity in endothelium-intact aortae and in endothelium-denuded aortae. The increase in MAP kinase activity induced by pressure loading was inhibited by the angiotensin receptor antagonist, losartan, the renin inhibitor, pepstatin A, and the angiotensin-converting enzyme inhibitor, captopril. Ca 2+ depletion and the Ca 2+ channel antagonist, nifedipine, did not affect the pressure loading-induced MAP kinase activation. The results of the present study suggest that pressure loading of the vascular wall per se can activate MAP kinases in the vasculature and that the MAP kinase activation is mediated at least partly via the vascular angiotensin system. It seems unlikely that the pressure loading-induced increase in MAP kinase activity is mainly mediated via increases in Ca 2+ influx in vascular cells.

It has been established that deoxycorticosterone acetate (DOCA)-salt hypertensive rats have an overactive brain angiotensin-system. The purpose of the present study was to identify the brain sites showing enhanced angiotensin-system activity responsible for the pathogenesis of hypertension in DOCA-salt hypertensive rats. The angiotensin receptor antagonist, losartan, was injected into brain ventricles or into tissues around the rostral parts of the third ventricle in conscious DOCA-salt hypertensive rats. Losartan (1μg) injection into the lateral ventricle or into the rostral parts of the third ventricle produced a depressor response, whereas the agent did not affect blood pressure when injected into the caudal parts of the third ventricle or into the fourth ventricle. Losartan (0.1μg) injection into the anterior hypothalamic preoptic area, anterior (AHA) produced a depressor response. Angiotensin II (0.1-1ng) injection into the AHA produced a pressor response in sham-operated and DOCA-salt hypertensive rats, and the pressor response to angiotensin II (1ng) was greater in DOCA-salt hypertensive rats than that in sham-operated rats. Release of angiotensin peptides in the AHA was greater in DOCA-salt hypertensive rats than that in sham-operated rats. These findings suggest that the angiotensin-system in the AHA is enhanced, and that this enhancement is involved in the maintenance of hypertension in DOCA-salt hypertensive rats. Both increased pressor reactivity to angiotensin II and increased release of angiotensin peptides in the AHA appear to be related to this enhancement of the angiotensin-system in DOCA-salt hypertensive rats. (Hypertens Res 2000; 23: 109-118)

There are cholinergic inputs responsible for pressor responses in the rostral ventrolateral medulla (RVLM) and stimulation of midbrain central gray (CG) increases arterial pressure via activation of neurons in the RVLM. In this study, we examined whether the CG was involved in mediation of the cholinergic inputs to the RVLM. Male Wistar rats were anesthetized, paralyzed, and artificially ventilated. Unilateral microinjection of L-glutamate into the CG produced a pressor response. Microinjection of the muscarinic receptor antagonist scopolamine into the unilateral RVLM inhibited the pressor response to L-glutamate injected ipsilaterally into the CG, whereas microinjection of the cholinesterase inhibitor physostigmine into the RVLM enhanced it. CG stimulation also enhanced the firing rate of RVLM barosensitive neurons and the enhancement of the firing rate was inhibited by scopolamine iontophoretically applied on neurons. CG injection of L-glutamate produced a release of acetylcholine in the RVLM. Unilateral microinjection of L-glutamate into the pedunculopontine tegmental nucleus (PPT) also produced a pressor response, but the pressor response to L-glutamate was not affected by scopolamine injected ipsilaterally into the RVLM. These results provide evidence that the CG but not the PPT is involved in mediation of cholinergic inputs responsible for pressor responses in the RVLM.

Cholinergic neurons in numerous brain regions have been implicated in blood pressure regulation. One of the most important brain regions where cholinergic neurons play a role in the pathogenesis of hypertension is the rostral ventrolateral medulla (RVL), an essential source of efferent sympathetic activity. Pharmacological and biochemical studies have revealed that acetylcholine release in the RVL is increased in experimental hypertension regardless of its etiology and that this enhanced release of acetylcholine leads to hypertension. The lateral parabrachial nucleus, another important hindbrain area involved in blood pressure regulation, is responsible for the enhanced release of acetylcholine in the RVL of hypertensive animals. Moreover, recent studies have demonstrated the involvement of the hypothalamic defence area, an area believed to be involved in the hypertension induced by chronic stress, in the release of acetylcholine in the RVL and also have demonstrated the existence of direct projections from the hypothalamic structures to the lateral parabrachial nucleus. More studies about mechanisms of the enhanced release of acetylcholine in the RVL of experimentally hypertensive animals will provide important information for central mechanisms of hypertension.

