l-NAME inhibits pentylenetetrazole and strychnine-induced seizures in mice

Nitric oxide (NO) formation has been shown in many neuronal tissues subserves a variety of functions. N-Methyl-d-aspartate (NMDA) receptor stimulation which releases nitric oxide and raises cGMP levels, mediates epileptiform activity induced by various agents. Disinhibition of inhibitory neurotransmitter γ-aminobutyric acid (GABA) and/or activation of NMDA receptor appears to be factors involved in the initiation and generalization of the pentylenetetrazole (PTZ) induced seizures. In the present study, we examined the effects of N^ω-nitro-l-arginine methylester (l-NAME) which inhibits nitric oxide synthase, on PTZ and strychnine induced seizures in mice. l-NAME (100 mg/kg) significantly prolonged the onset time of tonic generalized extension without affecting myoclonic jerks and tonic-clonic convulsions. l-NAME (200 mg/kg) significantly delayed three characteristic behavioral changes including first myoclonic jerk (FMJ), generalized clonic seizure (GCS) and tonic generalized extension (TGE). The effects of l-NAME were reversed by l-arginine (1000 mg/kg). l-NAME (100 and 200 mg/kg) significantly delayed the onset time of strychnine induced TGE. The effects of both doses of l-NAME were reversed by l-arginine. In conclusion, our results demonstrate that NO synthase inhibition suppresses the onset time of PTZ and strychnine induced seizures. Under the light of our current knowledge NO synthase inhibitors seem far away to be considered as a group of antiepileptic drugs. On the other hand there are some strong evidences about the role of NO in central pathophysiological mechanisms. © 1997 Elsevier Science B.V. All rights reserved.     

Effects of Central Injection of Kyotorphin and l-Arginine on Oxytocin and Vasopressin Release and Blood Pressure in Conscious Rats

Intracerebroventricular (ICV) administration of an inhibitor of nitric oxide synthase (NOS) increases oxytocin but not vasopressin secretion, in dehydrated rats [38]. Surprisingly, central injection of l-arginine, the substrate for NOS, caused a similar effect. Kyotorphin (l-tyrosyl-l-arginine), a dipeptide formed from l-arginine by kyotorphin synthetase in the brain may mediate this magnocellular response. Therefore, the dose and time responses of hormone release were compared following ICV injection of kyotorphin and l-arginine to conscious rats that were normally hydrated or deprived of water for 24 h. In water-sated rats, both l-arginine and kyotorphin increased blood pressure and plasma glucose levels coincident with elevating circulating levels of oxytocin, but not vasopressin. In dehydrated animals, both l-arginine and kyotorphin increased plasma oxytocin levels with a similar time course but only kyotorphin decreased vasopressin release. d-arginine, like l-arginine, stimulated secretion of oxytocin, indicating a nonstereospecific effect. A kyotorphin receptor antagonist (l-leucyl-l-arginine) given ICV to dehydrated animals elevated plasma oxytocin and prevented the decrease in vasopressin levels after kyotorphin. Thus, kyotorphin, but not l-arginine, appears to attenuate release of vasopressin either directly from magnocellular neurons or indirectly via modulating compensatory reflexes activated by the pressor response. On the other hand, an excess of l-arginine and kyotorphin within the CNS may mimic the stress response by augmenting release of oxytocin and activating the sympathetic nervous system to increase blood pressure and plasma glucose levels.     

l-DOPA metabolism in cortical and striatal tissues in an animal model of Parkinsonism

Rats with unilateral 6-hydroxydopamine lesions of the midbrain tegmentum were treated with 25 mg/kg l-DOPA methyl ester/2 mg/kg carbidopa. The effects of the l-DOPA treatment upon serum, neocortical, and striatal l-DOPA and 3-O-methyl dopa (3-OMD) concentrations were measured. The highest l-DOPA and 3-OMD concentrations were obtained in the serum and in a ratio of approximately 2:1. In the brain, there was a uniform distribution of 3-OMD but l-DOPA concentrations were highly nonhomogeneous. Regression line equations for the statistically significant correlation coefficients between l-DOPA and tissue dopamine concentrations suggested that l-DOPA generated 50–60 times as much dopamine in the intact striatum as in cortex. The regional variation of l-DOPA concentration appears related to the capability of the brain tissue to generate and store dopamine from l-DOPA. In addition, the findings suggest that the behavioral ineffectiveness of l-DOPA in intact animals is related to its capacity to transform l-DOPA to tissue bound dopamine.     

