S. Vitagliano

Pregnenolone sulfate increases the convulsant potency of N-methyl-D-aspartate in mice

The neurosteroid pregnenolone sulfate is known to specifically enhance NMDA-gated currents in spinal cord neurons. The response does not appear to be mediated by the glycine/NMDA modulatory site. Here we found that pregnenolone sulfate significantly increased the convulsant potency of N-methyl-D-aspartate (NMDA), but not of pentylenetetrazol (PTZ). In agreement with previous in vitro reports showing that the glutamergic NMDA receptor is also specifically modulated by steroids, our findings suggest that pregnenolone sulfate selectively activates the NMDA receptors involved in convulsions in the intact animal.

Involvement of nitric oxide in cardiorespiratory regulation in the nucleus tractus solitarii

The aim of this study was to investigate whether nitric oxide (NO) is involved in cardiorespiratory regulation in the nucleus tractus solitarii (NTS). Unilateral microinjections (50 nl) of the NO-donor, sodium nitroprusside (SNP, 40-100-200 mM), into the NTS of anaesthetized rats elicited dose-dependent apnea (7.3 +/- 2.3 sec; 28.6 +/- 5.7 sec; 35.6 +/- 6.4 sec, respectively; n = 6) and a decrease in arterial blood pressure (8.4 +/- 3.1 mmHg; 18.2 +/- 5.8 mmHg; 25.8 +/- 6.7 mmHg, respectively; n = 6). Similarly, unilateral micro-injections (50 nl) of another NO-donor, 3-morpholinosydnonimine (SIN-1, 20-40-100 mM), also induced apnea (5.1 +/- 2.4 sec; 8.7 +/- 4.3 sec; 26.3 +/- 6.4 sec, respectively; n = 6) and a decrease in arterial blood pressure (6.2 +/- 2.3 mmHg; 11.1 +/- 3.3 mmHg; 18.3 +/- 6.1 mmHg, respectively; n = 6). The SNP- and SIN-1-induced apnea and arterial blood pressure decrease were significantly (p < 0.01) blocked by a 3 min pretreatment with two calcium-channel blockers, diltiazem (0.1 mM) and cobalt (10 mM), while lower doses (diltiazem 0.01 and cobalt 1) were ineffective. Microinjections of diltiazem (0.01 mM) and cobalt (1 mM) alone did not induce any change in basal cardiorespiratory values like diltiazem (0.1 mM) and cobalt (10 mM). These data suggest that NO may be involved in NTS cardiorespiratory regulation via calcium-channel activation.

Interactive role of L-glutamate and vasopressin, at the level of the PAG area, for cardiovascular tone and stereotyped behaviour.

The periaqueductal gray (PAG) area may modulate cardiovascular functions and trigger several stereotyped behavioural responses through a mechanism mediated by the interaction of L-glutamate with arginine vasopressin (AVP). Moreover, only the NMDA- but not the non-NMDA-glutamergic subtype receptors might participate in the control of these neurovegetative functions also modifying the homeostasis of the hypothalamic-neurohypophysis system. This latter effect may be due to the tight connections between the PAG area neurons to the more cephalic nuclei within the brainstem.

Endothelin-1 in Rat Periaqueductal Gray Area Induces Hypertension Via Glutamatergic Receptors

We investigated the possible relationship between endothelin-1 injection into the dorsolateral periaqueductal gray area and the glutamatergic system in the control of cardiovascular function. Endothelin-1 was injected into the dorsolateral periaqueductal gray area of freely moving rats at doses ranging from 0.1 to 10 pmol. Endothelin-1 increased arterial blood pressure (from 7.0 +/- 1.6 to 55.0 +/- 4.1 mm Hg, mean +/- SEM) in a dose-dependent manner and induced characteristic behavioral changes such as longitudinal rolling of the body (barrel-rolling). DL-2-Amino-5-phosphonovaleric acid and (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[D-alpha] cyclohepten-5,10-imine hydrogen maleate, both selective N-methyl-D-aspartate excitatory amino acid receptor antagonists, but not 6-cyano-7-nitroquinoxaline-2,3-dione, a non-N-methyl-D-aspartate excitatory amino acid receptor antagonist, significantly decreased endothelin-1-induced cardiovascular and behavioral changes (P < .01). Prazosin and propranolol, adrenergic blocking agents, and reserpine, a depletor of catecholamine stores, also prevented these effects. We propose that the glutamatergic system may exert, via N-methyl-D-aspartate receptors, a significant influence on endothelin-1-induced cardiovascular and behavioral effects after its injection into the periaqueductal area.

