Blockade of alcohol-induced locomotor sensitization and conditioned place preference in DBA mice by 7-nitroindazole

Nitric oxide mediation of morphine-induced place preference in the nucleus accumbens of rat

In the present study, the effects of intra-nucleus accumbens injection of L-arginine, a nitric oxide (NO) precursor, and N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, on morphine-induced conditioned place preference in male Wistar rats were investigated. Our data showed that subcutaneous (s.c.) injection of morphine sulphate (0.5-10 mg/kg) significantly increased the time spent in the drug-paired compartment in a dose-dependent manner. Intra-accumbens administration of L-arginine (0.03 and 0.05 microg/rat) with an ineffective dose of morphine (0.5 mg/kg) elicited significant conditioned place preference, while intra-accumbens administration of L-NAME (0.3, 0.1 and 1 microg/rat) decreased the acquisition of conditioned place preference induced by morphine (7.5 mg/kg). The response to different doses of L-arginine was decreased by L-NAME (0.03 microg/rat). L-Arginine and L-NAME by themselves did not elicit any effect on place conditioning. Intra-accumbens administration of L-arginine but not L-NAME significantly decreased the expression of morphine (7.5 mg/kg)-induced place preference. The attenuation of already established morphine-induced place preference on the test day by L-arginine was inhibited by L-NAME. The results indicate that NO may be involved in the acquisition and expression of morphine-induced place preference.

Injection timing determines whether intragastric ethanol produces conditioned place preference or aversion in mice

Previous studies have shown that mice develop conditioned place preference (CPP) when ethanol is administered by intraperitoneal (ip) or intravenous (iv) injection. The present studies examined CPP in mice using the intragastric (ig) route of administration. Inbred mice were surgically implanted with chronic intragastric cannulae and exposed to an unbiased place conditioning procedure in which infusion of ethanol (2 or 4 g/kg) was paired with a conditioned stimulus (CS+). A different CS was paired with water. In Experiments 1-2, ethanol was infused just before exposure to CS+. Contrary to previous studies involving intraperitoneal injection, infusion of 4 g/kg ig ethanol produced a significant conditioned place aversion (CPA). However, when a 5-min delay was inserted between infusion and CS exposure (Experiments 3-4), the same dose produced CPP. These outcomes are not consistent with expectations derived from a recent study in selectively bred rats, suggesting that sensitivity to ethanol reward is enhanced by intragastric administration. However, the finding that intragastric ethanol can produce either CPP or CPA depending on dose and injection timing is consistent with previous intraperitoneal ethanol studies in mice. Although the parameters differ for each route of administration, it appears that the same underlying processes can be invoked to explain how manipulation of injection timing affects the direction of ethanol-induced place conditioning. More specifically, in both cases, CPA can be attributed to an initial, short-lived aversive effect, whereas CPP can be attributed to a delayed rewarding effect of ethanol.

Repeated administration of gamma-hydroxybutyric acid (GHB) to mice: assessment of the sedative and rewarding effects of GHB

Because of the sedative/hypnotic and euphoric effects of gamma-hydroxybutyric acid (GHB), the recreational use of the drug has increased significantly. In the current study we investigated the sedative and rewarding effects of GHB in Swiss Webster mice. Although the acute administration of GHB (200 mg/kg) caused marked hypolocomotion, repeated administration of the drug for 6 or 14 days produced tolerance to this effect. In addition, the administration of GHB 300 mg/kg to naive mice caused catalepsy, which dissipated in mice pre-exposed to GHB (200 mg/kg). Consequently, after repeated treatment with GHB, tolerance developed to both the hypolocomotion and cataleptic effects of the drug. The administration of GHB or its precursor gamma-butyrolactone for 14 days increased the striatal content of dopamine. The sedative effects of GHB may be due to hypodopaminergic activity from inhibition of dopamine release and a subsequent increase in the intraneuronal dopamine level. The rewarding effect of GHB was assessed in the conditioned place preference paradigm. Mice treated repeatedly with 250 mg/kg for 7 days developed conditioned preference for the GHB-paired compartment of the cage, suggesting that the GHB cue is rewarding. The development of tolerance to the sedative effects of GHB coupled with the rewarding properties of the drug support the abuse potential of GHB. Further studies are necessary to determine the mechanism underlying the development of tolerance to GHB and the rewarding effect of the drug.

Effect of the neuronal nitric oxide synthase inhibitor 7-nitroindazole on methylphenidate-induced hyperlocomotion in mice

The psychostimulant methylphenidate (MPD) is used for the treatment of attention-deficit/hyperactivity disorders (ADHD) in adolescents. In the present study we investigated the effect of repeated administration of a low (10 mg/kg) and a high (40 mg/kg) dose of MPD on the locomotor activity of Swiss Webster mice, and the influence of inhibition of the neuronal nitric oxide synthase (nNOS) on MPD-induced hyperlocomotion. In the first experiment, mice were administered either vehicle or the nNOS inhibitor 7-nitroindazole (7-NI; 25 mg/kg), prior to the administration of MPD (10 or 40 mg/kg), for five consecutive days; injections were paired with the test cage ('novel environment') on days 1 and 5. A challenge injection of MPD (10 or 40 mg/kg), given after a 10-day drug-free period, resulted in sensitization to the motor stimulating effect of the low dose of MPD but tolerance to the high dose of MPD. 7-NI blocked the induction of sensitization but had no effect on the development of tolerance. The place-dependent-hyperlocomotion (e.g. conditioning) that developed after the administration of either the low or high dose of MPD was blocked by pretreatment with the nNOS inhibitor. In the second experiment, mice were administered MPD (10 or 40 mg/kg; 5 days) in their home cage and after a 10-day drug-free period were challenged with either vehicle/MPD or 7-NI/MPD. The low dose of MPD elicited a sensitized response that was blocked by the co-administration of 7-NI. The high dose of MPD produced neither sensitization nor tolerance; 7-NI did not affect the response to the high dose of MPD. These findings suggest: (a) MPD-induced sensitization and tolerance are dependent on the dose of the drug and the environment where the drug is delivered (home cage versus test cage); (b) context-dependent hyperlocomotion developed in the absence of a sensitized response to the drug; (c) nNOS is involved in the induction and expression of sensitization to MPD as well as in the conditioned locomotion produced by the drug; (d) no involvement of nNOS in the effects of a high dose of MPD was detected.