Chronic administration of l-NAME in drinking water alters working memory in rats

To examine the role of nitric oxide (NO) in the maintenance of working memory of rats, the effects of chronic administration (in drinking water) of the NO synthase inhibitor, N^w-nitro-l-arginine methyl ester (l-NAME), on this behavior was examined with a simple test of remembering recently explored objects. Unlike other working memory tasks that require a subject to perform for a reward such as food or water or to avoid shock, our task measured spontaneous exploration of novel and familiar objects and has been described as a “pure” working memory task [9]. Normal subjects spend significantly more time in contact with new environmental components and less time with familiar objects. A subject that extensively reexplores a stimulus with which it has previous experience is presumed to exhibit some memory loss associated with the object. Memory changes were evaluated by measuring the relative time subjects explored familiar versus new stimulus objects. Rats (n = 15) that chronically drank l-NAME (≈ 90 mg/kg/day) for 14 days spent significantly less time exploring a novel object than did rats (n = 13) that drank only tap water (p < .05). This effect of t.-NAME was abolished by concurrent administration of l-Arginine (≈ 4.5 g/kg/day). Total object exploration was not affected by our drug treatments, suggesting that our object discrimination task is not activity dependent. These data are consistent with the hypothesis that NO is required for some forms of working memory.     

Behavioral symptoms in adult rats after postnatal l-nitro-arginine

We addressed experimentally the suggestion by Gally et al. [Gaily J. A., Read Montague P., Reeke G. N. Jr and Edelman G. M. (1990) Proc. Natl Acad. Sci. U.S.A.87, 3547–3551] that nitric oxide may play a role in the use-dependent modification of synaptic efficacy in the developing nervous system. In a preliminary control experiment, we treated rat pups from postnatal day 8 to postnatal day 22 with a nitric oxide synthase blocker (l-nitro-arginine) and compared their growth curves and brain weights to those of saline injected control pubs. No significant differences were found after the 14 days of nitric oxide synthase inhibition. In the subsequent experiment, we inhibited nitric oxide synthesis in rat pups from postnatal day 8 to day 29 and assessed their place learning ability and open field behavior as adults. We found an increased speed of habituation of locomotion in an open field in 5-month-old rats that had been treated postnatally with a nitric oxide synthase blocker. There was no difference between treated and nontreated rats with respect to place learning in a water maze. We conclude that perturbation of nitric oxide production during early postnatal development does not preclude normal learning and memory function in the adult.     

Free d-serine concentration in normal and Alzheimer human brain

We have analyzed both free l- and d-serine in frontal cortex of normal and Alzheimer human brain by high-performance liquid chromatography (HPLC). There was no significant difference between the two brains. In normal brain, l- and d-serine concentrations were 666 ± 222 and 66 ± 41 nmol/g of wet tissue, respectively, and the ratio of d-isomer to l-isomer () was 0.099 ± 0.031. In Alzheimer brain, the concentrations were 750 ± 150 and 66 ± 40 nmol/g, respectively, and the ratio was 0.086 ± 0.040. Thus, it was shown that the free d-serine concentration in the Alzheimer brain was comparable to that in the normal brain.     

Exogenousl-5-hydroxytryptophan is decarboxylated in neurons of the substantia nigra pars compacta and locus coeruleus of the rat

The aim of the present study is to examine by immunohistochemistry whether exogenousl-5-hydroxytryptophan (l-5HTP) is decarboxylated in neurons of the substantia nigra pars compacta (SNC) and locus coeruleus (LC) of the rat. In normal rats, neurons of the SNC and LC stained intensely for aromaticl-amino acid decarboxylase (AADC). No serotonin (5HT)-positive cells were found in the two regions of the normal rats. In rats that were intraperitoneally injected withl-5HTP alone, the SNC neurons stained deeply for 5HT, but the LC neurons showed only a faint staining for 5HT. In rats that intraperitoneally received both a monoamine oxidase (MAO) inhibitor andl-5HTP, when compared with thel-5HTP-injected rats, the LC neurons became much darker in 5HT staining, but the SNC neurons showed only a slight increase in 5HT staining. The present findings suggest that (i) AADC in dopaminergic neurons of the SNC and in noradrenergic neurons of the LC can catalyze the in vivo decarboxylation of exogenousl-5HTP to produce 5HT, and (ii) most of the newly produced 5HT in the LC neurons is rapidly degraded by endogenous MAO.     