Metabotropic glutamate receptors are involved in the control of breathing at the medulla oblongata level of anaesthetized rats

The goal of the present study was to identify sites in the medulla oblongata where metabotropic glutamate receptors are involved in regulating respiration. Unilateral microinjections (50 nl) of L-glutamate (L-glu) (10-25-50 mM) into the nucleus tractus solitarii (NTS) of anaesthetized rats elicited apnea (8.6 +/- 0.3 sec; 21.3 +/- 3.6 sec; 66.3 +/- 16.5 sec respectively; N = 6) and arterial hypotension (7.3 +/- 2.4 mmHg; 10.1 +/- 2.3 mmHg; 35.3 +/- 7.5 mmHg respectively; N = 6). Similarly, in other rats 1-aminocyclopentane-1, 3-dicarboxylic acid (ACPD) (1-5-10 mM), a selective agonist of metabotrophic glutamate receptors, also induced apnea (22.4 +/- 2.5 sec; 32.5 +/- sec; 92.5 +/- 1.4 sec respectively; N = 6) and arterial hypotension (12.7 +/- 2.2 mmHg; 19.6 +/- 4.3 mmHg; 26.5 +/- 1.5 mmHg respectively; N = 6). Paired experiments showed that unilateral microinjections of L-glu (50 mM) and ACPD (1 mM) into the nucleus retroambigualis (NRA) of anaesthetized rats elicited apnea (20.2 +/- 2.6 sec and 33.8 +/- 3.2 sec respectively; N = 6) and arterial hypotension (15.7 +/- 3.7 mmHg and 22.5 +/- 4.5 mmHg respectively; N = 6). The ACPD effects on apnea and hypotension in NTS and NRA were not prevented by a 3 min pretreatment with L-AP3 (30 mM), a putative antagonist of metabotropic glutamate receptors (19.5 +/- 1.4 sec; 12.3 +/- 3.2 mmHg and 30.6 +/- 2.9 sec; 23.4 +/- 3.8 mmHg respectively; N = 6). These data suggest that metabotropic glutamate receptors are involved in NTS and NRA regulation of cardiorespiratory functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Participation of arginine vasopressin-mediated and adrenergic system-mediated mechanisms in the hypertension induced by intracerebroventricular administration of NMDA in freely moving rats.

Effects of intracerebroventricular (third ventricle) injection of N-methyl-D-aspartate (NMDA) on arterial blood pressure, on heart rate, on arginine vasopressin (AVP) and levels of catecholamines in plasma and on the behaviour of normotensive freely-moving rats have been evaluated. N-Methyl-D-aspartate significantly (P less than 0.01) increased arterial blood pressure and levels of catecholamines and AVP in plasma. With 0.1-1.0 micrograms/rat all animals presented psychomotor agitation, stereotyped movements, hyperexcitability, exophthalmus, dyspnoea, jumping, rearing and teething. The selective antagonist for NMDA receptors, 2-APV injected in the third ventricle, significantly (P less than 0.01) antagonized the hypertension, the increase in levels of catecholamines and AVP in plasma and behavioural effects. An antagonist of alpha 1 adrenergic receptors, prazosin (i.v.), an agonist of alpha 2 adrenergic receptors, clonidine (i.c.v.) and a relatively selective antagonist of V1 subtype of receptor of AVP, CGP 25838 (i.c.v. and i.v.), 15 min before NMDA, significantly (P less than 0.01) decreased the effects induced by the injections of NMDA. On the contrary, an antagonist of opiate receptors, naloxone (i.v.), 15 min before NMDA, significantly (P less than 0.01) increased the NMDA-induced modifications. Pretreatment with the antagonists at these doses, did not significantly modify the basal values of arterial blood pressure and behaviour. Only 2-APV sometimes induced ataxia, lasting about 5 min. This study points out an increase in the central sympathetic efferent activity and in release of AVP involved in the NMDA-induced cardiovascular and behavioural effects.

