Role of nitric oxide and acetylcholine in neocortical hyperemia elicited by basal forebrain stimulation: evidence for an involvement of endothelial nitric oxide

We examined the role of acetylcholine and nitric oxide in the increases in cerebrocortical blood flow elicited by stimulation of a region of the basal forebrain from which the major cholinergic projection to the cerebral cortex originates. In halothane-anesthetized rats a 3 x 3 mm area of the parietal cortex was exposed and the site was superfused with Ringer (37 degrees C; pH 7.3-7). Cortical blood flow was monitored at the site of superfusion by laser-Doppler flowmetry. The basal forebrain was stimulated electrically (100 microA; 50 Hz) and stimulated sites were histologically verified at the end of the experiment. With Ringer superfusion (n = 8), basal forebrain stimulation increased neocortical flow by 185 +/- 9% (mean +/- S.E.M.). The flow increase was attenuated (-38 +/- 6%; n = 5) by superfusion with the muscarinic cholinergic antagonist atropine (100 microM). Superfusion with atropine plus the nicotinic antagonist mecamylamine (100 microM) did not attenuate the response further (P > 0.05 from atropine alone; n = 6). Superfusion with the nitric oxide synthase inhibitor nitro-L-arginine, but not with the inactive isomer nitro-D-arginine (n = 6), attenuated the vasodilation in a dose-dependent fashion (-43 +/- 4% at 1 mM; n = 7) and reduced nitric oxide synthase catalytic activity at the site of superfusion by 95 +/- 4%. Co-application of nitro-L-arginine and atropine did not attenuate the vasodilation further (P > 0.05 from nitro-L-arginine alone; n = 6). Administration of the somewhat selective inhibitor of neuronal nitric oxide synthase 7-nitroindazole (50 mg/kg, i.p.) attenuated the increases in flow produced by topical application of N-methyl-D-aspartate (40 microM; n = 5) or by hypercapnia (n = 7), but did not affect the vasodilation produced by basal forebrain stimulation (n = 5) and by topical application of acetylcholine (10 microM; n = 5). 7-nitroindazole reduced constitutive nitric oxide synthase enzymatic activity in forebrain by 72 +/- 3% (n = 8). The data suggest that the neocortical vasodilation elicited by basal forebrain stimulation is, in part, mediated by local release of acetylcholine which, in turn, leads to increased nitric oxide synthesis in endothelial cells.     

Hypercapnic cerebral blood flow in spontaneously hypertensive rats

OBJECTIVE: Hypercapnic cerebral vasodilation appears to be endothelium-dependent, as it involves nitric oxide and prostaglandins. Since chronic hypertension has been associated with impaired endothelial function, we designed a study to find out whether hypercapnic cerebral blood flow and its nitric oxide- and prostaglandin-sensitive component is reduced in spontaneously hypertensive rats (SHR) compared with normotensive controls. METHODS: Cerebral blood flow was measured in enflurane-anesthetized SHR (n=53), Wistar-Kyoto (WKY, n=20) and Sprague-Dawley (n=50) rats using the hydrogen clearance method. Cerebral blood flow was measured during eucapnia and hypercapnia; it was also assessed after administering either nonisoform-selective or isoform-selective neuronal nitric oxide synthase inhibitors and during inhibition of prostaglandin production. RESULTS: Hypercapnic cerebral blood flow did not differ among the strains. Nitric oxide synthase inhibition with intracortical N(G)-monomethyl-L-arginine reduced hypercapnic cerebral blood flow in SHR by 23+/-4% and in Sprague-Dawley rats by 23+/-7% without affecting eucapnic flow. Intraperitoneal administration of the inhibitor of neuronal nitric oxide synthase, 7-nitroindazole, reduced eucapnic flow by 18+/-5% in SHR and 27+/-5% in WKY rats, and hypercapnic flow by 48+/-3 and by 51+/-6%, respectively. Indomethacin produced a similar decrease in hypercapnic flow in Sprague-Dawley rats and SHR (49+/-5 and 62+/-4%, respectively). CONCLUSION: Hypercapnic cerebral blood flow was not impaired in SHR. The contribution of nitric oxide- and prostaglandin-dependent vasodilation appeared to be intact Our results are consistent with the hypothesis that neuronal rather than endothelial production of nitric oxide may be responsible for maintaining hypercapnic cerebral vasodilation in SHR.     

