Nitric oxide induces calcium-dependent [3H]dopamine release from striatal slices

Effect of arginine on basal and high potassium-induced efflux of [3H]D-aspartate from rat striatal slices

There are conflicting reports in the literature regarding the effects of nitric oxide as well as the involvement of the cyclic GMP pathway on the transmitter release. To study the influence of the availability of the nitric oxide precursor arginine on the glutamate transmission process, rat striatal slices preloaded with the tritiated glutamate analogue D-aspartate were used. L-Arginine stimulated in a concentration-dependent way (0.01-10.0 mM) the high potassium-induced efflux of [3H]D-aspartate. The basal release was increased only by 10 mM L-arginine. Neither the basal nor the depolarization-induced efflux of [3H]D-aspartate was affected by D-arginine. The L-arginine effect was abolished by the nitric oxide synthase inhibitor L-arginine methyl ester and was not modified by cyclic GMP. Only at high concentrations of L-arginine (10 mM) could an elevation of cyclic GMP level be demonstrated. The results are discussed in terms of direct presynaptic action of nitric oxide on [3H]D-aspartate efflux and a possible modulation of glutamate release by the availability of arginine.

Contribution of endogenously formed arachidonic acid in the presynaptic facilitatory effects of NMDA and carbachol on dopamine release in the mouse striatum

Arachidonic acid stimulated the release of [3H]-dopamine from striatal microdiscs in a concentration-dependent and partially calcium-dependent manner. Inhibitors of cytosolic and membrane-bound phospholipase A2 were used to determine whether endogenously formed arachidonic acid also contributes to the release of [3H]-DA (previously taken up in tissues or endogenously synthesized from [3H]-tyrosine) evoked by N-methyl-d-aspartate (NMDA) and carbachol alone or in combination. In the presence of magnesium, carbachol was found to remove the magnesium block of NMDA receptors and to facilitate the NMDA-evoked release of [3H]-DA from striatal microdiscs and synaptosomes. In addition, in the absence of magnesium, synergistic responses were induced by both agonists on microdiscs but not on synaptosomes. Responses induced by NMDA, carbachol or both agonists on microdiscs were reduced by phospholipase A2 inhibitors, the most striking effects being observed with mepacrine. Mepacrine was also shown to reduce the oxotremorine, but neither the nicotine- nor the potassium-evoked release of [3H]-DA. Tetrodotoxin decreased the release of [3H]-DA evoked by the co-application of NMDA and carbachol on microdiscs, but mepacrine still decreased this tetrodotoxin-resistant response. Similarly, mepacrine still decreased the release of [3H]-DA evoked by NMDA and carbachol on synaptosomes. Altogether, these results indicate that arachidonic acid which is formed in striatal neurons, and to a lesser extent in DA fibres, under stimulation of NMDA and muscarinic receptors, partially contributes to the presynaptic facilitation of DA release evoked by NMDA and carbachol.

Basal ganglia neuronal nitric oxide synthase mRNA expression in Parkinson's disease

Expression of nitric oxide synthase (NOS) mRNA in post mortem brain was studied in putamen, globus pallidus and subthalamic nucleus (STN) of neurologically normal control subjects and patients with Parkinson's disease (PD) using in situ hybridization histochemistry. In PD, a significant increase in NOS mRNA expression was observed in the dorsal two-thirds of the STN with respect to the ventral one-third of the STN. A significant increase in NOS mRNA expression per cell in the medial medullary lamina of the globus pallidus was also observed in PD. NOS mRNA expression was significantly reduced in PD putamen. These findings provide evidence of increased activity of STN neurotransmitter systems in PD and demonstrate for the first time in any species that basal ganglia nitric oxide systems can be selectively regulated in response to changes in dopaminergic input.

Nitric oxide and potassium chloride-facilitated striatal dopamine efflux in vivo: role of calcium-dependent release mechanisms

Previous studies investigating the calcium-dependency of nitric oxide-facilitated striatal dopamine efflux have produced conflicting results. In the current study, we have investigated the role of extracellular calcium in nitric oxide and potassium chloride-evoked striatal dopamine efflux in vivo using microdialysis. Dialysis probes were implanted in the anterior dorsal striatum of chloral hydrate-anesthetized rats. Intrastriatal infusion (20 min fraction) of the nitric oxide generators sodium nitroprusside (200 microM, 500 microM, or 1 mM) and 3-morpholinosydnonimine (1 mM) increased extracellular dopamine levels. The facilitatory effects of 3-morpholinosydnonimine and potassium chloride on dopamine efflux were attenuated following pretreatment (100 min) and co-infusion of calcium free artificial cerebral spinal fluid containing magnesium chloride. Local potassium chloride infusion (100 mM) administered alone elevated striatal dopamine efflux to a similar degree as potassium chloride (100 mM) delivered 60 min after 3-morpholinosydnonimine infusion. These results demonstrate that like potassium chloride, nitric oxide facilitates striatal dopamine efflux in vivo via a mechanism largely dependent on extracellular calcium. Also, as intrastriatal potassium chloride infusion evoked similar increases in extracellular dopamine levels in controls and subjects receiving pretreatment with the NO-generator 3-morpholinosydnonimine, it is unlikely that the functional integrity of DA nerve terminals is compromised via a neurotoxic disruption of plasma membrane potential following enhanced striatal NO production.

Regulation of neurotransmitter release by endogenous nitric oxide in striatal slices

This study sought to determine the potential role of nitric oxide (NO) in N-methyl-D-aspartate (NMDA)-stimulated efflux of [14C] gamma-aminobutyric acid (GABA) and [3H]acetylcholine from striatal slices in vitro. In Mg2+-free buffer, NMDA-stimulated [14C]GABA and [3H]acetylcholine release were inhibited by the guanylate cyclase inhibitor, 1 H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), and, to a lesser extent, by the nitric oxide synthase inhibitor, nitroarginine (N-Arg). Since reversal of catecholamine transporters previously has been implicated in the mechanism underlying NO-induced catecholamine release, we used the GABA transport inhibitor, 1-(2-(((diphenylmethylene)imino)oxy)ethyl)-1,2,5,6-tetrahydro-3-py ridine-carboxylic acid hydrochloride (NNC-711), to address the role of GABA transport in NArg-sensitive NMDA-induced release. NNC-711 inhibited NMDA-stimulated [14C]GABA efflux by 50%, confirming our previous report that NMDA-stimulated GABA release is partially dependent on reversal of the transporter. The effect of N-Arg in the presence of NNC-711 was similar to its effect in the absence of the transport inhibitor, suggesting that reversal of the transporter is not involved in the NO component of NMDA-stimulated [14C]GABA release. These data suggest that glutamatergic transmission through striatal NMDA receptors is partially mediated through activation of the NO/guanylate cyclase pathway and that this mechanism may contribute to the tetrodotoxin sensitivity of NMDA-induced release of GABA and acetylcholine in the striatum.