We measured the activity of mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, in rat aortic strips with or without endothelium, and examined effects of angiotensin receptor antagonists, endothelin receptor antagonists and nitric oxide (NO)-related agents. Endothelium removal produced an activation of MAP kinase activity in the strips, whereas the enzyme activity was not affected in the adventitia. The MAP kinase activation was inhibited by either the angiotensin AT1 receptor antagonist losartan or the endothelin ETA receptor antagonist BQ 123. The combination of both antagonists caused an additive inhibition. The angiotensin AT2 receptor antagonist PD 123,319 and the endothelin ETB receptor antagonist BQ 788 did not affect the MAP kinase activation. The NO synthase inhibitor NG-nitro- l -arginine methyl ester ( l -NAME) caused an activation of MAP kinase in the endothelium-intact aorta and the MAP kinase activation was inhibited by losartan or BQ123. The NO releaser nitroprusside inhibited the MAP kinase activation induced by endothelium removal or angiotensin II. These results suggest that even in isolated arteries, NO of endothelial origin tonically exert MAP kinase-inhibiting effects and endogenous angiotensin II and endothelins in the media are tonically released to cause MAP kinase-stimulating effects in medial smooth muscle.

Studies using the whole-cell voltage-clamp technique have demonstrated that L-type Ca2+ channel activity is increased in vascular smooth. muscle cells from spontaneously hypertensive rats (SHR). We recorded L-type Ca2+ channel currents in cultured mesenteric artery smooth muscle cells from SHR and Wistar Kyoto (WKY) rats by using the cell-attached patch-clamp technique. Depolarizing voltage steps from a holding potential of -40mV elicited voltage-dependent inward Ba2+ currents. There was no difference in the L-type Ca2+ channel I-V curve or in the open probability between SHR and WKY. The inward currents were inhibited by the Ca2+ antagonists nifedipine and verapamil, but were enhanced by the Ca2+ agonist Bay K 8644 in a concentration-dependent manner. The Bay K 8644-induced increase and the nifedipine-induced inhibition of the inward currents were enhanced in SHR, whereas there was no difference in the verapamil-induced inhibition of the currents between the two strains of rats. These results suggest that the enhanced L-type Ca2+ channel activity observed in vascular smooth muscle cells from SHR is not due to altered function of a single L-type Ca2+ channel. It appears that the sensitivity of dihydropyridine receptors in the channels is enhan ced in SHR. (Hypertens Res 1998; 21: 33-37)

This study examines the effects of protein kinase inhibitors and activator on angiotensin II-induced DNA synthesis and protein synthesis of rat aortic smooth muscle cells. In quiescent confluent cells, angiotensin II induced a concentration-dependent increase in thymidine incorporation and leucine incorporation. The tyrosine kinase inhibitor genistein caused an inhibition of the angiotensin II-induced DNA synthesis but not of the agent-induced protein synthesis. The protein kinase C inhibitors staurosporine and calphostin C caused an inhibition of the angiotensin II-induced protein synthesis but not of the agent-induced DNA synthesis. The protein kinase C activator phorbol 12-myristate 13-acetate stimulated protein synthesis. Angiotensin II stimulated mitogen-activated protein (MAP) kinases and the angiotensin II-induced MAP kinase activation was inhibited by genistein but not by staurosporine. These findings suggest that angiotensin II-induced DNA synthesis is at least partly mediated via protein-tyrosine phosphorylation and angiotensin II-induced protein synthesis is at least partly mediated by activation of protein kinase C. It seems likely that MAP kinase activation is involved in DNA synthesis but not in protein synthesis induced by angiotensin II.

We examined whether baroreceptor activation causes a release of acetylcholine (ACh) in the rostral ventrolateral medulla (RVLM) of the rat, in order to investigate a possible connection between RVLM cholinergic systems and cardiovascular baroreflexes. Male Wistar rats were anesthetized, paralyzed and artificially ventilated. Either electrical stimulation of aortic nerve or baroreceptor activation by intravenous phenylephrine produced an increase of the release of ACh in the RVLM, whereas baroreceptor denervation and tetrodotoxin (TTX) microinfusion in the RVLM inhibited the increase in ACh release induced by phenylephrine. TTX injected in the caudal ventrolateral medulla (CVLM) inhibited the phenylephrine-induced increase of ACh release. The excitatory amino acid L-glutamate microinfused in the CVLM produced an release in ACh release in the RVLM. These results suggest that there is a connection between RVLM cholinergic systems and cardiovascular baroreflexes. It is probable that neurons in the CVLM are involved in mediating the release of ACh in the RVLM.