Hypothalamic paraventricular nucleus involvement in the pressor response to N-methyl-d-aspartic acid in the periaqueductal grey matter

The aim of this study was to demonstrate paraventricular hypothalamic nucleus (PVN) involvement in the cardiovascular changes induced by N-methyl-d-aspartic acid (NMDA) microinjections at the level of periaqueductal grey (PAG) matter. The study was carried out in anaesthetized rats and the arterial blood pressure monitored by a polygraph. NMDA injections (0.68–6.8 nmol/rat) into the PAG area induced a significant increase in blood pressure. After pretreatment by injection of the NMDA receptor antagonist dl-2-amino-5-phosphonovaleric acid (2-APV, 0.05-5 nmol/rat) into the PVN, administration of NMDA (0.68 nmol/rat) into the PAG area elicited a decrease, rather than an increase, of blood pressure. We observed a significant reduction of the pressor effect induced by 6.8 nmol/rat NMDA after 2-APV injection into the PVN. 2-APV injection into the dorsomedial hypothalamic nucleus, an area near the PVN, did not modify the increase in blood pressure induced by NMDA in the PAG area. We suggest the existence of a glutamatergic connection between the PAG area and the PVN in the cardiovascular effects of NMDA.

Modulation by glycine on vascular effect of NMDA: in vivo experimental researches.

SummaryThe present study has been carried out to determine if glycine, an allosteric modulator of NMDA receptor, is involved in the vascular effect induced by the activation of the CNS NMDA receptors.Icv NMDA (from 0.01 to 1µg/rat in the 3rd ventricle) determined a significant increase in arterial blood pressure in conscious freely moving rats. Moreover, the hypertension was associated with behavioural modifications (jumping, rearing, teething and running). Glycine pretreatment (1 and 10µg/raticv), significantly increased the NMDA hypertension. Alone glycine did not cause any arterial blood pressure modification while it induced a slight sedation. HA-966 (an antagonist of the glycine site on NMDA receptor) administration (1–10µg/raticv 5 min before glycine) significantly antagonized the glycine effects on NMDA hypertension.Alone HA-966 neither modified arterial blood pressure nor antagonized NMDA hypertension. In conclusion, our investigations confirm NMDA receptor involvement in cardiovascular function and they demonstrate that in vivo glycine positively modulates NMDA receptor.

Effects of the polyamine spermidine on NMDA-induced arterial hypertension in freely moving rats.

We investigated the effect of the polyamine spermidine (SPD) (0.01-1 microgram/rat) on hypertension induced by N-methyl-D-aspartate (NMDA) (0.1 microgram/rat) microinjected into the latero-caudal periaqueductal gray (PAG) area of freely moving rats. Pretreatment with a low dose of SPD (0.01 microgram/rat) significantly increased NMDA-induced hypertension. On the contrary, higher doses of SPD (0.1 and 1 microgram/rat) significantly decreased NMDA-induced cardiovascular changes. SPD alone did not modify arterial blood pressure. Arcaine (1 microgram/rat), a putative antagonist at the polyamine recognition site on NMDA receptors, when microinjected into the PAG area, prevented the negative but not the positive modulatory effects of SPD on the NMDA-induced cardiovascular changes. Pretreatment with SPD did not affect cardiovascular effects induced by quisqualic acid (QUIS), a non-NMDA receptor agonist. These data, in agreement with the in vitro results, suggest that at the level of the PAG area, the polyamines also show multiple actions at NMDA receptors in vivo.

Cobalt blocks l-glutamate-induced apnea and arterial hypotension in the nucleus tractus solitarii of anaesthetized rats

The local application of cobalt reversibly blocks calcium-channel conductance and therefore synaptic transmission. In this study pretreatment with a solution of cobalt (100 mM) in the nucleus tractus solitarii (NTS) of anaesthetized rats significantly blocked the apnea (P < 0.01) and arterial hypotension induced by L-glutamate (25 mM) and N-methyl-D-aspartate (0.4 mM) microinjected in the NTS. We conclude that cobalt causes these effects by acting at the postsynaptic level.