Synaptic effects of nitric oxide on enkephalinergic, GABAergic, and glutamatergic networks of the rat periaqueductal gray

Previous studies have shown that the injection of nitric oxide (NO) donating compounds into the dorsal periaqueductal gray region of the midbrain (PAG) decreases mean arterial pressure (MAP), while the injection of NO synthase (NOS) inhibitors increases MAP. In this study we used both in-vivo and in-vitro preparations and examined the effect of a NO donor and a NOS inhibitor on MAP, membrane properties, and synaptic activities in PAG neurons. We found that: (1) Injection of the NO donor hydroxylamine (HA) into the dorsal PAG decreased MAP, while the injection of the neuronal NOS (nNOS) inhibitor, 1-(2-trifluoromethylphenyl) imidazole (TRIM) increased MAP. These responses were consistent and site-specific. (2) HA-evoked hypotensive responses were mediated by PAG neuronal activity, because they were blocked by pre-injection with gamma-amino-butyric acid (GABA). (3) HA consistently increased the rate of observable synaptic events while TRIM consistently decreased the rate of observable synaptic events. (4) Bicuculline (BIC) and naloxone (NAL) blocked HA-evoked increases in the rate of observable inhibitory synaptic events. (5) Perfusion with sodium nitroprusside (SNP) and illumination with bright light consistently elevated rates of observable synaptic events, and SNP-evoked increases of excitatory synaptic events were blocked by pretreatment with glutamic acid antagonists. (6) PAG-medullary projecting neurons exhibited similar response patterns. The results of this study suggest that: (1) NO production within the PAG is a major component of PAG-mediated cardiovascular responses. (2) The effects of NO may be mediated in part by increased presynaptic vesicular release of glutamic acid, GABA, and enkephalin.

Role of brain nitric oxide in (+/-)3,4-methylenedioxymethamphetamine (MDMA)-induced neurotoxicity in rats

The role of nitric oxide (NO) in the long-term serotoninergic neurotoxicity induced by (+/-)3,4-methylenedioxymethamphetamine (MDMA) in rats was investigiated. Pretreatment with Nomega-nitro-L-arginine (L-NOARG) (10 mg kg-1), a nitric oxide synthase (NOS) inhibitor, partially protected against long-term serotonin (5-HT) depletion induced by MDMA (40 mg kg-1) in frontal cortex and parietal cortex, but not in other brain regions examined. Brain NOS activities in these two regions were significantly elevated at 6 h after MDMA administration. Moreover, L-NOARG pretreatment caused significant inhibition of brain NOS activity but did not affect the acute 5-HT and dopamine (DA) changes or the hyperthermia induced by MDMA. These results suggest that it is the NOS inhibitory properties of L-NOARG, rather than its effects on the acute monoamine changes or the hyperthermia induced by MDMA, that are responsible for the prevention of neurotoxicity. The regional differences on the protection of L-NOARG and on the activation of NOS by MDMA indicate the unequal role that NO may play in MDMA-induced neurotoxicity in different brain regions.

Facilitation of striatal acetylcholine release by dopamine D1 receptor stimulation: involvement of enhanced nitric oxide production via neurokinin-2 receptor activation

The regulation of striatal cholinergic function by dopamine D1 receptor activation was examined in vivo in urethane-anaesthetized rats with microdialysis probes. Extracellular acetylcholine levels were enhanced by activation of D1 receptors either directly by a striatal application of the D1 receptor agonist (+)-SKF-38393 (3 microM) or indirectly by the release of dopamine evoked by striatal application of neurotensin (0.1 microM) under D2 receptor blockade. SR 144190, a new potent and selective non-peptide neurokinin-2 receptor antagonist (0.03-1 mg/kg, i.p.), dose-dependently reduced the acetylcholine release induced by (+)-SKF-38393 or neurotensin. Furthermore, intrastriatal application of SR 144190 (1 nM) blocked the increase in acetylcholine release induced by the local application of (+)-SKF-38393 (3 microM), neurokinin A (1 microM) or substance P (1 microM). Finally, a role for nitric oxide in mediating the effects of D1 neurokinin-2 receptor activation on acetylcholine release is proposed since local infusion of the competitive inhibitor of nitric oxide synthase, N(G)-monomethyl-L-arginine (0.01-10 microM), blocked the increase in acetylcholine release induced by (+)-SKF-38393 (3 microM), neurotensin (0.1 microM) or neurokinin A (1 microM) without affecting the enhancing effect of the neurokinin-1 agonist septide (0.1 microM).

Alterations in dopamine release but not dopamine autoreceptor function in dopamine D3 receptor mutant mice

Dopamine (DA) autoreceptors expressed along the somatodendritic extent of midbrain DA neurons modulate impulse activity, whereas those expressed at DA nerve terminals regulate both DA synthesis and release. Considerable evidence has indicated that these DA autoreceptors are of the D2 subtype of DA receptors. However, many pharmacological studies have suggested an autoreceptor role for the DA D3 receptor. This possibility was tested with mice lacking the D3 receptor as a result of gene targeting. The basal firing rates of DA neurons within both the substantia nigra and ventral tegmental area were not different in D3 receptor mutant and wild-type mice. The putative D3 receptor-selective agonist R(+)-trans-3,4,4a, 10b-tetrahydro-4-propyl-2H,5H-(1)benzopyrano(4,3-b)-1,4-oxazin+ ++-9-ol (PD 128907) was equipotent at inhibiting the activity of both populations of midbrain DA neurons in the two groups of mice. In the gamma-butyrolactone (GBL) model of DA autoreceptor function, mutant and wild-type mice were identical with respect to striatal DA synthesis and its suppression by PD 128907. In vivo microdialysis studies of DA release in ventral striatum revealed higher basal levels of extracellular DA in mutant mice but similar inhibitory effects of PD 128907 in mutant and wild-type mice. These results suggest that the effects of PD 128907 on dopamine cell function reflect stimulation of D2 as opposed to D3 receptors. Although D3 receptors do not seem to be significantly involved in DA autoreceptor function, they may participate in postsynaptically activated short-loop feedback modulation of DA release.

The role of the nitric oxide (NO) pathway in the discriminative stimuli of amphetamine and cocaine

To examine the role of the nitric oxide (NO) pathway in the stimulus effects induced by some psychostimulants, separate groups of rats were trained to discriminate between amphetamine (AMPH; 0.5 mg/kg) and saline, or cocaine (COC; 5 mg/kg) and saline using a standard two-lever operant procedure. Substitution studies showed that AMPH and COC generalized for the training drugs in a dose-dependent manner, their ED50, values being 0.1 mg/kg and 1.2 mg/kg, respectively. The dose-response function of both those psychostimulants did not change in the course of the experiment. Moreover, AMPH and COC induced cross-substitution effects towards each other. Successive combination tests demonstrated that injection of a fixed dose of the NO synthase (NOS) inhibitor 7-nitro indazole (7-NI; 25 mg/kg) plus different doses of AMPH or COC resulted in a leftward shift in the dose-response curves of those psychostimulants and a decrease in their ED50 values. On the other hand, pretreatment with the NO donor molsidomine (MOL), injected in a fixed dose of 100 mg/kg before AMPH and COC, shifted the dose-response curves of the psychostimulants to the right and increased their ED50 values. Our results indicate that NO plays an inhibitory role in the dopamine (DA)-evoked discrimination effects of AMPH and COC in rats.

