L. Berrino

Interaction between vanilloid and glutamate receptors in the central modulation of nociception.

This study investigates the effect of microinjections of capsaicin in the periaqueductal grey matter of rats on nociceptive behaviour and the possible interactions with NMDA and mGlu receptors. Intra-periaqueductal grey microinjection of capsaicin (1-3-6 nmol/rat) increased the latency of the nociceptive reaction in the plantar test. This effect was prevented by pretreatment with capsazepine (6 nmol/rat), which had no effect per se on the latency of the nociceptive reaction. 7-(Hydroxyimino)cyclopropa[b]chromen-1alpha-carboxylate ethyl ester (CPCCOEt, 50 nmol/rat) and 2-Methyl-6-(phenylethynyl)pyridine (MPEP, 50 nmol/rat), antagonists of mGlu(1) and mGlu(5) receptors, respectively, completely blocked the effect of capsaicin. Similarly, pretreatment with DL-2-Amino-5-phosphonovaleric acid (DL-AP5, 5 nmol/rat) and riluzole (4 nmol/rat), an NMDA receptor antagonist and a voltage-dependent Na(+) channels blocker which inhibits glutamate release, respectively, completely antagonized the effect of capsaicin. However, pretreatment with (2S)-alpha-Ethylglutamic acid (30 nmol/rat) and (RS)-alpha-Methylserine-O-phosphate (MSOP, 30 nmol/rat), antagonists of group II and group III mGlu receptors, respectively, had no effects on capsaicin-induced analgesia. Similarly, pretreatment with N-(piperidin-1-yl)-5-(4-chlophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR 141716A, 5 pmol/rat), a selective cannabinoid CB(1) receptor antagonist, did not affect the capsaicin-induced antinociception. In conclusion, this study shows that capsaicin might produce antinociception at the periaqueductal grey level by increasing glutamate release, which activates postsynaptic group I mGlu and NMDA receptors.

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.

Periaqueductal gray area and cardiovascular function.

The periaqueductal gray (PAG) area seems to play an important role in modulating several biological functions such as the triggering of stereotyped defence and reproductive behaviour, pain, anxiety and cardiovascular and respiratory activities. Anatomically this midbrain area is made up of symmetric neuronal columns arranged along the long axis of the aqueduct. In this paper we review the most important findings of the last 10-15 years about the interaction between the PAG area and the cardiovascular function. It is shown that these neuronal columns within the PAG area exhibit a viscerotropic organization which elicits both hypertensive and hypotensive responses. In particular, the stimulation of the ventral neuronal column evokes a hypotensive response associated with a regional decrease in the vascular resistance. On the contrary, the stimulation of the dorsal and lateral neuronal columns evokes arterial hypertension associated with specific changes of the vascular resistance. Recently the authors demonstrated that the glutamergic system in the PAG area (prevalently through NMDA subtype receptor) may also be involved in the control of cardiovascular system. Moreover, the involvement of the arginine vasopressin neuropeptide in the hypertension induced by administration of excitatory amino acids into the PAG area has been demonstrated.

Nitric oxide participates in the hypotensive effect induced by adenosine A2 subtype receptor stimulation.

In a previous study, we demonstrated that adenosine plays an important role in the central control of the cardiovascular system with involvement of adenosine A2 rather than A1 subtype receptors. In the present study, we investigated the putative relationship between nitric oxide (NO) and adenosine in the central and peripheral control of the cardiovascular system. Adult male nor-motensive anesthetized rats were treated with N6-cyclohexyladenosine (CHA), an A1-punnoceptor agonist, and 5‘-N-cyclopropyl-carboxamidoadenosine (CPCA), an A2-purinoceptor agonist intracerebroventricularly (i.c.v. 3rd ventricle; 0.05–0.1–0.5 μg/rat) and by intravenous injection (0.5–1-5 μg kg−1 i.v.). CPCA and CHA induced a significant and dose-dependent decrease in arterial blood pressure (BP). CHA effects were less marked than CPA. Rats were pretreated with xanthine amine congener (XAC), and A1 adenosine antagonist, with 3,7-dimethyl-1-propargylxanthine (DMPX), an A2 adenosine antagonist (both administered at doses of 0.05 μg/rat i.c.v. or 0.5 μg kg−1 i.v.) and with N+-nitro-L-arginine methyl ester, an NO synthase inhibitor, (L-NAME, 90 μg/rat i.c.v. and 0.3 mg kg−1 i.v.). The intracerebroventricular and intravenous pretreatment with DMPX or L-NAME inhibited CPCA-induced hypotension; the effect of L-NAME was weaker than that of DMPX. The L-NAME inhibitory effect was reversed both in the central nervous system (CNS) and at the peripheral level by pretreatment with L-arginine (L-Arg; 90 mg kg−1 i.v.), a precursor of NO synthesis. Pretreatment with XAC, but not with L-NAME, reduced the hypotensive effect of CHA. Moreover, intracerebroventricular pretreatment with L-Arg (174 μg/rat) increased the hypotensive effect of CPCA. These results suggest that NO partially mediates the hypotensive effect induced by A2 subtype receptors stimulation in the CNS and at a peripheral level.

