Effects of naloxone and naltrexone on the increased water intake and drinking duration in phenobarbitone-treated rats

Genetic, maternal, and heterosis effects on voluntary water consumption in mice

In standard laboratory conditions, inbred mouse strains with normal kidney function show a 4-fold range of daily water consumption. This study uses two strains of inbred mice identified as high and low consumers, their reciprocal F1 crosses, and inter se bred F2s. Daily consumption data were collected on 607 animals for 4 d during the 4th, 5th, and 6th wk using custom water bottles. Animals were weighed at the beginning of the 4th, 5th, 6th, and 7th wk. Consumption data were corrected for metabolic BW (Bwt0.67) prior to analysis, so units of water consumption are expressed in mL consumed per gram of Bwt0.67 per day. Variables BW and water consumption were fitted to a mixed model including the effects of sex, strain, and their interaction with sire within strain fitted as a random effect. Contrasts were designed to test the direct genetic, maternal genetic, individual heterosis, and maternal heterosis effects. An interaction (P < 0.0001) was observed between sex and strain so all analyses were conducted separately for each sex. C57Brown/CDJ animals (Brown) consumed more water than C57Black/10J animals (Black) (P < 0.0001). A maternal effect (P = 0.036, P = 0.029) was observed in males at the 4th and 5th wk as F1 animals with a Black dam (F1Black) consumed less than F1 animals with a Brown dam (F1Brown) males. No significant heterosis effect was observed for water consumption. For weight analysis, Black animals were significantly larger than Brown animals at 28 d (males P = 0.004, females P = 0.026), but no difference was observed the remainder of the trial. Further, F1Brown females were significantly smaller than F1Black females at 28 d (P < 0.0001) and F1Brown males tended to be smaller than F1Black males (P = 0.078). Animals from the reciprocal F1 crosses showed an increase in birth weight (P < 0.0001) over pure strains. These strains form the foundation stock of an experiment designed to isolate genes influencing water consumption by reciprocal backcrossing and selection.

Naloxone blocks the antianxiety but not the motor effects of benzodiazepines and pentobarbital: experimental studies and literature review

The role of opioid systems in the anticonflict effect of chlordiazepoxide, diazepam and pentobarbital was evaluated with a modified Vogel procedure. First, morphine, ineffective by itself, was combined with subeffective or marginally effective doses of the benzodiazepines in order to detect possible potentiation. However, the combined treatment reduced licking in the Vogel procedure as well as in a licking test where no shock was administered. Several doses of the benzodiazepines and pentobarbital were then administered in combination with several doses of the opiate antagonist naloxone. A dose-dependent inhibition of anticonflict effect was obtained. In an additional experiment, it was shown that naloxone blocked the effects of diazepam in the elevated plus-maze procedure. Motor deficiencies, as evaluated with a rotarod test, produced by the benzodiazepines and pentobarbital could not be antagonized by naloxone. It is concluded that opioids are important for the anticonflict but not for the motor effects of these drugs. An analysis of published studies concerning the interaction of opioids and benzodiazepines in several procedures supposed to reflect anxiolytic effects shows that the inhibition obtained with naloxone is reliable and not procedure specific. The mechanisms by which opiate antagonists produce this inhibition of anticonflict activity are not known. It is tentatively suggested that opioid activation associated with stress may be a necessary component of anxiolysis.

Effects of naloxone and picrotoxin on diazepam- or pentobarbital-induced hyperphagia in nondeprived rats

Diazepam and pentobarbital administered intravenously increased food intake in a dose-dependent manner in nondeprived rats. Low doses of naloxone inhibited diazepam-induced feeding, but did not inhibit pentobarbital-induced feeding. On the other hand, picrotoxin inhibited feeding induced by both drugs. These findings suggest that diazepam-induced hyperphagia is related to endogenous opioid mechanisms, but pentobarbital-induced hyperphagia is not. Hyperphagia induced by both drugs may be related to GABAergic neurons.

Methadone, pentobarbital, pimozide and ethanol-intake

For 28 days, water-deprived rats were given a daily, 1-hr opportunity to take a sweetened ethanol solution (ES) or water. Across days under this regimen, rats gained weight normally and increased intake of ES until they were taking considerable amounts. Across the next 13 days of the regimen, selected groups were given, before the opportunity to drink, one of five doses of methadone (from 0.5 to 8.0 mg/kg), pentobarbital (from 5 to 30 mg/kg), or their vehicles. Large doses of both agents increased intakes, with methadone (1 and 2 mg/kg) increasing only ES-intake. Subsequently, while the daily regimen continued, rats were given pimozide (0.2, 0.4, or 0.6 mg/kg) at either 1 or 4 hr before the opportunity to drink. Pimozide did not reduce ES-intake. Next, they were given a dose of pentobarbital (5.0 mg/kg) with challenge doses of naloxone (0.3, 1.0, 3.0 mg/kg). Naloxone dose-relatedly antagonized pentobarbital's potential to increase intakes.

Pentobarbital-induced drinking does not rely on a renal dipsogen

Injections of pentobarbital have been shown to produce drinking in both deprived and nondeprived rats and a number of other studies have shown that pentobarbital is a potent renin releasor. Since renin has been shown to be involved in thirst regulatory mechanisms and since the dipsogenic actions of other renin-releasing agents have been blocked by nephrectomy, we sought to determine whether or not pentobarbital-induced drinking relies on a renal dipsogen. Rats were either "sham" operated or nephrectomized under ether anesthesia. Five to six hours later, animals in each group were injected with either 9.5 mg/kg pentobarbital sodium or vehicle, and intakes were measured 60 minutes later. Statistical analysis of water intakes indicated that pentobarbital produced significant drinking in both control operated and in nephrectomized rats, and that the intakes in these two groups did not differ. These results indicate that pentobarbital-induced drinking is not secondary to increased plasma renin activity and may suggest the involvement of central mechanisms in the drinking response.

Endogenous opiates: 1983

This paper is the sixth in an annual series of reviews of research involving the endogenous opiates, each installment being restricted to work published during the previous year. Although the early articles in the series attempted to be comprehensive and cover the complete range of research with the opiate peptides, in the last two years we have limited our coverage to non-analgesic and behavioral work due to the enormous number of articles published in the field. The specific areas discussed here include stress, tolerance and dependence, consummatory responses, other gastrointestinal functions, interactions with alcohol, mental illness, learning and memory, cardiovascular responses, respiratory effects, thermoregulation, neurological disorders, activity, and miscellaneous other topics. As in previous years, we have attempted to present a relatively complete review of the subjects covered only for the previous year and generally have not tried to evaluate their contributions relative to those of past years.

Enhancement of osmotic- and hypovolemic-induced drinking by chlordiazepoxide in rats is blocked by naltrexone

Recent reports indicate that benzodiazepine-induced hyperphagia can be antagonised by naloxone, an opiate antagonist. Benzodiazepines are also known to facilitate water ingestion in water-deprived rats, and the present study showed that in addition, benzodiazepine treatment can enhance drinking which is elicited by an osmotic thirst stimulus (2 M hypertonic saline) or by a hypovolemic thirst stimulus (20% polyethylene glycol). In both cases, low dose levels of naltrexone (also an opiate antagonist) dose-dependently suppressed the facilitation of thirst-aroused drinking by chlordiazepoxide. Taken with recent biochemical data these behavioral results indicate that the enhancement of ingestive responses by benzodiazepines may depend upon a naloxone-reversible release of endogenous opioid peptides.