Responses of forebrain neurons to the MAO-B blocker l-deprenyl

Despite the large amount of neuropharmacological data concerning catecholamine (CA) mechanisms of the mammalian brain, little is known yet about the effects of MAO-inhibitors on single neurons. The present series of experiments aim to elucidate these specific neurochemical attributes of forebrain cells. Single neuron activity was recorded by means of multibarreled microelectrodes in the caudate nucleus, globus pallidus, and amygdala of both anesthetized rats and anesthetized or alert monkeys during microelectrophoretic application of the MAO-B blocker L-deprenyl (DEPR). CAs (dopamine and noradrenaline), glutamate, GABA, and acetylcholine were also applied. Nearly the half (46%) of all forebrain neurons tested responded, exclusively with inhibition, to DEPR, and the CA-sensitive cells were especially responsive to the MAO-B inhibitor. The time course of DEPR-induced neuronal suppression was short. In some cases, amphetamine (AMPH) and clorgyline (CLOR) were also applied microelectrophoreticaly. AMPH elicited similar activity changes to those seen after DEPR administrations, whereas CLOR applications were less effective. Our results provide evidence that DEPR can effectively modulate the activity of CA-sensitive neurons in the three different forebrain regions of two different species. On the basis of this data, the possible neurochemical mechanisms of DEPR action are discussed.     

Differential effects of NMDA and non-NMDA antagonists on the activity of aromatic l-amino acid decarboxylase activity in the nigrostriatal dopamine pathway of the rat

This study examined the acute effects of a variety of NMDA and non-NMDA antagonists on the activity of aromatic l-amino acid decarboxylase (AADC) in the corpus striatum (CS) and substantia nigra (SN) of the rat. Sixty min pretreatment with the high affinity NMDA receptor-channel blockers MK 801 (0.01, 0.1 and 1 mg/kg) and phencyclidine (4 mg/kg) elevated AADC activity in both the CS and SN (2- to 3-fold). Even more striking increases in AADC were noted with 40 mg/kg amantadine (3.8-fold for CS, 9.0-fold for SN), 40 mg/kg memantine (3.4-fold for CS, 3.1-fold for SN; 20 mg/kg no effect) and 40 mg/kg dextromethorphan (3.4-fold for CS, 6.2-fold for SN, in 6/10 `responders'). Similarly pronounced increases in AADC activity in CS (1.9-fold) and SN (2.8-fold) were detected after administering clonidine (2 mg/kg). R-HA 966 (5 mg/kg, not 1 mg/kg) modestly raised AADC activity in CS (0.45-fold) and not SN. Other drugs had no effect on the activity of the decarboxylase enzyme, including CGP 40116 (1 and 5 mg/g), eliprodil (10 mg/kg), NBQX (10 mg/kg, 30 min pretreatment) and atropine (1 mg/kg). These experiments indicate that blocking the NMDA receptor-channel (and to a lesser extent the glycine site) or stimulating α₂-adrenoceptors, profoundly increases AADC activity, more especially in the SN than CS. By contrast, inhibiting the NMDA glutamate recognition or polyamine sites, AMPA or muscarinic receptors is without effect on AADC in either brain region. The ability of amantadine and memantine to potentiate the antiparkinsonian actions of l-DOPA in the clinic, may be due to facilitated decarboxylation of l-DOPA by the brain.     

l-Arginine ameliorates cerebral blood flow and metabolism and decreases infarct volume in rats with cerebral ischemia