2-Amino-5-phosphonovalerate (AP5; 153 pmol) injected into the rostral ventrolateral medulla (RVLM) inhibited pressor responses induced by carotid chemoreceptor stimulation. AP5 also inhibited pressor responses to aspartate (0.75 nmol) but not to glutamate (0.53 nmol) similarly injected. High K+ (50 mM) released endogenous aspartate and glutamate in a Ca2+-dependent manner from the RVLM. Chemoreceptor stimulation caused a release of aspartate but not of glutamate in the RVLM, and sinus nerve denervation abolished the release of aspartate. Increases in blood pressure induced by intravenous phenylephrine did not release aspartate. These results support the hypothesis that endogenous aspartate in the rat RVLM is involved in the mediation of chemoreceptor reflexes.

In urethane-anesthetized rats with spinal transection, antagonists of excitatory amino acid receptors, P2 purinoceptors and adrenoceptors were microinjected into the paraventricular hypothalamic nucleus (PVN) and their effects on the pressor response evoked by carotid body chemoreceptor stimulation were examined. Microinjections of the non-selective excitatory amino acid antagonist kynurenate, the non-NMDA receptor antagonist CNQX and the NMDA antagonist 2-amino-5-phosphonovalerate (AP5) into the PVN inhibited the chemoreceptor reflex-induced pressor response. The excitatory amino acid agonist L-glutamate injected into the PVN produced an increase in blood pressure. The P2 purinoceptor antagonist suramin did not affect the pressor response and ATP did not affect basal blood pressure. The alpha adrenoceptor antagonist phentolamine, prazosin and yohimbine also inhibited the chemoreceptor-induced pressor response, while the beta antagonist propranolol did not affect it. These findings indicate that excitatory amino acid receptors and alpha adrenoceptors in the PVN are involved in mediating the pressor response induced by carotid body chemoreceptor stimulation in rats.

We examined whether reticulospinal sympathoexcitatory neurons in the rostral ventrolateral medulla (RVLM) have muscarinic receptors and ACh inputs, and whether these cholinergic mechanisms on RVLM neurons are involved in the pressor response induced by peripheral administration of physostigmine. Microiontophoretic application of ACh and carbachol enhanced the firing rate of RVLM sympathoexcitatory neurons and the enhancement of RVLM neurons by these cholinoceptor agonists was abolished by the nonselective muscarinic receptor antagonist scopolamine and/or by the M2 muscarinic receptor antagonist methoctramine. Physostigmine and the ACh releaser 3,4-diaminopyridine also enhanced the firing rate of RVLM neurons. Intravenous administration of physostigmine enhanced RVLM sympathoexcitatory neuronal activity and the physostigmine-induced response was reversed by iontophoretic application of scopolamine onto the neurons. These results are consistent with the hypothesis that M2 muscarinic receptors responsible for blood pressure regulation are present on RVLM sympathoexcitatory neurons and these receptors receive ACh inputs. Physostigmine injected systemically may exert a portion of its hypertensive effect through a direct enhancement of cholinergic mechanisms on RVLM sympathoexcitatory neurons.

1. The effects of electrical stimulation and microinjection of morphine into the periaqueductal gray (PAG) on the 5-hydroxyindole oxidation current (280-300 mV) in laminae I-VI (800-2500 microns) of the spinal cord were examined using in vivo voltammetry in anesthetized cats. 2. Electrical stimulation of the PAG (PAG-S) both enhanced and attenuated the current. PAG-S increased the signal by 13.3 +/- 3.7% (laminae I-II: 800-1200 microns) or 19.0 +/- 3.6% (laminae V-VI: 1700-2500 microns) in comparison to control values. Attenuation by PAG-S decreased the signal by 15.3 +/- 2.6% (laminae I-II) or 13.3 +/- 2.0% (laminae V-VI) of control values. Naloxone antagonized signal enhancement by PAG-S. 3. Morphine (10 micrograms/microliter) microinjected into the PAG significantly increased the height of the signal (laminae I-II: 15.0 +/- 3.4%, laminae V-VI: 12.2 +/- 1.5%). Enhancement by microinjected morphine was antagonized by naloxone. In contrast, microinjected morphine also significantly decreased the signal by 10.4 +/- 2.7% (laminae I-II) and by 10.3 +/- 1.3% (laminae V-VI) of control values. 4. Microinjection of morphine and electrical stimulation of the PAG was observed both to enhance and attenuate the oxidation current of 5-hydroxyindole in the superficial and deeper dorsal horn. PAG may function to regulate the RVM-spinal serotonergic pathway, which modulates the transmission of nociceptive messages at the spinal cord.