Carbon monoxide regulates cerebral blood flow in epileptic seizures but not in hypercapnia

Carbon monoxide (CO) is an endogenously produced gas sharing many properties with nitric oxide (NO), notably activating soluble guanylate cyclase and relaxing blood vessels. The brain can generate high quantities of CO from a constitutive enzyme, haem oxygenase (HO-2). To determine whether CO is involved in the regulatory mechanisms of cerebral blood flow (CBF), two conditions associated with a reproducible CBF increase were studied in rats: epileptic seizures induced by kainate, and hypercapnia. The HO inhibitor tin protoporphyrin (Sn-PP) did not modify the basal level of CBF, significantly reduced the increase in CBF during status epilepticus, and did not affect the cerebrovascular response to hypercapnia. It is concluded that CO participates in the regulation of CBF in specific conditions, notably those associated with glutamate release.     

Role of nitric oxide in maintenance of basal anterior choroidal blood flow in rats

PURPOSE: The aim of this study was to use laser Doppler flowmetry to measure anterior choroidal blood flow in the anesthetized rat and to determine the role of nitric oxide (NO) in the maintenance of basal ocular blood flow in vivo. METHODS: By using laser Doppler flowmetry, blood flow from the anterior choroid in pentobarbital-anesthetized rats was measured continuously. Graded single doses (0.03-300 mg/kg) of the nonselective NO synthase inhibitor NG-nitro-L-arginine-methyl ester (L-NAME) were administered intravenously to establish dose-response relationships. Other groups of animals were tested with L-NAME after the prior administration of L-arginine, with D-NAME, or with the selective neural NO synthase inhibitor 7-nitroindazole. RESULTS: Intravenous administration of L-NAME produced a dose-related depression of anterior choroidal blood flow in the 0.3- to 30-mg/kg range. Maximal depression of approximately 60% occurred at the 30-mg/kg dose, peaked at approximately 30 minutes, and lasted throughout the 60-minute experimental period. At 10 mg/kg, L-NAME reduced ocular blood flow by approximately 50%, an effect that was abolished by pretreatment with intravenous L-arginine (300 mg/kg). Both D-NAME (10 mg/kg, intravenously) and 7-nitroindazole (50 mg/kg, intraperitoneally) were inactive with regard to ocular blood flow depression. CONCLUSIONS: Laser Doppler flowmetry appears to be a useful tool for continuous, online measurement of anterior choroidal blood flow in the rat eye. Results with L-NAME and 7-nitroindazole suggest that local tonic generation of endothelial NO plays an important role in the maintenance of basal anterior choroidal blood flow in this species.     

Nitric oxide signalling is required for the generation of anoxia-induced long-term potentiation in the hippocampus

The involvement of nitric oxide in anoxia-induced long-term potentiation (anoxic LTP) of synaptic transmission was investigated in CA1 neurons of rat hippocampal slices using intracellular recording techniques in vitro. In response to superfusion of an anoxic artificial cerebral spinal fluid saturated with 95% N2-5% CO2, the excitatory postsynaptic potential (EPSP) generated in hippocampal CA1 neurons by stimulation of the Schaffer collateral/commissural afferent pathway was completely abolished within 10 min of anoxia. On return to reoxygenated medium, the EPSP returned to the control value within 10 min and was subsequently and progressively potentiated to reach a plateau 15-20 min after return to oxygen. This anoxia-induced persistent increase in synaptic transmission lasted for more than 1 h. Application of the nitric oxide synthase inhibitors 7-nitroindazole (7-NI) or L-N(G)-nitroarginine (NOARG) produced no effects on the baseline EPSP amplitude, but effectively attenuated the anoxic LTP. The inhibitory effects of both 7-NI and NOARG on the anoxic LTP were blocked by L-arginine, a substrate for nitric oxide synthase. These results suggest that nitric oxide is required for the generation of anoxia-induced LTP of glutamatergic synaptic transmission in the CA1 region of the rat hippocampus.     