Effect of nitric oxide donors on endogenous dopamine release from rat striatal slices. I: Requirement to antioxidants in the medium

Sodium nitroprusside (SNP) significantly decreased basal dopamine (DA) release when rat striatal slices were incubated in a physiological medium deficient in antioxidants. Depolarization-induced DA release (KCl 25 mM), which was accompanied with a 85% decline in tissue DA levels, was also inhibited by SNP and hydroxylamine (HA). Contrary to these findings, SNP did not protect the slices against depolarization-induced DA depletion. With HA, moreover, tissue DA levels were found to be depleted more than the control levels, indicating that DA, which is released from or stored in the slices, might be converted to an undetectable product under these conditions. Supporting this conclusion, incubation of the DA standards with SNP caused a dose-dependent loss in DA levels, an effect that was reversed partially by oxyhemoglobin and inhibited completely by antioxidants. Consistently, both SNP and HA, but not L-arginine, significantly increased basal DA release when striatal slices were incubated in antioxidants-containing medium. These results indicate that nitric oxide (NO), which is generated from SNP and HA by different mechanisms, stimulates DA release from rat striatal slices. Observation of this effect, however, requires the presence of antioxidants in the medium.

Effect of nitric oxide donors on endogenous dopamine release from rat striatal slices. II: The role of voltage-dependent sodium channels, calcium channel activation, reverse transport mechanism, guanylate cyclase and endogenous glutamate

Incubation of striatal slices with sodium nitroprusside (SNP) or hydroxylamine (HA) for 60 min caused a dose-dependent increase in dopamine (DA) release. This effect was inhibited completely by tetrodotoxin (TTX) (1 microM) if low concentrations of SNP (1 microM) or HA (10 and 100 microM) were tested. Although-higher concentration of SNP (10 and 100 microM) and HA (500 microM) were still effective in stimulating DA release, increases observed under these conditions were less than the values found in the absence of TTX. Verapamil (10 microM), but not omega-conotoxin (100 nM), significantly reduced DA release stimulated by high concentrations of SNP or HA. When verapamil was combined with TTX, moreover, SNP and HA failed to stimulate DA release. If striatal slices were incubated in the presence of nomifensine (10 microM), SNP and HA did not enhance DA release. SNP and HA-induced depletions in tissue DA levels were also protected by nomifensine. Inhibition of guanylate cyclase with 10 microM of methylene blue could not reduce the effects of NO-donors. SNP and HA also failed to alter endogenous glutamate release from striatal slices. Similarly, SNP and HA-induced increases in DA release were not affected by kynurenic acid and MK-801. These results indicate that NO-donors SNP and HA stimulate DA release by facilitating reverse DA transport. This effect seems to be dependent on the activation of both voltage dependent sodium channels and L-type of calcium channels. Results presented here also indicate that neither endogenous glutamate nor guanylate cyclase activation plays an intermediary role in stimulatory effects of NO-donors on DA release from rat striatal slices.

Castration decreases extracellular, but increases intracellular, dopamine in medial preoptic area of male rats

Dopamine (DA) is released in the medial preoptic area (MPOA) of male rats in the presence of a female, and it facilities male sexual behavior. Castration blocks the DA response to a female and the male's ability to copulate. The present experiments examined the effects of castration on (1) basal levels of extracellular DA in the MPOA, using the no net flux microdialysis technique, (2) the response of extracellular DA to amphetamine, and (3) tissue levels of DA. Castrated rats had lower basal levels of extracellular DA in the MPOA, compared with gonadally intact rats; in vivo recovery, a measure of uptake, was not different. This suggests that castration decreases DA release in basal conditions, as well as in response to a female. However, systemic amphetamine injections, which induce DA release, resulted in greater DA release in castrates. Finally, tissue levels of DA were higher in the MPOA, the caudate-putamen and the bed nucleus of stria terminalis of castrates. These data suggest that DA synthesis and storage in the MPOA are normal, or even enhanced, in castrates, and uptake is not altered. The deficit in extracellular levels appears to be related to release, perhaps due to decreased nitric oxide.

L-arginine produces NO-independent increases in dopamine efflux in rat striatum

The effect of L-arginine (L-ARG; 10-100 mM) on dopamine efflux from rat striatum was investigated using in vivo microdialysis. L-ARG (50 mM-100 mM), but not D-arginine (100 mM) nor L-citrulline (100 mM), produced a biphasic effect on dopamine efflux with an initial small reduction, followed by a large sustained increase. The effect of L-ARG was not prevented by nitric oxide synthase inhibition with NG-nitro-L-arginine methyl ester or 7-nitroindazole monosodium salt. Efflux of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) was reduced by L-ARG (10-100 mM), D-arginine (100 mM) and L-citrulline (100 mM). These data suggest that changes in dopamine, DOPAC and HVA efflux produced by high concentrations of L-ARG occur independently of NO, and that the use of high L-ARG concentrations are inappropriate when investigating the role of NO in striatum.

Endogenous nitric oxide facilitates striatal dopamine and glutamate efflux in vivo: role of ionotropic glutamate receptor-dependent mechanisms

We have investigated the influence of the nitric oxide synthase (NOS) substrate, NG-hydroxy-L-arginine (H-ARG) on dopamine (DA) and glutamate (GLU) efflux in vivo using concentric microdialysis probes implanted in the anterior-medial striatum of chloral hydrate-anesthetized rats. Intrastriatal infusion of H-ARG (100 microM, 200 microM, or 1 mM for 120 min) increased DA efflux in a dose-dependent fashion. The facilitatory effect of H-ARG (1 mM) on DA efflux was abolished following pretreatment (80 min) with the constitutive NOS inhibitor 7-nitroindazole (7-NI, 10 microM) but unaffected by L-NG(1-iminoethyl) lysine (100 microM) infusion. As both H-ARG (1 mM) and the NO-generator (+/-)-S-nitroso-N-acetylpenicillamine (1 mM) were observed to increase GLU efflux concurrently with the effect on DA efflux, we evaluated the potential intermediary role of GLU in NO-facilitated DA efflux using ionotropic GLU receptor antagonists. Local infusion of dizocilpine maleate (10 microM) or (+/-)-2-amino-3-[3-(carboxymethoxy)-5-methyl-isoxazol-4-yl] propionic acid (100 microM), attenuated the H-ARG (1 mM)-induced elevation of extracellular DA levels. Conversely, similar treatment with the kainate receptor antagonist d-gamma-glutamyl-aminomethanesulfonic acid did not alter H-ARG-induced DA efflux. To evaluate the regulatory influence of striatal NO on NMDA receptor activation, NMDA (100 microM) was co-perfused with either H-ARG (2 mM) or 7-NI (10 microM). While co-perfusion with 7-NI potentiated NMDA-induced DA efflux, similar treatment with H-ARG (2 mM) abolished the effect. These results demonstrate that endogenous NO production, stimulated via H-ARG-dependent activation of type 1 NOS, enhances striatal DA efflux via an increase in glutamatergic tone on ionotropic GLU-receptors. At higher levels of NOS activation (following H-ARG (2 mM) or NMDA infusion), NO may block glutamatergic neurotransmission via inhibition of NMDA receptor function.