A conditioned stimulus previously paired with electric footshock produced an increase in blood pressure in conscious, freely moving rats. The conditioned pressor response was reproducible. Intracerebroventricular injection of the nicotinic receptor antagonists hexamethonium (1-10 micrograms) or pentolinium (10 micrograms) but not the muscarinic receptor antagonist methylatropine (3 micrograms) produced an inhibition of the conditioned pressor response, whereas intraarterial injection of hexamethonium (10 micrograms) did not affect the response. Intraventricular injection of the cholinesterase inhibitor physostigmine (3-10 micrograms) produced an enhancement of the conditioned pressor response. These results are consistent with the possibility that central nicotinic receptors play a role in the expression of the emotionally conditioned pressor response in rats.

湿熱処理 (121℃, 15分) を施した干しシイタケとフラクトオリゴ糖の7: 3からなる混合物 (SK-204) が高血圧ラットに及ぼす作用について検討し, つぎの結果を得た。1) SHRに10%SK-204混合飼料を与えた群では, 14日以降に血圧上昇抑制および50日後における心臓の体重当り相対重量が対照群に対して有意に減少した。また, 脳および腎臓の病理組織学検査結果, 脳について基質的な変化は減弱する傾向を示した。2) Dahl Sを2群に分け, 1群は対照群として8%食塩混合飼料と, 他の1群にはこれに10%の割合でSK-204を混合した飼料で飼育した。28日後の収縮期血圧に有意の差が認められた。31日以降, 対照群に体重, 血圧の低下, 自発運動の抑制, 運動障害, 前後肢の麻痺発生等がおこり, 脳内出血がみられた。SK-204を併食すると, これらの症状がみられず, 心臓重量も対照群に比べ有意に減少した。また, 腎臓の病理組織学的検査による基質的障害も減弱する傾向を示した。以上, SK-204は血圧上昇抑制作用に加え, 心肥大および脳出血の発症を抑制する作用をもつことが示唆された。

We examined whether the selective 5-hydroxytryptamine 1A (5-HT1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) injected systemically can act directly on sympathoexcitatory neurons located in the rostral ventrolateral medulla (RVLM) to cause the hypotensive effect of this agent in rats. Microinjections of 8-OH-DPAT and buspirone into the RVLM produced a dose-dependent decrease in blood pressure. Microinjections of spiperone and pindolol, 5-HT1A antagonists, into the RVLM inhibited the depressor response to 8-OH-DPAT intravenously injected or injected into the RVLM. Microiontophoretic application of 8-OH-DPAT onto RVLM sympathoexcitatory neurons inhibited the firing of RVLM sympathoexcitatory neurons and the inhibition of unit activity by 8-OH-DPAT was blocked by microiontophoretic spiperone. Intravenous administration of 8-OH-DPAT also inhibited the firing of these neurons. Microiontophoretic application of spiperone onto the RVLM sympathoexcitatory neurons reversed the inhibitory response to intravenous 8-OH-DPAT. These results are consistent with the hypothesis that 8-OH-DPAT may exert a portion of its hypotensive effect through a direct inhibition of RVLM sympathoexcitatory neurons in rats. The receptor involved is probably the 5-HT1A type.

In urethane-anesthetized rats, excitatory amino acid antagonists were microinjected into the rostral ventrolateral medulla (RVLM) and their effects on the pressor response and tachycardia evoked by carotid chemoreceptor stimulation were examined. Microinjections of the N-methyl-D-aspartate (NMDA) receptor antagonists 2-amino-5-phosphonovalerate (AP5) and MK-801 into the RVLM inhibited these chemoreceptor reflex responses whereas these responses were not affected by injection of the non-NMDA receptor antagonist CNQX. AP5 and MK-801 but not CNQX abolished the pressor response evoked by NMDA whereas CNQX but not AP5 and MK-801 abolished that evoked by AMPA or kainate. These results provide evidence that NMDA receptors in the RVLM of the rat are involved in the carotid chemoreceptor reflex.