Measurement of nitric oxide in the rat cerebral cortex during hypercapnoea

Changes in nitric oxide (NO) concentration and cerebral blood flow (CBF) in the parietal cortex during hypercapnoea were investigated in anaesthetized rats, using a NO-selective electrode and laser Doppler flowmetry. When hypercapnoea was induced by inhalation of 5% CO2 for 10 min, both the NO concentration and CBF increased. After administration of 7-nitroindazole, a neuronal NO synthase (nNOS) inhibitor, both the basal NO and CBF decreased, and responses to hypercapnoea were also significantly suppressed by 70.1% and 73.2%, respectively, compared with the control state. These results suggest that NO derived from nNOS is involved not only in maintaining resting cerebral circulation but also in regulating CBF response during hypercapnoea.     

Effects of 7-nitroindazole, NG-nitro-L-arginine, and D-CPPene on harmaline-induced postural tremor, N-methyl-D-aspartate-induced seizures, and lisuride-induced rotations in rats with nigral 6-hydroxydopamine lesions

The present behavioral study was undertaken to investigate whether neuronal nitric oxide (NO) synthase mediates the abnormal consequences of increased NMDA receptor-mediated synaptic transmission in models of postural tremor, Parkinson's disease and epilepsy. We used 7-nitroindazole, a selective inhibitor of neuronal NO synthase, and NG-nitro-L-arginine (L-NAME), an unspecific NO synthase inhibitor, and compared their action with that of the competitive NMDA receptor antagonist 3-[(R)-2-carboxypiperazin-4-yl]-prop-2-enyl-1-phosphonic acid (D-CPPene). In both mice and rats, 7-nitroindazole, L-NAME and D-CPPene dose dependently reversed the harmaline-induced increase of cerebellar cyclic guanosine-5'-monophosphate (cGMP) levels. For subsequent behavioral experiments we used doses of 7-nitroindazole, L-NAME and D-CPPene which were equipotent in preventing harmaline-induced cGMP increase. Harmaline-induced tremor in mice and rats was suppressed by D-CPPene, but not by 7-nitroindazole or by L-NAME. This effect of D-CPPene was not due to unspecific suppression of motor activity, since D-CPPene did not affect locomotor activity at doses which reduced tremor. D-CPPene, but not 7-nitroindazole and L-NAME potentiated the antiparkinsonian action of the dopamine agonist lisuride in rats with unilateral 6-hydroxydopamine lesions of the substantia nigra. D-CPPene antagonized seizures induced by intracerebroventricular injection of NMDA in mice. In contrast, 7-nitroindazole and L-NAME had only a tendency to prevent seizures and to delay the latency to onset of seizures. We conclude from these results that neuronal NO synthase does not serve as a major mediator of increased NMDA receptor-mediated synaptic transmission in animal models of Parkinson's disease, postural tremor and epilepsy. The novel observation that D-CPPene suppresses harmaline-induced tremor leads us to suggest that NMDA receptor antagonists should be considered as novel therapeutics for postural tremor.     

Possible role for nitric oxide releasing nerves in the regulation of ocular blood flow in the rat

AIM: To investigate the role of nitrergic nerves in the regulation of ocular blood flow. METHODS: Conscious, lightly restrained rats were treated with either the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI), or the nonselective inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), and ocular blood flow was measured ex vivo from tissue samples, using the fully quantitative [14C]-iodoantipyrine technique. RESULTS: In the peripheral circulation, L-NAME produced an increase in arterial blood pressure (+22%) while 7-NI had no effect. In contrast, both 7-NI and L-NAME produced significant decreases in ocular blood flow (-31% and -59% respectively). The ocular vascular resistance calculated from ocular blood flow and mean arterial blood pressure increased by 29% following 7-NI, but by 130% following L-NAME. CONCLUSIONS: Nitric oxide releasing neurons may play an important contributory role in regulating ocular blood flow.     