Blockade of nitric oxide-evoked smooth muscle contractions by an inhibitor of guanylyl cyclase

Nitric oxide-induced contractile responses of smooth muscle were studied in vitro in guinea-pig small intestine. Application of nitric oxide (NO; 0.3-30 microM) evoked a small initial relaxation followed by a marked contractile response in plexus-containing longitudinal smooth muscle preparations from small intestine. The extent of the NO-evoked contractile response was dose-dependent and the response was blocked by tetrodotoxin. Atropine significantly reduced the NO-evoked contraction and the remaining part was abolished by the NK1-receptor antagonist CP 96,345. An inhibitor of soluble guanylyl cyclase, ODQ (1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one), abolished the NO-evoked contractile response. The results suggest that NO, in addition to the classical direct smooth muscle relaxing effect, causes activation of excitatory neurones, via a pathway utilizing soluble guanylyl cyclase, which leads to a smooth muscle contraction.

Voltametric assessment of brain nitric oxide during heatstroke in rats

Anesthetized rats exposed to a high ambient temperature develop heatstroke with brain ischemia. Since nitric oxide (NO) plays an important role during normothermic ischemia, its cortical and cerebellar production were continuously assessed in pentobarbital anesthetized rats exposed to heat by using differential pulsed voltammetry. After 60 min at thermoneutrality, the rats were submitted to an ambient temperature of 40 degrees C until death. After 60 min in the heat, the rats were injected intraperitoneally with saline, MK801 (1 mg.kg(-1)), an antagonist of N-methyl-D-aspartate (NMDA) receptors, or L-arginine p-nitroanilide (L-ANA; 100 mg.kg(-1)), an inhibitor of NO synthase. Just before death, a 70% increase in NO production was observed in both the cerebellum and the cortex of saline-treated rats. The cortical increase in NO was not modified by MK801 while the NO signal was suppressed by L-ANA.

Morphine- and anandamide-stimulated nitric oxide production inhibits presynaptic dopamine release

Morphine and anandamide stimulate the release of nitric oxide (NO) in diverse tissues. The present study examines the consequences of this action on neurotransmitter release in ganglia from two invertebrates: ventral chain ganglia from the leech Hirudo medicinalis and the pedal ganglion from the mussel Mytilus edulis. In these ganglia, preloaded serotonin (5-HT) and dopamine (DA) can be released by 50 mM KCl. Anandamide, an endogenous cannabinoid substance, suppresses the potassium-stimulated release of [3H]DA (80%), but not 5-HT, in a concentration-dependent manner, from the neural tissues of both. The effect of anandamide can be antagonized by pre-exposing the neural tissues of both animals to SR 141716A, a potent cannabinoid receptor antagonist. Prior treatment of the ganglia with N-omega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, significantly diminishes the inhibitory effect of anandamide. Morphine also inhibits [3H]DA release in a naloxone- and L-NAME-sensitive manner. Anandamide and morphine act through separate mechanisms since the respective antagonists show no cross-reactivity. The NO donor, SNAP, depressed the potassium-stimulated release of preloaded [3H]DA, but not 5-HT, in the neural tissues of both animals. D-Ala2-Met5 enkephalinamide (DAMA) also inhibited the potassium-stimulated release of [3H]DA in a naloxone-sensitive process. However, the effect of DAMA was seen in the presence of L-NAME (10(-4) M), indicating that the opioid peptide inhibition of the presynaptic release of DA is not coupled to NO. We postulate that cannabinoids and their endogenous effectors play a prominent role in the regulation of catecholamine release in invertebrates via NO release as is the case for opiate alkaloids.

Effects of modulation of nitric oxide on acoustic startle responding and prepulse inhibition in rats

The nitric oxide-arginine pathway is intimately connected to the release of dopamine and glutamate, two neurotransmitter systems that may be dysfunctional in schizophrenia. In addition, nitric oxide synthase inhibitors share several behavioral effects with the psychotomimetic drug, phencyclidine. Previous research has found that phencyclidine-like drugs disrupt prepulse inhibition of the acoustic startle response, an animal model of sensorimotor gating, an attentional process that is disrupted in certain neuropsychiatric disorders in humans (e.g., acute schizophrenia). The purpose of the present study was to examine the effects of nitric oxide modulators in this model. Following injection with a nitric oxide modulator or phencyclidine, rats were placed in startle chambers in which they were exposed to acoustic pulses presented alone or preceded by a prepulse. As in previous reports, phencyclidine disrupted prepulse inhibition at doses that did not affect startle during pulse alone trials. In contrast, the nitric oxide synthase inhibitors, N(G)-nitro-L-arginine (L-NOARG) and N(G)-nitro-L-arginine methyl ester (L-NAME), dose-dependently decreased startle during pulse alone trials, but neither drug affected prepulse inhibition. A nitric oxide precursor, L-arginine, produced similar results. Sodium nitroprusside (a nitric oxide releaser) and 7-nitroindazole (a third nitric oxide synthase inhibitor) did not affect startle amplitudes during pulse alone or prepulse + pulse trials. The present results suggest that modulation of nitric oxide synthesis or availability does not disrupt sensorimotor gating of the acoustic startle response and is probably not involved in mediation of this type of attentional deficit in humans.

Effects of nitric oxide on the horizontal cell network and dopamine release in the carp retina

In the teleost retina the intercellular messenger nitric oxide can be synthesized by several cell types including cone photoreceptors and H1 horizontal cells, indicating a modulatory role within the outer plexiform layer, the first stage of the visual information processing. Therefore, the aim of this study was to elucidate the effects of nitric oxide on the physiology of cone horizontal cells in the intact retina. The nitric oxide donor sodium nitroprusside (0.5-2.5 mM) enhanced the light responsiveness of cone horizontal cells and reduced the degree of electrical coupling in the network. Furthermore, the spread of intracellularly injected Lucifer Yellow was restricted. The effects on light responsiveness and electrical coupling were qualitatively mimicked by 8-bromo-cGMP (0.5 mM) and could not be achieved by ferrocyanide (1 mM), the byproduct of nitric oxide liberation from nitroprusside. The effects of NO on the responsiveness of horizontal cells may be due to an action on green- and red-sensitive cones. Nitroprusside (0.1 mM) diminished the K(+)-stimulated release of endogenous dopamine by 50%, whereas the basal dopamine release was not affected, indicating that the effects on electrotonic horizontal cell coupling were not elicited by an NO-induced release of dopamine. With respect to the morphologic plasticity of the cone-horizontal cell synapse the inhibitor of endogenous nitric oxide synthesis L-nitroarginine (0.1 mM) had no influence on the formation or retraction of spinules. These results show that NO affects the responsiveness and coupling of the horizontal cell network in a dopamine-independent way.

Release of [3H]dopamine from striatal and cerebral cortical slices from rats with thioacetamide-induced hepatic encephalopathy: different responses to stimulation by potassium ions and agonists of ionotropic glutamate receptors

The effects of depolarizing stimuli; high (50 mM) potassium ions and the glutamate receptor agonists N-methyl-D-aspartate, kainate and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) on the release of newly-loaded [3H]dopamine were studied in frontal cortical and striatal slices from control rats and from rats with acute hepatic encephalopathy induced with a hepatotoxin, thioacetamide. Hepatic encephalopathy enhanced the stimulatory effect of potassium ions by 20% in striatal slices and by 34% in frontal cortical slices. In striatal slices the stimulatory effects of N-methyl-D-aspartate and kainate were depressed in hepatic encephalopathy by 46% and 21%, respectively, which may be taken to reflect impaired modulation of striatal dopamine release by glutamate acting at N-methyl-D-aspartate or kainate receptors. In frontal cortical slices, the stimulatory effect of kainate was enhanced by 35% in hepatic encephalopathy but N-methyl-D-aspartate-stimulated release was not affected. The release evoked by 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate was not affected in hepatic encephalopathy in either brain region. Stimulation of dopamine release in the frontal cortex by depolarization or glutamate acting at kainate receptors could inhibit the activity of descending corticostriatal glutamatergic pathways, further impairing regulation of dopamine release by glutamate in the striatum.