1. 1. Using in vivo microdialysis, we studied the effects of apomorphine on the release of acetylcholine (ACh) in the striatum of freely-moving rats. 2. 2. Basal release of ACh was 3.01 ± 0.51 pmol/15 min in 30 μl (containing of 10 μM neostigmine) of the striatal perfusate. 3. 3. Ringer containing tetrodotoxin (1 μM), hemicholinium-3 (5 mM), or Ca2+-free Ringer was perfused into the striatum. Each of these treatments produced a significant attenuation in release content of ACh. High K+ (30 mM) produced a significant increase in ACh release. 4. 4. In normal rats, apomorphine (0.05 mg/kg, s.c.) increased striatal ACh release. A high dose (1.0 mg/kg) significantly attenuated release. 5. 5. In 6-OHDA-pretreated rats, although the lower dose of apomorphine did not increase striatal ACh release, the high dose produced a more significant attenuation of release. 6. 6. It is concluded that apomorphine enhanced or attenuated the striatal ACh release and that this effect was regulated by nigro-striatal dopaminergic system in the freely moving rats.

Unilateral microinjections of GABA, glycine, beta-alanine and taurine into the caudal ventrolateral medulla (CVLM) of the rat, led to an increase in blood pressure and heart rate. The responses to glycine, beta-alanine and taurine but not to GABA could be blocked by strychnine. The responses to taurine and beta-alanine but not to GABA and glycine could be blocked by 6-aminomethyl-3-methyl-4H-1,2,4-benzothiadiazine-1,1-dioxide (TAG), an antagonist of taurine. The taurine antagonist alone injected bilaterally into the CVLM produced a decrease in blood pressure. From CVLM areas microperfused with Krebs solution, spontaneous release of GABA, glycine, beta-alanine and taurine was detected and high K+ stimulation caused a calcium-dependent release of GABA, beta-alanine and taurine. These results suggest that beta-alanine and taurine as well as GABA may be involved in modulation of the cardiovascular control within the CVLM.

Microinjections of L-DOPA (10-100 ng) into the medial area of the nucleus tractus solitarii (NTS) led to dose-dependent decreases in arterial blood pressure and heart rate in rats treated with i.p. 3-hydroxybenzylhydrazine, a central inhibitor of DOPA decarboxylase, or similarly with intraventricular 6-hydroxydopamine. D-DOPA, dopamine or noradrenaline (100 ng) produced no effect. L-DOPA methyl ester (1 microgram), a competitive antagonist for L-DOPA, microinjected into NTS, blocked the depressor and bradycardic responses to L-DOPA. High K+ (40 mM) released endogenous DOPA in a Ca(2+)-dependent manner from slices of the rat dorsomedial medulla including NTS. These results support the hypothesis that there exist systems of L-DOPA itself responsible for cardiovascular regulation in NTS of rats. This regulatory action of L-DOPA seems to be postsynaptic in nature.

Microinjections of α-methylnoradrenaline and tyramine into the rat nucleus tractus solitarii (NTS) potentiated the depressor and bradycardic responses to aortic nerve stimulation whereas yohimbine injected similarly inhibited them. NTS pretreatment with yohimbine inhibited the baroreflex potentiation effects of α-methylnoradrenaline and tyramine whereas intraventricular pretreatment with 6-hydroxydopamine inhibited only that of tyramine. These results provide evidence that endogenous catecholamines in the rat NTS are involved in alpha2 adrenoceptor-mediated modulation of the aortic baroreceptor reflex.