The effect of 7-nitroindazole on the acquisition and expression of D-methamphetamine-induced place preference in rats

The present study investigated the role of nitric oxide (NO) in the rewarding effects of D-methamphetamine using 7-nitroindazole, a potent inhibitor of neuronal nitric oxide synthase (nNOS), as determined by the conditioned place preference paradigm. Male Sprague-Dawley rats treated with D-methamphetamine (1 mg/kg) or saline every other day for 8 days (four drug and four saline sessions) developed marked place preference for the drug-paired side. The administration of 7-nitroindazole (12.5-50 mg/kg) 30 min prior to the exposure to D-methamphetamine dose-dependently attenuated the acquisition of D-methamphetamine-induced conditioned place preference. In addition, when it was acutely administered 30 min prior to the testing session of an already established D-methamphetamine-induced conditioned place preference, 7-nitroindazole (12.5-50 mg/kg) attenuated the expression of this conditioned response in a dose-dependent manner, while 7-nitroindazole (25 and 50 mg/kg) alone showed no place preference effects. These findings indicate that nitric oxide (NO) is involved in the rewarding properties of methamphetamine and suggest that selective nNOS inhibitors maybe useful in the management of methamphetamine abuse.

Effects of intracerebroventricular administration of 7-nitroindazole on tolerance to ethanol

Previous studies have shown that nitric oxide (NO) is involved in the development of rapid tolerance to the motor incoordination produced by ethanol. In order to further investigate this involvement, three experiments were undertaken using the tilt-plane and the hypothermia tests. The first demonstrated that 7-nitroindazole (7-NI), a preferential neuronal NO synthase (nNOS) inhibitor, injected by intracerebroventricular (i.c.v.) route, blocked the development of rapid tolerance to ethanol-induced motor incoordination. This effect was prevented by i.c.v. injection of L-arginine. The second experiment showed that D-arginine did not influence the blockade of tolerance produced by 7-NI. The third experiment revealed that i.c.v. injection of 7-NI also blocked the development of tolerance to the hypothermic effect of ethanol. These results support the hypothesis that nNOS-derived NO participates in the development of rapid tolerance to ethanol.

Nitric oxide and substance dependence

The free-radical gas nitric oxide (NO) plays an important role in a diverse range of physiological processes. It is synthesized from the precursor L-arginine by the enzyme NO synthase (NOS), which transforms L-arginine into NO and citrulline. This synthetic pathway exists in the central nervous system (CNS), and NO appears to be a messenger molecule in the CNS, fulfilling most of the criteria of a neurotransmitter. Recent studies indicate that NO may play an important role in dependence on drugs of abuse. The purpose of this review is to address the role of NO in dependence on substances such as opioids, ethanol, psychostimulants and nicotine. Inhibitors of NOS modulate withdrawal from opioids and ethanol, diminishing many signs of withdrawal. In addition, NOS inhibitors suppress signs of withdrawal from nicotine. These data suggest that NO may be involved in the expression of withdrawal signs, and they leave open the possibility that NO may mediate the development of many of these signs. Although preliminary, data to date suggest that glutamate neurotransmission may be related to these beneficial effects of NOS inhibitors on signs of withdrawal. Emerging data further suggest that NO may have a general role in the dependence potential of various classes of drugs of abuse. Thus, modulation of NO systems may be a potential therapeutic target for treatment of substance abuse.

Intracerebroventricular injection of antisense oligos to nNOS decreases rat ethanol intake

Nitric oxide (NO) has been implicated in alcohol drinking behavior using NO synthase (NOS) inhibitors that are nonselective of the different isoforms of NOS. In the brain, there are two constitutive isoforms of NOS, neuronal NOS (nNOS) and endothelial NOS (eNOS). We used an antisense oligodeoxynucleotide directed against nNOS in ethanol dependent male Wistar rats to examine the specific contribution of nNOS in the control of ethanol intake. Rats were subjected to a free-choice situation water/ethanol (10% v/v) after chronic ethanol intoxication by inhalation of ethanol vapor. During the free-choice situation, rats were twice daily for 4 days intracerebroventricularly injected with either saline, or end-capped phosphorothioate-protected antisense or mismatch oligodeoxynucleotide (25 microg/4 microl per injection), or acamprosate (1 mg/kg body weight) as reference product for its anticraving properties. Our results showed that the antisense treatment, but not the mismatch treatment, reduced both ethanol intake and ethanol preference during treatment and posttreatment periods (by 25-30%) without alteration of the body weight gain. The antisense treatment, but not the mismatch treatment, also down-regulated nNOS mRNA levels (by 30%) and NOS activity in the hippocampus. The anticraving drug, acamprosate reduced both ethanol intake (by 58%) and ethanol preference. All these results suggest that nNOS is involved in the regulation of alcohol dependence.