Upregulation of (+)-7-hydroxy-N,N-di-n-[3H]propyl-2-aminotetralin binding following intracerebroventricular administration of a nitric oxide generator

Nitric oxide modulation of dopamine D2 and D3 receptor binding was examined using [125I]epidepride (D2) and (+)7-hydroxy-N,N-di-n-[3H]propyl-2-aminotetralin ([3H](+)-7-OH-DPAT, D3). Nitric oxide, generated by i.c.v. injection of S-nitroso-N-acetyl-penicillamine (SNAP; 5 microg or 10 microg), significantly increased the density of [3H](+)-7-OH-DPAT binding sites (39% and 134%, respectively) in the striatum 24 hours post-injection in the absence of Gpp(NH)p, representing an upregulation of either D3 receptors or high affinity D2 receptors. In the presence of 10 microM Gpp(NH)p, D3 receptor upregulation was maintained in both the 5 microg (increased 35%) and 10 microg SNAP (increased 44%) groups. [3H](+)-7-OH-DPAT binding was reduced in both striatum and nucleus accumbens in the presence of 10 microM Gpp(NH)p compared to binding in the absence of Gpp(NH)p, suggesting an upregulation of D3 receptors. Administration of SNAP did not alter total specific [125I]epidepride binding in either brain region. These data suggest that; 1) D3 receptor density is modified following nitric oxide generation, and 2) the density of high affinity D2 receptors identified by [3H](+)-7-OH-DPAT increases in the striatum, but decreases in the nucleus accumbens.

Nitric oxide promotes medial preoptic dopamine release during male rat copulation

Dopamine (DA) is released in the medial preoptic area (MPOA) of male rats during copulation. DA agonists infused into the MPOA facilitate, and antagonists impair, copulatory behavior. Local administration of the nitric oxide (NO) precursor L-arginine also increases DA release in the MPOA. The present experiment used microdialysis to test whether NO promotes DA release during copulation. Males received either an NO synthesis inhibitor, nitro-L-arginine methyl ester (L-NAME, 400 microM), or its inactive isomer D-NAME (400 microM) into the MPOA via a microdialysis probe for 3 h prior to the introduction of a female. Following D-NAME administration, DA increased during copulation, while L-NAME prevented this increase. NO may therefore promote DA release in the MPOA of male rats, thereby facilitating copulation.

Properties of 3,4-diaminopyridine-evoked dopamine and acetylcholine release in rabbit caudate nucleus slices: involvement of facilitatory adenosine A2 receptors or nitric oxide?

The 3H-overflow from slices of the rabbit caudate nucleus preincubated with tritiated dopamine (DA), or choline, and then superfused and stimulated twice with 3,4-diaminopyridine (3,4-DAP; 25 microM, 1 min), was explored as an in vitro model for evoked release of DA, or acetylcholine (ACh), respectively. In both cases the 3,4-DAP-evoked 3H-overflow was tetrodotoxin-sensitive and Ca(2+)-dependent and hence most probably represents action potential-induced exocytotic release of DA or ACh, respectively. Using pairs of preferential agonists/antagonists it was shown, that evoked DA release was inhibited via presynaptic D2 autoreceptors (quinpirole/domperidone) and kappa-opioid receptors (U-50488H/norbinaltorphimine). No evidence was found for the presence of presynaptic adenosine A1 or A2 receptors on dopaminergic terminals. Moreover, 3,4-DAP-evoked DA release was unaffected by increased intracellular cyclic AMP levels or by drugs affecting the NO/guanylate cyclase pathway. In a similar manner it was shown that 3,4-DAP-evoked ACh release was inhibited via presynaptic muscarine autoreceptors (oxotremorine/atropine) and dopamine D2 heteroreceptors (quinpirole/domperidone). Again, no evidence for the involvement of the NO/guanylate cyclase system in the modulation of ACh release was found, whereas the presence of inhibitory adenosine A1 receptors, but not of facilitatory A2 receptors, could be clearly established. It is concluded, that 3,4-DAP-evoked 3H-overflow from rabbit caudate nucleus slices preincubated with [3H]DA or [3H]choline, represents a simple and useful in vitro model for action potential-induced DA or ACh release, respectively. Moreover, at least in this model or rabbit brain region, facilitatory adenosine A2 receptors and the NO/guanylate cyclase system seem not to be involved in the release of these transmitters.

Fibroblast growth factor decreases locomotor activity in rats

The spontaneous locomotor behavior of rats receiving subcutaneous administration of either acidic or basic fibroblast growth factors was recorded in an activity cage. We report that doses between 1 and 100 micrograms/kg significantly decreased the horizontal and vertical activity, as well as the exploratory and stereotypy behavior of the rats. These effects of fibroblast growth factors seem to be specific since (i) they were cancelled by protein hydrolysis and anti-fibroblast growth factor antibodies, (ii) they were unrelated to their hypotensive activity and (iii) they were not attributable to their high structural similarity with the cytokine interleukin-1. Thus fibroblast growth factors did not show any thermogenic activity, did not affect the hypothalamic output of corticotropin-releasing factor and did not change the plasma levels of corticosterone. Pretreatment of the rats with a specific inhibitor of brain nitric oxide synthase prevented the effects of fibroblast growth factors, suggesting the involvement of nitric oxide in these behavioral modifications. Our results contribute to the accumulating evidence describing non-mitogenic activities of fibroblast growth factors.

Effects of nitric oxide on stimulated release of norepinephrine from female rat hypothalamic slices

Norepinephrine (NE) is an important neurotransmitter involved in ovarian steroid hormone regulation of female reproductive function in rats. Nitric oxide (NO) has also been suggested to be an essential mediator of gonadotropin-releasing hormone release and of lordosis behavior of female rats. These studies used a superfusion system to investigate the hypothesis that NO regulates [3H]NE release in the preoptic area (POA) and hypothalamus (HYP), brain regions that mediate ovarian steroid effects on reproductive function. The NO synthase inhibitors N-nitro-L-arginine and NG-nitro-L-arginine methyl ester did not modify either basal or N-methyl-D-aspartate (NMDA)-stimulated NE release in either brain region of ovariectomized, hormone-treated or control animals. The NO precursor L-arginine (L-Arg) reduced NMDA-stimulated NE release in POA but had no effect on KCl- or electrically-stimulated release. L-Arg did not influence basal or evoked release of [3H]NE from HYP slices. Sodium nitroprusside (SNP), a NO-generating compound, blocked the release of NE in response to NMDA stimulation but not in response to KCl or electrical stimulation. Thus, SNP is probably reducing NE release by acting as an NMDA antagonist rather than via NO production. There was a tendency for administration of both estrogen and progesterone to ovariectomized females to facilitate NMDA-stimulated NE release, particularly in the POA. Our data suggest that NO does not mediate basal or NMDA-stimulated NE release in rat POA and HYP. Therefore, NO regulation of lordosis behavior and gonadotropin release in female rats is probably not exerted at the level of NE release.