Neuropeptide Y (NPY), neurotensin, arginine vasopressin (AVP), angiotensin II (ANG II), atrial natriuretic peptide (ANP) and calcitonin gene-related peptide (CGRP) have been suggested as putative neurotransmitters in the nucleus tractus solitarii (NTS) where baro- and chemoreceptor afferents terminate. To investigate modulation of the aortic baroreceptor reflex by neuropeptides, we microinjected these neuropeptides into the medial area of the rat NTS and examined their effects on the depressor and bradycardic responses to electrical stimulation of the aortic nerve which contains mainly baroreceptor afferent fibers in rats. Male Wistar rats were anesthetized with urethane, paralyzed and artificially ventilated. NPY (3 ng) and neurotensin (0.3 ng) injected into the NTS caused a decrease in blood pressure and/or heart rate, and facilitated the depressor and bradycardic responses to aortic nerve stimulation. AVP (3 ng) produced an increase in blood pressure and heart rate, and inhibited the responses to aortic nerve stimulation, whereas d(CH2)5Tyr(Me)AVP(100 ng), a V1 vasopressin receptor antagonist, did not affect the basal cardiovascular parameters and the baroreflex responses. ANG II (0.3 and 3 ng) caused a decrease in blood pressure and heart rate whereas at 0.3 ng it did not affect the baroreflex responses. ANP (3 ng) and CGRP (3 ng) did not affect the basal blood pressure and heart rate, and the responses to aortic nerve stimulation. These findings indicate that NPY, neurotensin and AVP microinjected into the rats NTS can modify the aortic baroreceptor reflex. Some of these neuropeptides may play a role in modulation of the aortic baroreceptor reflex within the NTS.

Concentrations of gamma-aminobutyric acid (GABA) and other amino acids were measured in microdissected areas of the rostral ventro-lateral medulla (RVL), nucleus tractus solitarii (NTS) and caudal ventrolateral medulla (CVL) of the rat, and effects on the amino acid levels, of hypotension induced by hexamethonium and nifedipine were examined. Hexamethonium and nifedipine decreased concentrations of GABA in all the regions studied, while concentrations of glycine, beta-alanine and taurine were not affected by these agents. Both agents caused a prolonged fall in blood pressure. These results strongly suggest that a decrease in blood pressure produces a decrease in GABA levels in the brainstem regions of the rat.

Microinjections of beta-alanine and glycine into the nucleus tractus solitarii (NTS) of the rat, led to an increase in blood pressure and heart rate. The responses to glycine but not to beta-alanine could be blocked by strychnine. Both amino acids reduced the responses to aortic nerve stimulation. High K+ stimulation caused a calcium-dependent release of beta-alanine from tissues in the area of the NTS. These results suggest that beta-alanine and glycine may modulate the cardiovascular control within the NTS.

Previously, we have demonstrated that intravenous phenylephrine-induced increases in blood pressure inhibit angiotensin II-sensitive neurons via gamma-aminobutyric acid (GABA) inputs in the anterior hypothalamic area (AHA). The lateral septal area (LSV) is also demonstrated to be involved in mediation of the baroreceptor reflex. To investigate central mechanisms involved in mediating the baroreceptor reflex, we examined whether GABA in the LSV is involved in mediation of the phenylephrine-induced inhibition of AHA angiotensin II-sensitive neurons. Microinjection of GABA into the LSV inhibited angiotensin II-sensitive neurons in the AHA of rats. The LSV GABA-induced inhibition of AHA neurons was abolished by pressure application of bicuculline onto the same AHA neurons. Intravenous injection of phenylephrine also inhibited AHA angiotensin II-sensitive neurons and the phenylephrine-induced inhibition of AHA neurons was abolished by microinjection of the GABAA receptor antagonist bicuculline into the LSV. In contrast, the LSV microinjection of bicuculline did not affect the inhibition of firing of AHA neurons induced by GABA pressure-applied in the AHA. These findings suggest that intravenous phenylephrine inhibits AHA angiotensin II-sensitive neurons via release of GABA in the LSV.

This article reviews studies by the author on central mechanisms of hypertension. Spontaneously hypertensive rats (SHR) have been developed as a rat model of genetic hypertension, and central acetylcholine has been implicated in hypertension in SHR. The rostral ventrolateral medulla (RVL), a major source of efferent sympathetic activity, has cholinergic pressor systems. The release of acetylcholine is enhanced in the RVL of SHR, leading to hypertension. The alteration of the RVL cholinergic system in SHR results from enhanced angiotensin systems in the anterior hypothalamic area (AHA). Angiotensin II-sensitive neurons are present in the AHA and they are tonically activated by endogenous angiotensins. The basal activity of AHA angiotensin II-sensitive neurons is enhanced in SHR, mainly due to enhanced sensitivity of AHA neurons to angiotensin II. The AHA angiotensin system is also responsible for hypertension induced by emotional stress and central Na(+) increases. These findings suggest that the AHA angiotensin system may play a critical role in the development of hypertension.