Effects ofl-arginine, 300 mg/kg, i.p., on the regional cerebral blood flow (rCBF), brain metabolism, and infarct volume were examined in spontaneously hypertensive rats subjected to occlusion of both left middle cerebral artery and left common carotid artery. Rats treated withl-arginine had higher rCBF, determined by hydrogen clearance method, in the ischemic core (7 ± 1 ml/100 g/min, mean ± S.E.M.) and penumbral regions (16 ± 2) than did rats treated with saline (5 ± 0 and 7 ± 1, respectively). Simultaneously,l-arginine attenuated metabolic derangement in the ischemic tissue at 60 min, i.e. well maintained adenosine triphosphate (ATP) in ischemic region (1.29 ± 0.07 mmol/kg inl-arginine group vs. 1.05 ± 0.06 in saline group), and also close to normal levels in ATP (2.61 ± 0.02 mmol/kg vs. 2.45 ± 0.05), glucose (2.29 ± 0.12 mmol/kg vs. 1.80 ± 0.17) and lactate (1.63 ± 0.10 mmol/kg vs. 2.24 ± 0.21) in periischemic region. In another experiment, the effects ofl-arginine on rCBF in the subcortical regions and on infarct volume were evaluated.l-arginine, compared with saline, increased rCBF by 8 ml/100 g/min in the ischemic side and reduced infarct volume by 29% at 24 h of ischemia. These findings support thatl-arginine may be potentially useful for the treatment of acute cerebral ischemia.     

Trihexyphenidyl Potentiation ofl-DOPA: Reduced Effectiveness Three Years Later in MPTP-Induced Chronic Hemiparkinsonian Monkeys

The effects of a combination of trihexyphenidyl andl-DOPA methyl ester given i.m. were studied 3–5 years after MPTP induced hemiparkinsonism in five female adultMacaca nemistrinamonkeys. Three years later, these studies were repeated to determine if the drug combination was equally effective. Although the combination of trihexyphenidyl andl-DOPA produced potentiation in both studies, 3 years later it was quantitatively less. This was due primarily to the reduced effectiveness ofl-DOPA methyl ester in a dose of 12.5 mg/kg i.m. Even though the combination was less effective in subsequent years, the animals continued to show the same clinical signs of hemiparkinsonism. Reduced effectiveness of the drug combination does not appear to be due to a lessening of MPTP-induced hemiparkinsonism, but rather to the reduced effectiveness ofl-DOPA.     

Failure of glycine site NMDA receptor antagonists to protect againstl-2-chloropropionic acid-induced neurotoxicity highlights the uniqueness of cerebellar NMDA receptors

Cultured cerebellar granule cells and cerebellar slices from neonatal rats have been widely used to examine the biochemistry of excitatory amino acid-induced cell death mediated in part by the activation of NMDA receptors. However, the NMDA subunit stoichiometry, producing functional NMDA receptors is different in cultured granule cells, neonatal and adult rat cerebellum as compared to the NMDA receptors in forebrain regions. We have used thel-2-chloropropionic acid (l-CPA) (750 mg/kg) model of NMDA-medialed selective cerebellar granule cell necrosis in vivo to examine the role of the glycine binding site and possible effect of the NR2C subunit (which is largely expressed only in the cerebellum) on granule cell necrosis. The abilities of various NMDA receptor antagonists were examined in vivo to determine the relative contribution of both glutamate and glycine sites involved in thel-CPA-induced neurotoxicity. The potent neuroprotective, non-competitive NMDA receptor antagonist dizocilpine (MK-801) was compared with glutamate and glycine site NMDA antagonists. We have examined a number of markers for thel-CPA-induced granule cell necrosis. Thel-CPA-induced reduction in cerebellar aspartate and glutamate concentrations were used as markers of granule cell necrosis. We also measured the cerebellar water content and sodium concentrations as measures of thel-CPA-induced cerebellar edema that accompanies the granule cell necrosis. Finally the ability of the NMDA antagonists to attenuate thel-CPA-induced reductions in body weight gain and the prevention of the loss in hindlimb function using a behavioral measure of hindlimb retraction were examined. The potent glutamate antagonists, CPP and CGP40116 and dizocilpine prevented thel-CPA-induced locomotor dysfunction and granule cell necrosis as measured by their ability to preventl-CPA-induced reductions in aspartate and glutamate concentrations. CPR CGP40116 and dizocilpine also prevented the appearance of cerebellar edema followingl-CPA administration. In addition, dizocilpine, CPP and CGP40116 were able to partially prevent thel-CPA-induced loss in body weight over the 48 h experimental period. In contrast, none of the glycine partial agonists or antagonists, namely (±)HA-966,d-cycloserine, MDL-29951, DPCQ, MNQX or L-701 252 were able to prevent thel-CPA-induced loss in body weight,l-CPA-induced granule cell necrosis and behavioral disturbances when administered to rats. None of the NMDA antagonists had any effect on the cerebellar neurochemistry when injected alone or had any effect on animal behavior except for dizocilpine, CPP, CGP401 l6 and (±)HA-966 which resulted in a transient sedation for between three and five hours immediately following their administration. In conclusion, we demonstrate that NMDA open channel blockade and glutamate antagonists can provide full neuroprotection against thel-CPA-induced granule cell necrosis. The failure of the glycine partial agonists and antagonists to provide any neuroprotection againstl-CPA-induced neurotoxicity in the cerebellum contrasts with their neuroprotective efficacy in other animal models of excitatory amino acid-induced cell death in forebrain regions in vivo. We therefore suggest that the glycine site plays a lesser role in modulating NMDA receptor function in the cerebellum and may explain why cells expressing NMDA receptors composed of NR1/NR2C subunits are particularly resistant to excitatory amino acid-induced neurotoxicity.     