Intricate regulation of nitric oxide synthesis in neurons

There is little doubt that nitric oxide (NO) is one of the most important second messengers yet to be discovered, particularly in relation to its diverse roles in the regulation of neuronal function. As expected, synthesis of such a multifunctional molecule has to be under very tight control. For example, there is evidence that the rate of production of NO in neurons is regulated by several second messengers and their related protein kinases. NO by itself is also able to elicit negative feedback on the activity NO synthase (NOS) to attenuate its own rate of synthesis. Furthermore, NO modulates the release of neurotransmitters and alters the sensitivity of receptors that are coupled to stimulation of its synthesis. In healthy neurons, all of these intricate mechanisms are expected to cross-talk in harmony to result in the generation of optimal amounts of NO.

Nitric oxide influences dopaminergic processes

Nitric oxide, in recent years, has emerged as an important substance capable of modifying many biological processes. It is involved with both neural and immune processes. In my laboratory I will be examining the relationship of nitric oxide and its involvement with modifying dopaminergic processes. In this review, I examine reports that already document this relationship. Nitric oxide appears to be able to facilitate the release of various monoamines, especially dopamine. Furthermore, this gas has the ability to block the presynaptic re-uptake of dopamine as well. Taken together, it would appear that nitric oxide can prolong the "life' of dopamine in the synapse. Given the significance of dopamine in motor and psychological processes the significance of nitric oxide involvement increases exponentially.

Attenuation of cocaine kindling by 7-nitroindazole, an inhibitor of brain nitric oxide synthase

Recent studies suggest the involvement of the N-methyl-D-aspartate (NMDA) type of glutamate receptors and nitric oxide synthase (NOS) in the process of increased sensitivity to the convulsive effect of cocaine ("cocaine kindling"). The present study was undertaken to analyze the various behavioral stages in the development of cocaine kindling and to investigate the effect of 7-nitroindazole (7-NI), a relatively selective inhibitor of the neuronal NOS isoform, on the induction and expression of sensitization to the convulsive effect of cocaine. Also, the effect of 7-NI on responses produced by acute systemic administration of cocaine or N-methyl-D,L-aspartate (NMDLA) was investigated. Cocaine kindling was assessed on a five-stage scale following the administration of a sub-convulsant dose of the drug (35 mg/kg/day; i.p.) to Swiss Webster mice for 10 days. Stage 5 seizures developed following the 9th day of cocaine administration. Pre-treatment with 7-NI (25 mg/kg/day; i.p.) 15 min before cocaine for 10 days completely prevented the appearance of stage 4 and 5 seizures, and it significantly attenuated stage 3 behavior in response to a challenge cocaine dose (35 mg/kg) given either 24 hr or 10 days after 7-NI/cocaine administration was stopped. A single injection of 7-NI (25 mg/kg; i.p.) completely prevented the expression of cocaine kindled seizures. Whereas 7-NI had no effect on the responses elicited by acute cocaine administration (60 mg/kg; i.p.), this agent partially attenuated the effects induced by systemic administration of the NMDA receptor agonist NMDLA (250 mg/kg; i.p.). The present study indicates that 7-NI attenuates both the induction and expression of sensitization to the convulsive effect of cocaine. The findings that 7-NI attenuated cocaine kindling and partially blocked the effects produced by activation of the NMDA receptor, but not the effects induced by acute cocaine administration, support the role of the NMDA receptor and brain NOS in the development of cocaine kindling rather than in the acute effects of the drug.

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 of NG-nitro-L-arginine, a nitric oxide (NO) synthase inhibitor, on N-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 mM D-(-)-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 mM NG-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.

Nitric oxide regulation of methamphetamine-induced dopamine release in caudate/putamen

A possible role for NO modulation of dopamine (DA) release in the caudate/putamen (CPU) during methamphetamine (METH) exposure was investigated using in vivo microdialysis in rats. Inclusion of the nitric oxide synthase (NOS) inhibitors NG-nitro-L-arginine (NOARG), NG-nitro-L-arginine methyl ester (L-NAME) or D-NAME (less potent inhibitor) in the microdialysis buffer prior to METH minimally affected basal levels of DA, DOPAC or HVA in CPU microdialysate. However, L-NAME and NOARG produced concentration-dependent decreases of up to 64% (100 microM) in CPU DA levels in microdialysate during exposure to four doses of METH (5 mg/kg i.p./2 h), with lesser effects on DOPAC or HVA. Reversal of the NOARG inhibition was produced by inclusion of 500 microM of either L-arginine or L-citrulline in the microdialysate. D-NAME (100 microM) minimally affected levels of DA or metabolites. Paradoxically, inclusion of from 20 to 2 microM of the NOx generators isosorbide dinitrate (ISON) or sodium nitroprusside (SNP) in the microdialysis buffer decreased DA and DOPAC levels in microdialysate during METH exposure. This paradox might result from the concentrations of NOx produced by SNP or ISON being great and not regionally specific resulting in inhibition of DA release and/or synthesis while the NO generated endogenously during METH exposure may have localized and site-specific actions. Alternatively, NOx may inhibit NOS or other enzymes in the NO synthesis pathway, thereby reducing levels of an intermediate (other than NO) which potentiates DA release. In their entirety, our results indicate that NO generation in the CPU may augment the release of DA during METH exposure.

3,4-Diaminopyridine-evoked noradrenaline release in rat hippocampal slices: facilitation by endogenous or exogenous nitric oxide

The involvement of nitric oxide (NO) in the evoked release of noradrenaline (NA) was studied in rat hippocampal slices preincubated with [3H]NA and stimulated with 3,4-diaminopyridine (3,4-DAP; 200 microM) for 2 min. The 3,4-DAP-evoked [3H]overflow was enhanced by the NO synthase substrate L-arginine, but not by D-arginine; it was reduced by the NO synthase inhibitor NG-nitro-L-arginine, which also antagonized the effects of L-arginine. The corresponding nitro derivative of D-arginine was inactive and unable to block the effects of L-arginine. Also drugs known to produce NO in-vitro, like sodium nitroprusside (SNP), 3-morpholino-sydnonimine (SIN-1) and S-nitroso-N-acetylpenicillamine (SNAP) enhanced the 3,4-DAP-evoked NA release. The NO scavenger hemoglobin showed no significant effects when given alone, but reduced or abolished, respectively, the facilitatory effects of SNP, or SNAP and L-arginine. The cyclic GMP derivatives 8-Br-cGMP and Sp-8-p-chlorophenylthioguanosine-3',5'-cyclic monophosphorothioate (Sp-8-pCPT-cGMPS) also acted facilitatory, whereas the corresponding Rp-enantiomer of the latter compound was inactive, but antagonized the effect of Sp-8-pCPT-cGMPS. NA release evoked by 3,4-DAP (10 microM) from rat hippocampus synaptosomes was not affected by L-arginine or NG-nitro-L-arginine but slightly increased by SNAP and Sp-8-pCPT-cGMPS. Antagonists at NMDA, non-NMDA and metabotropic glutamate receptors neither affected the 3,4-DAP-evoked NA release nor the facilitatory effect of L-arginine.(ABSTRACT TRUNCATED AT 250 WORDS)