Neo-flaps for facial reconstruction: can we create the desired thin-skin flaps?

The involvement of the L-arginine-nitric oxide (NO) pathway in the pathogenesis of hyperoxia-induced seizures was studied by using agents controlling NO levels. We selected two inhibitors of nitric oxide synthase, the systemic inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) and the novel cerebral-specific inhibitor 7-nitroindazole, and two generators of NO, the NO donor S-nitroso-N-acetylpenicillamine and the physiological precursor L-arginine. Rats with chronic cortical electrodes were injected intraperitoneally with different doses of one of the agents or their vehicles before exposure to 0.5 MPa O2 and O2 with 5% CO2 at an absolute pressure of 0.5 MPa. The duration of the latent period until the onset of electrical discharges in the electroencephalogram was used as an index of central nervous system O2 toxicity. The two nitric oxide synthase inhibitors L-NAME and 7-nitroindazole significantly prolonged the latent period to the onset of seizures on exposure to both hyperbaric O2 and to the hypercapnic-hyperoxic mixture. Pretreatment with the NO donor S-nitroso-N-acetylpenicillamine significantly shortened the latent period, whereas L-arginine, the physiological precursor of NO, significantly prolonged the latent period to onset of seizures. Our results suggest that the L-arginine-NO pathway is involved in the pathophysiology of hyperoxia-induced seizures via various regulating mechanisms.     

NMDA antagonist displays anticonvulsant effect via NO synthesis inhibition in penicillin-treated rat hippocampal slices

The present study investigated the role of nitric oxide (NO) in epileptogenesis and whether this role correlated with ionotropic glutamate receptor (IGR). Using a self-constructed NO-sensitive microelectrode (SNM), we observed the effect of nitric oxide synthase (NOS) inhibitors, NMDA and non-NMDA selective antagonists on penicillin(PEN)-treated hippocampal slices by simultaneously recording evoked field potentials and nitric oxide release from CA1 pyramidal neurons. 7-nitroindazole (7-NI),Nomega-nitro-L-arginine (L-NNA) and DL-2-amino-phospho-novaleric acid (APV), but not 6,7-dinitroquinoxaline-2,3 (1h,4h)-dione(DNQX), depressed NO release and partly reversed PEN's epileptogenetic effect, while APV + 7-NI + L-NNA did not display a further inhibitory effect. These findings suggest both NOS inhibitor and NMDA antagonist involve as anticonvulsant factors in epileptogenesis, providing direct evidence for NO release in response to NMDA receptor activation. The anticonvulsant effect of NMDA antagonist may ascribe to its action on NO release.     

Action-potential duration and contractility in canine cardiac tissues: action of inotropic drugs

The goal of this study was to determine whether neuronally derived nitric oxide mediates responses of cerebral blood flow (CBF) to N-methyl-D-aspartate (NMDA). In anesthetized Sprague-Dawley rats, regional CBF of the parietal cortex was monitored by laser-Doppler flowmetry. Topical application of either NMDA or acetylcholine produced concentration-related increases in CBF. Responses of CBF to NMDA (10(-5) M) but not to acetylcholine were inhibited (0+/-3% vs 21+/-5%, p < 0.05) by 7-nitroindazole (50 mg/kg, i.p.). MK-801 (0.5 mg/kg, i.v.) and tetrodotoxin (10(-6) M, topical application) also inhibited NMDA-induced responses. These results suggest that nitric oxide of neuronal origin mediates NMDA-induced increases in CBF.     