Monoamine oxidase-dependent metabolism of dopamine in the striatum and substantia nigra of l-DOPA-treated monkeys

The effects of monoamine oxidase (MAO) inhibitors on the metabolism of dopamine synthesized from exogenous l-DOPA were investigated in the striatum and substantia nigra of squirrel monkeys. Administration of a single dose of l-DOPA (methyl ester, 40 mg/kg, i.p.) caused a significant increase in the levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) and in the DOPAC/dopamine ratio in the putamen, caudate and substantia nigra. These changes were more pronounced in the substantia nigra than in the striatum and within the striatum of l-DOPA-treated monkeys, levels of dopamine and its metabolites were higher in the putamen than in the caudate nucleus. When l-DOPA treatment was preceded by the injection of clorgyline or deprenyl at a concentration (1 mg/kg) which selectively inhibited MAO A or MAO B, respectively, striatal dopamine was increased while the striatal DOPAC and HVA levels and DOPAC/dopamine ratio were significantly reduced as compared to the values obtained with l-DOPA alone. The two MAO inhibitors also counteracted the increase in the DOPAC and HVA levels and DOPAC/dopamine ratio induced by l-DOPA in the substantia nigra. Thus, both MAO A and MAO B contribute to the metabolism of dopamine when higher levels of this neurotransmitter are generated from l-DOPA in the squirrel monkey. The extent of reduction of dopamine catabolism (as assessed by the decrease in DOPAC and HVA levels) in the striatum and substantia nigra was similar with clorgyline and deprenyl even if the ratio MAO A/MAO B was approximately 1 to 10. This indicates that, though catalyzed by both MAO A and MAO B, dopamine deamination following treatment with l-DOPA preferentially involves MAO A.     

N-methyl-d-aspartate stimulates dopamine release through nitric oxide formation in the nucleus accumbens of rats

Intracerebral microdialysis technique was utilized to study the effect ofN^G-nitro-l-arginine, a nitric oxide (NO) synthase inhibitor, onN-methyl-d-aspartate (NMDA)-induced dopamine overflow in the nucleus accumbens of unanesthetized, freely moving rats. Perfusion of 1 and 3 mM NMDA through the microdialysis probe dose-dependently increased the extracellular dopamine level in the nucleus accumbens. Coapplication of 0.5 mMd-(−)-2-amino-5-phosphonovaleric acid (D-AP5), a selective and competitive NMDA receptor antagonist, significantly reduced the dopamine overflow induced by 3 mM NMDA. Perfusion of 0.5 mMN^G-nitro-l-arginine alone did not affect the basal dopamine level, whereas it suppressed the NMDA-evoked dopamine overflow in the nucleus accumbens when concurrently applied with 3 mM NMDA. These results suggest that NO mediates, at least in part, dopamine release resulting from NMDA receptor activation in the nucleus accumbens of rats.     