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.

Effects of docosahexaenoic acid on calcium pathway in adult rat cardiomyocytes

In this study we examined the effect of polyunsaturated fatty acids (PUFAs), in particular of docosahexaenoic acid (DHA), on calcium homeostasis in isolated adult rat cardiomyocytes exposed to KCl, ET-1 and anoxia. Free [Ca(2+)](i) in rat cardiomyocytes was 135.7 +/- 0.5 nM. Exposure to 50 mM KCl or 100 nM ET-1 resulted in a rise in free [Ca(2+)](i) in freshly isolated cells (465.4 +/- 15.6 nM and 311.3 +/- 12.6 nM, respectively) and in cultured cells (450.8 +/- 14.8 nM and 323.5 +/- 14.8 nM respectively). An acute treatment (20 minutes) with 10 microM DHA significantly reduced the KCl- and ET-1-induced [Ca(2+)](i) increase (300.9 +/- 18.1 nM and 232.08 +/- 11.8 nM, respectively). This reduction was greater after chronic treatment with DHA (72 h; 257.7 +/- 13.08 nM and 192.18 +/- 9.8 nM, respectively). Rat cardiomyocytes exposed to a 20 minute superfusion with anoxic solution, obtained by replacing O(2) with N(2) in gas mixture, showed a massive increase in cytosolic calcium (1200.2 +/- 50.2 nM). Longer exposure to anoxia induced hypercontraction and later death of rat cardiomyocytes. Preincubation with DHA reduced the anoxic effect on [Ca(2+)](i) (498.4 +/- 7.3 nM in acute and 200.2 +/- 12.2 nM in chronic treatment). In anoxic conditions 50 mM KCl and 100 nM ET-1 produced extreme and unmeasurable increases of [Ca(2+)](i.) Preincubation for 20 minutes with DHA reduced this phenomenon (856.1 +/- 20.3 nM and 782.3 +/- 7.6 nM, respectively). This reduction is more evident after a chronic treatment with DHA (257.7 +/- 10.6 nM and 232.2 +/- 12.5 nM, respectively). We conclude that in rat cardiomyocytes KCl, ET-1 and anoxia interfered with intracellular calcium concentrations by either modifying calcium levels or impairing calcium homeostasis. Acute, and especially chronic, DHA administration markedly reduced the damage induced by calcium overload in those cells.

The role of A3 adenosine receptors in central regulation of arterial blood pressure

1 Pharmacological studies have suggested that A3 receptors are present on central neurons. Recently this adenosine receptor subtype has been identified in the rat and its presence in the central nervous system has been confirmed. 2 In this study we investigated the effects of acute intracerebroventricular (i.c.v.) injections of N6‐2‐(4‐aminophenyl)‐ethyladenosine (APNEA), a non‐selective A3 adenosine receptor agonist, on arterial blood pressure (ABP) and heart rate (HR), after treatment with 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX), a selective antagonist of A1 adenosine receptors. 3 Anaesthetized rats, after DPCPX (12 μg−1 kg i.c.v.), were treated with APNEA (0.4–4 μg kg−1 i.c.v.) resulting in a transitory and dose‐dependent decrease in arterial blood pressure without a change in heart rate. APNEA also induced hypotensive responses after i.c.v. pretreatment with aminophylline, at a dose of 20 μg kg−1. In contrast, pretreatment 48 h before, with 4 μg kg−1 i.c.v. of pertussis toxin reduced the hypotensive effect induced by APNEA. Administration of APNEA at a higher dose (20 μg kg−1 i.c.v.), after DPCPX, induced a decrease in ABP of −66±5.4 mmHg and after 3 min a decrease in heart rate of −62±6.0 beats min−1. Transection of the spinal cord abolished this significant fall in ABP, but not the decrease of HR. 4 These results suggest that a population of A3‐receptors is present in the CNS, whose activation induces a decrease in blood pressure with no change of heart rate.

Endothelin-1 in periaqueductal gray area of mice induces analgesia via glutamatergic receptors

&NA; The aim of the study was to examine whether endothelin‐1 (ET‐1) injected into dorsolateral periaqueductal gray (PAG) area of mice produces antinociception. ET‐1, from 1 to 4 pmol/mouse, induced antinociceptive effect in a dose‐dependent manner. This antinociceptive effect was prevented by NMDA receptor antagonists (2‐APV and MK‐801) injected in the same area (2‐APV) or by intraperitoneal route (MK‐801). CNQX, a non‐NMDA receptor antagonist, did not inhibit the ET‐1 effects. Prazosin, an &agr;1‐adrenergic blocking agent, also prevented the ET‐1 antinociceptive effect. We suggest that the activation of NMDA glutamatergic receptors in the PAG area may be a necessary step for ET‐1 induced antinociception.

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.