Factors determining proconvulsant and anticonvulsant effects of inhibitors of nitric oxide synthase in rodents

Although a majority of studies suggest that inhibitors of nitric oxide synthase (NOS) are proconvulsant, a substantial minority indicate the opposite (i.e. that inhibitors of NOS are anticonvulsant). As a consequence, the role of endogenous nitric oxide (NO) in the expression of seizures is unclear. In the present series of experiments, we therefore assessed factors governing pro- and anticonvulsant effects of inhibitors of NOS. In mice receiving systemic injections of kainate or picrotoxin, we confirmed the hypothesis that the effects of inhibitors of NOS vary with the model of seizure: Whereas 7-nitroindazole (7-NI) reduced the latency and increased the severity of kainate-induced convulsions (Expt. 1), both 7-NI and N(omega)-nitro-L-arginine methyl ester (L-NAME) slightly delayed clonus following the systemic administration of picrotoxin at doses > or = 3.5 mg/kg but not at doses < or = 3.0 mg/kg (Expts. 2-5). Paradoxically, L-NAME but not 7-NI significantly reduced the CD50 of picrotoxin, which was approximately 2 mg/kg in control mice (Expt. 4), revealing inhibitor-specific interactions with the dose of the convulsant. Finally, we determined in rats that the effects of L-NAME on kainate-induced seizures vary as a function of genetic factors: L-NAME significantly potentiated kainate-induced convulsions in Sprague-Dawley rats but not in Wistar rats (Expt. 6).     

Status epilepticus in immature rats. Protective effects of glucose on survival and brain development

The role of glucose metabolism in alleviating the complications of status epilepticus (SE) was investigated in developing rats. Pretreatment with glucose reduced mortality from SE by 90% in rats under 1 week of age, 80% in 10-day-old rats, 50% in 15- to 20-day-olds, and not at all in adults. In 4-day-old animals, brain DNA synthesis during seizures, and in survivors, brain weight, DNA, RNA, protein, and cholesterol contents at 7 days of age were reduced less in glucose-treated than in saline-treated littermates. In the saline group, seizures caused a progressive fall in brain glucose level but no fall in blood glucose level, suggesting that glucose transport from blood to brain could not keep pace with glycolytic demands. In glucose-treated rats, blood and brain glucose concentrations remained elevated throughout the convulsive period. There was no reduction of brain adenosine triphosphate levels in either group. Thus, the protection by glucose appears to be related to its roles as a carbon source rather than an energy source. It is concluded that in immature animals, depletion of brain glucose can occur in the absence of hypoglycemia, and may be an important and potentially treatable complication of status epilepticus.     

Induction of astroglial gene expression by experimental seizures in the rat: spatio-temporal patterns of the early stages

The levels of glial fibrillary acidic protein mRNA were analysed by in situ hybridization during the first 6 h in experimental models of status epilepticus in the rat. Two different models of status epilepticus were studied: one is produced by the administration of pilocarpine to lithium-treated rats and the other by the intracerebroventricular administration of kainate. Results obtained in the present study showed a very rapid (as early as 1.5 h in periventricular zones of hypothalamus, cerebral cortex, and hippocampal area) up-regulation of GFAP mRNA levels following the pharmacological induction of seizures. Several other areas showed a GFAP activation starting at 3 h such as septum, habenular nuclei, corpus callosum, and cingulum. The comparison of the results obtained in the two models of status epilepticus revealed interesting differences in some brain areas, such as cerebellum and striatum, which can be related to the specific neurotransmitter receptors and neurochemical pathways stimulated by the drugs. Interestingly, some brain areas whose neurons are strongly activated by pilocarpine and kainate (amygdala and CA3 hippocampal field) and that undergo neuronal degeneration did not show the early GFAP response. An interesting spatial feature was observed in several brain regions examined (striatum, septum, and hypothalamus): the response first appeared in the periventricular zones and then diffused to the rest of the brain area. In general GFAP responses in the periventricular zones were early and intense.     