Different mechanisms of l-arginine induced dilation of brain arterioles in normotensive and hypertensive rats

We evaluated the response of pial arterioles to l-arginine in anesthetized normotensive rats and spontaneously hypertensive rats equipped with a closed cranial window. Topical application of 10⁻⁶ − 10⁻⁴ mol/l l-arginine, which is known to be the endogenous substrate for the synthesis of nitric oxide, induced dose-dependent arteriolar vasodilation. The response was more pronounced in hypertensive than in normotensive rats (at the concentration of 10⁻⁴ mol/l l-arginine: 18.3 ± 3.3% vs. 6.7 ± 1.7%, respectively, means ± S.E.). The stereoisomer d-arginine had no effect in hypertensive rats. Topical application of the nitric oxide synthase inhibitor N-nitro-l-arginine converted l-arginine-induced dilation to constriction in normotensive and hypertensive rats. The cyclooxygenase inhibitor indomethacin (5 μg/ml cerebrospinal fluid) also blocked the dilation in both strains. Photochemical endothelial injury blocked l-arginine-induced dilation in normotensive rats, but only partly antagonized the response in hypertensive animals. Intravenous or topical pretreatment with the free radical scavenger superoxide dismutase significantly reduced the dilating response to 10⁻⁴ mol/l l-arginine in hypertensive rats. Superoxide dismutase did not significantly change the response to l-arginine in normotensive animals. It is concluded that nitric oxid formation in the endothelium and liberation of cyclooxygenase products cause l-arginine-induced dilation in normotensive rats. While nitric oxide and cyclooxygenase products are also involved in l-arginine-induced dilation in spontaneously hypertensive rats, superoxide radicals contribute to the enhanced response in this strain. This mechanism appears to be specific for the hypertensive animals and is only partly dependent on an intact endothelium.     

The partial dopamine agonist pardoprunox (SLV308) administered in combination with l-dopa improves efficacy and decreases dyskinesia in MPTP treated common marmosets

Dopamine agonist treatment in early Parkinson's disease (PD) induces less dyskinesia than l-dopa. However, once dyskinesia has developed, dopamine agonists administered with l-dopa exacerbate involuntary movements. The dopamine partial D2/D3 agonist pardoprunox reverses motor deficits in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP)-treated primates without hyperactivity, indicating that pardoprunox may alleviate dyskinesia without compromising l-dopa's beneficial actions. This study examines a clinical scenario in which pardoprunox was introduced, in an l-dopa sparing strategy, to existing l-dopa treatment in MPTP-treated marmosets previously primed to express dyskinesia. l-Dopa (5–10 mg/kg) produced effects, which were stable over the 13 treatment days, of increased locomotor activity, reversed motor disability and marked dyskinesia. Pardoprunox (SLV308; 0.0125–0.025 mg/kg) plus l-dopa (3–10 mg/kg) administration increased locomotor activity over the same treatment period and initially produced an equivalent reversal of motor disability compared to l-dopa, however this effect was enhanced as treatment progressed. This reflected the prolonged duration of effect of pardoprunox compared to that of l-dopa. While pardoprunox plus l-dopa treatment initially produced dyskinesia to the same extent as l-dopa alone, the intensity diminished as treatment progressed and it was significantly different at the end of the study. On subsequent l-dopa challenge there was no difference in motor disability reversal between those animals previously treated with pardoprunox plus l-dopa compared to l-dopa alone but the combination treatment produced significantly less dyskinesia. These data suggest that pardoprunox may provide therapeutic benefit in mid to late stage PD by reducing dyskinesia while maintaining efficacy when used with concomitant l-dopa treatment.     

