Inhibition of drinking by naltrexone in the rat: interaction with the dopamine D-1 antagonist SCH 23390 and the D-2 antagonist sulpiride

Role of dopamine D1-like and D2-like receptors in the activation of ingestive behaviour in thirsty rats licking for water

RATIONALE

Analysis of lick pattern for sucrose and NaCl and of the forced swimming response after dopamine antagonist administration led us to suggest that dopamine on D₁-like receptors is involved in behavioural activation, and the level of activation is "reboosted" on the basis of an evaluation process involving D₂-like receptors. Although some studies investigated licking microstructure for water after dopamine antagonists, the within-session time course of their effect was never investigated.

OBJECTIVES

The aims of this study were to further investigate the role of dopamine receptors in the mechanisms governing water ingestion, focussing on the within-session time course of the microstructure parameters, and to test the proposed hypothesis.

MATERIALS AND METHODS

The effects of the dopamine D₁-like receptor antagonist SCH 23390 (0.01-0.04 mg/kg) and of the dopamine D₂-like receptor antagonist raclopride (0.025-0.25 mg/kg) on licking microstructure for water were examined in 20-h water-deprived rats in 30-min sessions.

RESULTS

As previously observed with sucrose and NaCl, SCH 23390 reduced licking by reducing burst number, suggesting reduced behavioural activation. Moreover, it resulted in an increased burst size. Raclopride reduced the size of licking bursts, while their number was either increased or decreased depending on the dose.

CONCLUSION

The results support the suggestion that D₁ receptors are involved in behavioural activation and D₂ receptors are involved in a related evaluation process. Within the framework of the proposed hypothesis, the increased burst size after D₁-like receptor blockade might be interpreted as a pro-hedonic effect consequent to the increased cost of the activation of the licking response.

Naloxone attenuates drinking behavior in psychiatric patients displaying self-induced water intoxication

1. The present study was performed to examine the effect of naloxone on drinking behavior in three schizophrenic inpatients with psychosis, intermittent hyponatremia, and polydipsia. 2. Their body weight were checked five times daily and the maximum weight gain during a day was chosen as an index of their polydipsia. 3. After control recording for six weeks, a daily naloxone (0.6 mg) injection series was performed once every two weeks for three series (six weeks). Withdrawal of this drug for six weeks resulted in weight gain recovering to control level. 4. The present study showed that naloxone seems to be a potential treatment for psychiatric patients displaying self-induced water intoxication and that endogenous opioid systems are involved in the compulsive drinking behavior of this syndrome.

Endogenous opiates: 1989

This paper is the twelfth installment of our annual review of the research published during 1989 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal functions; mental illness; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; locomotor activity; sex, development, pregnancy, and aging; immunological responses; and other behavior.