The effects of kainic acid in rats with spontaneous recurrent seizures

1. Rats with spontaneous recurrent seizures (SRS) were obtained by injection of kainic acid (KA; 10 mg/kg SC) to drug-naive rats that regularly developed wet-dog shakes followed by complex partial seizures and status epilepticus. Three to five weeks later, the rats with manifest SRS were selected. 2. The SRS rats were challenged with KA (10 mg/kg SC). The seizures induced in SRS rats by KA were similar to SRS regarding their clinical stage and duration (mean duration of seizures: 44 sec and 43 sec, respectively). The frequency of seizures was, however, increased compared with the frequency of SRS in control, vehicle-treated SRS rats (mean frequency of seizures: 12.9 and 0.4 per 3 hr, respectively). The KA-induced seizures in SRS rats differ behaviorally from KA-induced seizures in naive rats-namely, neither wet-dog shakes nor the status epilepticus could be induced. 3. Repeated injection of an equal dose of KA, applied to the SRS rats 1 day after the previous KA challenge, did not induce seizures. The loss of seizure susceptibility to KA was only temporary, as shown after a 7-day drug-free period, when the repeated injection of KA regained its seizure-triggering capacity. 4. The results indicate that reactivity to the seizure-inducing agent kainic acid changes in rats with spontaneous recurrent seizures.     

Gestational age-dependent extravillous cytotrophoblast osteopontin immunolocalization differentiates between normal and preeclamptic pregnancies

We examined the effect of 7-nitroindazole (7NI), a reportedly relatively specific inhibitor of the neuronal isoform of nitric oxide synthase (nNOS), on mean arterial blood pressure and on cerebral blood flow in rats under three different types of anaesthesia: urethane-chloralose, halothane, or urethane preceded by induction of anaesthesia with halothane. In rats under urethane-chloralose anaesthesia, 7NI induced an increase in mean systemic arterial blood pressure. In contrast, halothane used for induction and maintenance of anaesthesia eliminated the 7NI-induced systemic pressor effect, while halothane used only for induction of anaesthesia greatly attenuated the 7NI-induced systemic pressor effect. Cerebral blood flow, as measured by Laser Doppler flowmetry, decreased significantly to 85-72% of baseline within 5-10 min after i.p. 7NI injection regardless of the type of anaesthesia. Blockade of the systemic pressor effect of 7NI by halothane but not of the reduction in cerebral blood flow produced by 7NI is consistent with prior evidence that: (1) the cerebral vasculature and the peripheral vasculature differ in the isoforms of NOS involved in maintaining vascular tone, with nNOS more important in the former and endothelial NOS (eNOS) in the latter; and (2) halothane interferes with eNOS-mediated vascular tone but not nNOS-mediated control of cerebral blood flow. The fact that 7NI yields a pressor effect that can be attenuated by halothane, as also true for isoform-non-selective NOS inhibitors, raises the possibility that 7NI may to some extent inhibit endothelial NO formation. (c) 1998 The Italian Pharmacological Society.     

Hippocampal AMPA and NMDA mRNA levels and subunit immunoreactivity in human temporal lobe epilepsy patients and a rodent model of chronic mesial limbic epilepsy

This study compared temporal lobe epilepsy patients, along with kindled animals and self sustained limbic status epilepticus (SSLSE) rats for parallels in hippocampal AMPA and NMDA receptor subunit expression. Hippocampal sclerosis patients (HS), non-HS cases, and autopsies were studied for: hippocampal AMPA GluR1-3 and NMDAR1&2b mRNA levels using in situ hybridization: GluR1, GluR2/3, NMDAR1, and NMDAR2(a&b) immunoreactivity (IR); and neuron densities. Similarly, spontaneously seizing rats after SSLSE, kindled rats, and control animals were studied for: fascia dentata neuron densities: GluR1 and NMDAR2(a&b) IR; and neo-Timm's staining. In HS and non-HS cases, the mRNA hybridization densities per granule cell, as well as molecular layer IR, showed increased GluR1 (relative to GluR2/3) and increased NMDAR2b (relative to NMDAR1) compared to autopsies. Likewise, the molecular layer of SSLSE rats with spontaneous seizures demonstrated more neo-Timm's staining, and higher levels of GluR1 and NMDAR2(a&b) IR compared to kindled animals and controls. These results indicate that hippocampal AMPA and NMDA receptor subunit mRNAs and their proteins are differentially increased in association with spontaneous, but not kindled, seizures. Furthermore, there appears to be parallels in fascia dentata AMPA and NMDA receptor subunit expression between HS (and non-HS) epileptic patients and SSLSE rats. This finding supports the hypothesis that spontaneous seizures in humans and SSLSE rats involve differential alterations in hippocampal ionotrophic glutamate receptor subunits. Moreover, non-HS hippocampi were more like HS cases than hippocampi from kindled animals with respect to glutamate receptors; therefore, hippocampi from kindled rats do not accurately model human non-HS cases, despite some similarities in neuron densities and mossy fiber axon sprouting.     