Blockade of l-glutamate receptors in the rostral ventrolateral medulla contributes to ethanol-evoked impairment of baroreflexes in conscious rats

This study investigated the effect of ethanol microinjected into the rostral ventrolateral medulla on the cardiovascular responses to in6arostral ventroleteal medulla administration of the excitatory amino acids l-glutamate and N-methyl-d-aspartate (NMDA) and on baroreflex-mediated heart rate responses (baroreflex sensitivity) in conscious freely moving Sprague-Dawley rats. l-Glutamate (5 nmol) or NMDA (25, 50, and 100 pmol) microlrjected into the rostral ventrolateral medulla elicited pressor and bradycardic responses. The cardiovascular responses elicited by both l-glutamate and NMDA were significantly (p < 0.05) attenuated by intrarostrel ventrolateral medulla ethanol (10 μg) or 2-amino-5 acid (2 nmoq, a selective NMDA receptor antagonist, but not by ACSF. Enhancement of the cardiovascular responses to l-glutamate by intrarostra ventrolateral medulla p-chloromercuriphenylsulfonic acid (0.1 nmol), a glutamate uptake inhibitor, was reversed by subsequent ethanol, but not ACSF, microinjection. None of the treatments influenced baseline blood pressure or heart rate. Ethanol or 2-amino-5-phosphonopentanoic acid microinjected into the rostral ventrolateral medulla significantly (p < 0.05) attenuated baroreflex sensitivity tested by phenylephrine. In contrast, p-chloromercuriphenylsulfonic acid significantly (p < 0.05) enhanced baroreflex sensitivity (−2.14 ± 0.09 vs. −3.08 ± 0.18); subsequent ethanol micoinjection reversed this enhancement (−290 ± 0.21 vs. −1.86 ± 0.24). Equal volume of ACSF had no effect on baroreftex sensitivity of pretreated rats (−3.22 ± 0.31 vs. −2.98 ± 0.34). These results suggest that ethanol exerts a marked inhibitory action on glutamatergic pathways within the rostral ventrolateral medulla that act to enhance baroreftex sensitivity. The similarities between the inhibitory actions of ethanol and the selective NMDA receptor Mocker 2-amino-5-phosphonopentanoic acid on the cardiovascular responses to NMDA and on baroreflex sensitivity suggest that ethanol attenuates baroreflex sensitivity, at least in part, by blocking the NMDA receptors in the rostral ventrolateral medulla. This evidence is presented, for the first time, in the absence of the confounding effects of anesthetics.     

Aromatic L-amino acid decarboxylase is present in serotonergic fibers of the striatum of the rat. A double-labeling immunofluorescence study

The aim of the present study is to examine whether serotonergic fibers of the striatum of the rat contain aromaticl-amino acid decar?ylase (AADC). By use of a double-labeling immunofluorescence method, we showed that AADC was localized in serotonergic fibers of the striatum and cerebral cortex as well as in serotonergic cell bodies of the midbrain raphe nuclei. We previously demonstrated that serotonergic fibers of the rat striatum contained dopamine after intraperitoneal injection ofl-dopa. These findings suggest that dopamine is produced from the injectedl-dopa in serotonergic fibers of the rat striatum.     

Short-photoperiod exposure reduces l-aromatic-amino-acid decarboxylase immunostaining in the arcuate nucleus and median eminence of male Syrian hamsters

In male hamsters, exposure to short photoperiod (SD) results in a decrease in median eminence and posterior pituitary dopamine (DA) concentrations. To determine if the SD-induced decline in DA is due to a decrease in the number of neurons synthesizing DA, immunocytochemistry was used to identify cells containing tyrosine hydroxylase (TH) and l-aromatic amino acid decarboxylase (AADC) in animals housed under long photoperiod (LD) or SD. Immunopositive cells were counted in the arcuate and caudal periventricular nuclei, regions where the DA neurons that project to the median eminence and posterior pituitary are located. AADC immunopositive (AADC + ) cells were also counted in the median eminence. Photoperiod did not affect the number of TH immunopositive (TH + ) or AADC + cells in the caudal periventricular nuclei. In the arcuate nuclei, SD exposure did not affect the number of TH + neurons, but produced a significant decline in the number of AADC + cells. The number of AADC + cells was also reduced in the median eminence of SD-exposed animals. This decline in AADC + cells may play a role in SD-induced changes in hypothalamic regulation of anterior pituitary hormone release, including the decline in median eminence DA concentrations.