Cocaine kindling in mice. Responses to N-methyl-D,L-aspartate (NMDLA) and L-arginine

Previous studies proposed the involvement of the N-methyl-D-aspartate (NMDA) type of glutamate receptors in the development of sensitization to the convulsive effect of cocaine (cocaine kindling). The present study was undertaken to determine, first, if cocaine kindling is associated with enhanced sensitivity of the NMDA receptor to the convulsive response of N-methyl-D,L-aspartate (NMDLA), and second, whether in vivo modulation of nitric oxide synthase (NOS) function regulates the development of cocaine kindling. The following results were observed: 1. Cocaine-kindled animals were significantly more susceptible to the convulsive effect of the NMDA receptor agonist NMDLA than saline controls; 2. Pretreatment with the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 100 mg/kg; ip) blocked the development of cocaine kindling; 3. The protective effect of L-NAME was partially reversed with the coadministration of the NOS substrate, L-arginine (300 mg/kg; ip), but not D-arginine; and 4. L-Arginine (300 mg/kg; ip), but not D-arginine, amplified the development of cocaine kindling. Taken together, these findings suggest that supersensitivity of the NMDA receptor and activation of NOS may underlie the development of cocaine kindling.

Decreased spontaneous motor activity and startle response in nitric oxide synthase inhibitor-treated rats

In the central nervous system, nitric oxide has been proposed to be a retrograde messenger mediating learning and synaptic plasticity. Since only pretraining injections of nitric oxide synthesis inhibitors were shown to impair learning, we examined the possibility that systemic administration of these inhibitors might influence some non-specific aspects related to the organism's general psychophysiological status. Intraperitoneal administration of NG-nitro-L-arginine methyl ester (30 or 100 mg/kg) 60 min pre-test to adult rats resulted in: (i) altered exploratory pattern and reduced locomotion in a novel environment; (ii) reduced startle response to either acoustic or electric stimuli; and (iii) cardiovascular alterations. In addition, intracerebroventricular administration of N-nitro-L-arginine (10 microliters of a 10 mM solution) diminished the acoustic startle response. Specificity of these effects through nitric oxide was supported by the ability of the nitric oxide precursor, L-arginine, to prevent the inhibitors actions. These findings indicate that nitric oxide inhibitors interfere with the general psychophysiological status of the organism.

Modulation of striatal dopamine release in cerebral ischemia by L-arginine

The effect of L-arginine, the precursor of nitric oxide, on ischemic dopamine release from the striatum was investigated in Mongolian gerbils subjected to bilateral carotid artery occlusion (15 min) alone or with reflow (2 h). Dopamine and its metabolites were measured in the striatal extracellular space dialysate after continuous perfusion (2 microliters/min) of artificial extracellular fluid in the presence or absence of 15 mmol/liter L- or D-arginine or 1 mmol/liter nitro-L-arginine. L-Arginine but not D-arginine increased the striatal content of dopamine in pre- and postischemia whereas it lowered the levels of dopamine and 3-methoxytyramine induced by ischemia. In contrast, nitro-L-arginine reduced the preischemic levels of dopamine and 3,4-dihydroxyphenyl-acetic acid, and had no effect on the ischemic release of dopamine. These findings indicate that L-arginine stereospecifically modified the ischemic release and metabolism of dopamine. The data also suggest that the basal level of nitric oxide is not involved in dopamine release during ischemia but may participate in regulating dopamine release under physiological conditions.

Nitric oxide synthase in the hypothalamo-pituitary pathways

Several histochemical and physiological studies in the literature suggest that nitric oxide (NO) is involved in the posterior pituitary regulation. This study was set out to demonstrate the distribution of the pituitary projecting nitric oxide containing hypothalamic pathways. The fluorescent retrograde tracer fluorogold (FG) was injected into the pituitary gland in order to reveal the hypothalamic nuclei projecting to the pituitary gland. Nitric oxide synthase (NOS) was subsequently visualized from the same sections by NADPH-diaphorase histochemistry. More than 70% of the FG labelled neurons in the preoptic area, paraventricular, supraoptic, retrochiasmatic, anterior commissural and circular nuclei as well as in many other small neurosecretory centers in the hypothalamus contained also NADPH-diaphorase activity (NADPH-DA). In addition, some of the neurons in the periventricular nucleus as well as occasional neurons in the lateral hypothalamus projecting to the pituitary gland contained NADPH-DA. The present results give the first systematic neuroanatomical description of the hypothalamic NO synthase containing neurons projecting into the pituitary gland. They indicate that the pituitary receives a widely distributed NO innervation, which originates mostly in the magnocellular neurosecretory hypothalamo-pituitary system. In addition, the finding that some presumably non-neurosecretory pituitary-projecting neurons contain NO as well suggests that NO might be a more widely used regulator of the posterior pituitary secretion than previously expected.

Nitric oxide synthase inhibitors block behavioral sensitization to methamphetamine in mice

Repeated administration of methamphetamine (1.0 mg/kg) once daily for 7 consecutive days resulted in an augmentation of the locomotor-activating effect of methamphetamine (0.5 mg/kg) challenged 72 h after the last injection. Administration of the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine (10 and 30 mg/kg), before daily methamphetamine injections dose dependently prevented the development of behavioral sensitization to subsequent methamphetamine challenge. The mice given another NO synthase inhibitor, NG-nitro-L-arginine methyl ester (100 mg/kg), before daily methamphetamine injections showed significantly less locomotor activity in response to 0.5 mg/kg methamphetamine challenge than the mice given daily methamphetamine alone. Such effects were not observed when the inactive isomer, NG-nitro-D-arginine methyl ester (100 mg/kg), was administered daily prior to methamphetamine. Both NO synthase inhibitors exerted the acute effect to reduce spontaneous and methamphetamine-stimulated locomotor activity, while neither spontaneous locomotion nor hyperlocomotion in response to 1.0 mg/kg methamphetamine was altered 72 h after repeated administration of NG-nitro-L-arginine (30 mg/kg) or NG-nitro-L-arginine methyl ester (100 mg/kg) alone once daily for 7 days. On the other hand, pretreatment with the NMDA receptor antagonist, MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate), at 0.2 mg/kg also suppressed the development of sensitization to the locomotor-activating effect of methamphetamine. These findings suggest that NO formation possibly mediated by NMDA receptors is involved in mechanisms underlying the development of behavioral sensitization to methamphetamine.

Comparative study of normotensive and hypertensive nitric oxide synthase inhibitors on morphine withdrawal syndrome in rats

The effects of the normotensive, mainly centrally active nitric oxide synthase (NOS) inhibitor 7-nitro indazole and the hypertensive drug NG-nitro-L-arginine, which blocks both the endothelial and the central NOS, have been examined on naloxone-precipitated withdrawal in morphine-dependent rats. Both drugs attenuated the same withdrawal signs (teeth-chattering, penile licking, diarrhoea, chewing, wet-dog shakes, grooming), while other signs remained unaffected (rearing, jumping, ptosis, rhinorrhoea, irritability on touch). These findings indicate that mainly central (but not endothelial) nitric oxide is involved in the expression of some opioid withdrawal symptoms.