Previously, we have demonstrated that pressure-ejected application of angiotensin II onto some neurons in the anterior hypothalamic area (AHA) of rats increases their firing rate. In contrast, pressure application of the angiotensin AT1 receptor antagonist losartan onto AHA neurons blocked the basal firing of the neurons. To investigate possible participation of these AHA neurons in the brain angiotensin system, we examined whether intracerebroventricular injection of angiotensin II results in an activation of angiotensin II-sensitive neurons in the AHA of rats. Intracerebroventricular injection of angiotensin II increased the firing rate of AHA angiotensin II-sensitive neurons. The angiotensin II-induced increase of unit firing in AHA neurons was abolished by pressure application of losartan onto the same neurons. In addition, the angiotensin II-induced increase of firing in AHA neurons was abolished by pressure application of N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W7), a calmodulin inhibitor, onto the same neurons. Pressure application of W7 onto AHA neurons affected neither the basal firing rate nor the increase in unit firing induced by pressure application of angiotensin II onto the same neurons. Intracerebroventricular injection of the cholinergic agonist carbachol did not affect the firing rate of angiotensin II-sensitive neurons in the AHA. These findings suggest that intracerebroventricular injection of angiotensin II activates AHA angiotensin II-sensitive neurons via angiotensinergic inputs to the neurons.

Previously, we have demonstrated that angiotensin II-sensitive neurons exist in the anterior hypothalamic area (AHA) and that these neurons are tonically activated by endogenous angiotensins in rats. Chemical stimulation of the lateral septal area (LSV) and medial amygdaloid nucleus (MeA), and intracerebroventricular injection of hypertonic saline, activated AHA angiotensin II-sensitive neurons. To investigate mechanisms of the basal activity of AHA angiotensin II-sensitive neurons, we examined the effect of N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W7), a calmodulin inhibitor, applied onto AHA neurons on the basal activity and the stimulus-evoked activation of these neurons. Male Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Microinjections of carbachol into the LSV and corticotropin-releasing factor into the MeA, and intracerebroventricular injection of hypertonic saline, activated AHA angiotensin II-sensitive neurons. These three kinds of injection-induced activations of AHA neurons were abolished by pressure application of W7 onto the same neurons, while the calmodulin inhibitor did not affect the increase in firing of AHA neurons induced by pressure application of angiotensin II onto the same neurons. The pressure application of W7 did not affect the basal activity of AHA angiotensin II-sensitive neurons, whereas the angiotensin AT1 receptor antagonist losartan similarly applied inhibited it. These findings suggest that the basal activity of AHA angiotensin II-sensitive neurons is mediated by angiotensins released not via synaptic inputs.

It has been suggested that intracerebroventricular injection of hypertonic saline mimics the effects of a high salt diet in spontaneously hypertensive rats (SHR), a genetic model of hypertension. Intracerebroventricular injection of hypertonic saline produces an increase in blood pressure and the pressor response to hypertonic saline is enhanced in adult hypertensive SHR. In this study, we examined whether the intracerebroventricular hypertonic saline-induced pressor response is enhanced even in pre-hypertensive SHR. The basal mean blood pressure was almost the same in 4-week-old SHR and age-matched Wistar Kyoto rats (WKY), whereas it was greater in 15–16-week-old SHR than in age-matched WKY. Intracerebroventricular injection of hypertonic saline (10 μl of 230 mM NaCl) produced an increase in blood pressure in both 4-week-old and 15–16-week-old SHR, whereas it did not affect blood pressure in both age-matched WKY. Intracerebroventricular injection of hypertonic saline (10 μl of 260 mM NaCl) produced an increase in blood pressure in all rats but the pressor response was greater in both 4-week-old and 15–16-week-old SHR than in respective age-matched WKY. Intracerebroventricular injection of Phe-Met-Arg-Phe amide (FMRF), an FMRF-inducible sodium channel activator, produced an increase in blood pressure in all rats but the pressor response was greater in SHR than in WKY at both ages. These findings indicate that the sensitivities of pressor responses to intracerebroventricular hypertonic saline and FMRF are enhanced not only in hypertensive but also in pre-hypertensive SHR.