Contribution of endogenous endothelin-1 to the maintenance of vascular tone: role of nitric oxide

Studies were designed to compare the effect of the nitric oxide inhibitor, N omega-nitro-L-arginine (L-NNA), and the novel ETB receptor antagonist, RES-701-1, on changes in blood pressure and renal blood flow induced by exogenous endothelin receptor agonists and to determine the effect of L-NNA on basal hemodynamics in conscious, chronically instrumented rats. Infusion of low (nonpressor) doses of L-NNA or RES-701-1 potentiated systemic and renal vasoconstriction induced by bolus injections of endothelin-1 or sarafotoxin 6c. Bolus intravenous injection or sustained infusion of L-NNA alone resulted in dose-dependent increases in blood pressure and decreases in renal blood flow, similar to our recently reported results with RES-701-1. Vasoconstriction induced by inhibition of nitric oxide was attenuated by SB 209670, a mixed ETA/B receptor antagonist, but not by BQ123, an ETA receptor antagonist; neither antagonist altered basal hemodynamics. Collectively, the results indicate that: (1) endothelin plays an important role in the control of basal vascular tone by mediating both vasodilation and vasoconstriction; (2) these effects are mediated by different ETB receptor subtypes in the rat, one located on the endothelium that mediates vasodilation via the nitric oxide pathway, the other located on the vascular smooth muscle that mediates contraction.     

Puerarin inhibits tetrodotoxin-resistant sodium current in rat dorsal root ganglion neurons

The effect of 7-nitroindazole (7-NI), an inhibitor of neuronal nitric oxide synthase (nNOS) on the dimethylphenylpiperazinium(DMPP)-evoked release of [3H]noradrenaline ([3H]NA) from rat hippocampal slices was studied. The effect of DMPP (20 microM) to increase the basal release of [3H]NA was significantly potentiated by 7-NI (40 microM). In our previous study we showed that the response to DMPP has two components, a nicotinic receptor-mediated, [Ca2+]-dependent exocytosis followed by a [Ca2+]-independent, uptake blocker-sensitive carrier-mediated release. To clarify which part of the response was affected by the inhibition of nNOS, we investigated the effect of 7-NI on the nicotine-evoked NA release (nicotine has only receptor-mediated effect) and on the DMPP-evoked NA release in Ca(2+)-free medium where the receptor-mediated component is abolished. Nicotine (100 microM) significantly increased the basal release of [3H]NA but this release was not affected, whereas in Ca(2+)-free medium the response to DMPP (20 microM) was still potentiated by 7-NI (40 microM). In the presence of the NA uptake blocker desipramine (10 microM) DMPP (20 microM) was unable to provoke NA release independently from the presence or absence of 7-NI (40 microM). Our data show that 7-NI influences the carrier-mediated component of DMPP-evoked [3H]NA release, which indicates that nitric oxide produced by nNOS may play a role in the regulation of the NA uptake carrier.     

Effects of neonatal status epilepticus on rat brain development

A single, 2-hour episode of status epilepticus induced by flurothyl (1,500 mul) in 4-day-old rats irreversibly curtailed brain weight and brain DNA. Status epilepticus inhibited DNA synthesis but did not increase DNA breakdown and produced no histologic lesions. Rats with status epilepticus showed delayed behavioral milestones and reduced seizure thresholds several weeks after status. After milder convulsions (flurothyl 750 mul, bicuculline), brain DNA was curtailed at 7 days but returned to normal at 30 days. These results suggest that, in the immature brain, epileptic seizures too mild to cause cell necrosis can inhibit DNA synthesis and permanently curtail brain DNA content. This may account for the great vulnerability of the immature brain to epileptic seizures.