Increased striatal dopamine efflux in vivo following inhibition of cerebral nitric oxide synthase by the novel monosodium salt of 7-nitro indazole

The role of nitric oxide (NO) in striatal dopamine release has been controversial. Most NO synthase inhibitors affect more than one isoform of the enzyme and exert vasoconstrictor effects which may also affect striatal dopamine function. We now report on the effect of a soluble monosodium salt of the selective brain NO synthase inhibitor 7-nitro indazole (7-NINA). Using 7-NINA the first study of selective inhibition of the brain isoform of NO synthase on dopamine efflux in rat striatum was undertaken by use of in vivo microdialysis. Perfusion with 7-NINA (1 mM) increased striatal dopamine efflux. The effect of 7-NINA was partially antagonized (67%) by co-perfusion with L-arginine (1 mM), the precursor of NO formation in vivo. This suggests that 7-NINA induces a competitive inhibition of NO synthase activity. These data show that endogenous NO has an inhibitory effect on striatal dopamine efflux in vivo.

Role of nitric oxide in modulating neurotransmitter release from rat striatum

The effect of the nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) on the basal and stimulation-evoked release of dopamine (DA) and acetylcholine (ACh) was investigated in rat striatum. The experiments were carried out in isolated superfused striatal slices, loaded with either [3H]-dopamine or [3H]-choline. We have found that L-NAME reduced the electrical field stimulation-evoked release of DA, while its enantiomer N-nitro-D-arginine methyl ester (D-NAME) was ineffective. In the presence of the nitric oxide (NO) precursor L-arginine, L-NAME failed to influence DA release. Furthermore, treatment with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 completely reversed the effect of L-NAME on striatal DA release. In contrast, L-NAME had no effect on either the basal or the stimulation-evoked ACh release in any experimental conditions studied. Our data indicate that endogenously produced NO is involved in the modulation of striatal DA, but not in ACh release. Furthermore, it seems likely that the modulatory effect of NO is linked to activation of presynaptic NMDA receptors located on the striatal dopaminergic nerve terminals.

Effect of nitro-L-arginine on cerebral blood flow and monoamine metabolism during ischemia/reperfusion in the mongolian gerbil

Inhibition of nitric oxide synthase with nitro-L-arginine (i.p., 40 mg/kg body weight) in contrast to L-arginine (300 mg/kg body weight) delayed the initial recovery of cerebral blood flow (CBF) and altered dopamine (DA) metabolism in brain ischemia/reperfusion of Mongolian gerbils. Similar changes but more severe were observed with pargyline (monoamine oxidase inhibitor). Data suggest nitric oxide involvement in postischemic CBF recovery and modulation of DA metabolism due to nitro-L-arginine-induced CBF reduction.

Effects of gliosis on dopamine metabolism in rat striatum

Neuroimplantation is inevitably accompanied by gliosis. Although graft-induced trophic effects on host neurons may be mediated by glial cells, the effects of gliosis on dopamine (DA) metabolism remains unclear. To examine these effects, basic fibroblast growth factor (bFGF) was directly infused into the striatum of 12 male rats (250-280 g). One week later, substantial gliosis was demonstrated in the infused striatum by immunochemical staining for glial fibrillary acidic protein (GFAP) and quantified by GFAP Western blot analysis. One week after bFGF infusion, extracellular DA and its metabolites were measured by in vivo microdialysis using HPLC. Infusion of L-dopa through the dialysis probe resulted in a 60% reduction in the L-dopa-induced DA peak in the gliotic striatum compared with the normal side. After L-dopa infusion, dihydroxyphenylacetic acid (DOPAC) levels were similar between the gliotic and normal striatum. In contrast, homovanillic acid (HVA) levels were 26% higher in the gliotic striatum. Enzyme assays demonstrated that aromatic L-amino acid decarboxylase activity was unchanged in the gliotic striatum, but both MAO-A and MAO-B activities increased by 23% and 21%, respectively. These results suggest that the reduced striatal DA peak in the gliotic striatum after L-dopa administration was due to accelerated DA catabolism through enhanced MAO activity. The bFGF-induced striatal gliosis may serve as a model to study neurotransmitter metabolism in the gliotic brain caused by disease processes, aging, or tissue grafting.

Differential effects of nitric oxide gas and nitric oxide donors on depolarization-induced release of [3H]norepinephrine from rat hippocampal slices

The NO-generating compounds sodium nitroprusside (NP), nitroglycerin (NTG), and isosorbide dinitrate (ISDN) all significantly inhibited N-methyl-D-aspartate (NMDA)-stimulated release of tritiated norepinephrine ([3H]NA) from preloaded hippocampal slices of adult male Sprague-Dawley rats with IC50's of 114 microM, 1.2 mM, and 1.7 mM respectively. NTG and ISDN also inhibited KCl-stimulated release, while NP had no significant effect on KCl-stimulated release. Although these results suggest that the inhibitory effects of these compounds were mediated by release of NO, NTG and ISDN did not generate detectable levels of NO, and iron-cyanide complexes similar in structure to NP but lacking NO also inhibited release. In contrast, both S-nitroso-N-acetyl-D,L-penicillamine (SNAP) and authentic NO gas significantly enhanced NMDA-stimulated release of [3H]NA (EC50's: 331 and 3.4 microM respectively). This enhancement was not selective for NMDA-stimulated release, since both SNAP and NO potentiated KCl-stimulated release as well. In addition, NO gas significantly enhanced NMDA-stimulated release of tritiated dopamine ([3H]DA) from striatal slices and [3H]NA from cortical and cerebellar slices. Analogs of cyclic guanosine monophosphate (cGMP) had no significant effect on NMDA-stimulated transmitter release, suggesting that the observed increase in release is via a cGMP-independent mechanism. While exogenous NO enhanced both NMDA- and KCl-stimulated neurotransmitter release, it appears that endogenous NO does not play a role in this depolarization-induced release since NO synthase inhibitors did not significantly reduce NMDA-stimulated [3H]NA release. The possibility remains that endogenous NO could modulate neurotransmitter release in other circumstances.

The effects of a photosensitive nitric oxide donor on basal and electrically-stimulated dopamine efflux from the rat striatum in vitro

The reported effects of nitric oxide (NO) on dopamine release from the striatum are variable and its precise effect on striatal nerve terminals is unclear. In the present study a novel method of applying NO to brain tissue in situ was employed. Photo-activation of Roussin's Black Salt (RBS), retained in isolated perfused brain tissue, was used to release NO at will upon illumination. Basal and electrically-stimulated dopamine efflux from the rat striatum in vitro was measured in real time using fast cyclic voltammetry. Illumination of an RBS pre-treated brain slice elicited a light intensity-related increase in basal dopamine efflux. Concomitantly there was a decrease in the level of electrically-stimulated dopamine efflux. Illumination in the absence of RBS pre-treatment had no effect on basal or stimulated dopamine efflux. The increase in basal dopamine efflux upon photo-activation of RBS was reduced by the presence of 10 microM oxyhaemoglobin, but was insensitive to the removal of extracellular calcium or the addition of 1 microM sulpiride. The decrease in electrically-stimulated dopamine efflux following illumination was not affected by the presence of either oxyhaemoglobin or sulpiride. It is concluded that NO, produced by photo-activation of RBS, releases dopamine from the rat striatum in vitro by a mechanism independent of extracellular calcium entry.