The role of adrenal or testicular hormones in voluntary ethanol and NaCl intake of crowded and individually housed rats

Impaired Fluid Intake, but Not Sodium Appetite, in Aged Rats Is Mediated by the Cyclooxygenase-Prostaglandin E2 Pathway

Aging results in decreased fluid intake following dehydration and other dipsogenic stimuli; similar reductions in sodium intake have also been observed with aging. Given that cyclooxygenase (COX)-derived prostanoids are elevated in aged rats in the midbrain and proinflammatory prostanoids are known to decrease fluid intake in dehydrated rats, the aim of this study was to determine if the reductions of fluid intake and sodium intake in aging are mediated by proinflammatory eicosanoid signaling. Therefore, we examined the effect of acute COX inhibition in adult (4 months-old) and aged (30 months-old) rats prior to ingestive behavior challenges. COX inhibition, using acetylsalicylic acid (ASA), increased fluid intake in aged, but not adult, rats in response to 24-h dehydration. ASA had no effect on salt intake following sodium depletion and ASA did not change basal fluid or sodium consumption in either age group. Hypothalamic COX-1 and -2, prostaglandin E synthase (PGES) and inducible nitric oxide synthase (iNOS) mRNA expression were all elevated in aged animals, leading to elevated PGE₂ levels. COX expression in the hypothalamus was reduced by ASA treatment in rats of both ages resulting in reduced PGE₂ levels in aged ASA treated animals. These data indicate that the reduced fluid intake that occurs in aging is due to increased COX-PGE₂-mediated inflammation. However, the reduced sodium intake in these animals appears to occur via an alternate mechanism.

Social housing and alcohol drinking in male-female pairs of prairie voles (Microtus ochrogaster)

RATIONALE

Social environment influences alcohol consumption in humans; however, animal models have only begun to address biological underpinnings of these effects.

OBJECTIVES

We investigated whether social influences on alcohol drinking in the prairie vole are specific to the sex of the social partner.

METHODS

In Experiment 1, control, sham, and gonadectomized voles were placed either in mesh-divided housing with a same-sex sibling or isolation with access to ethanol. In Experiment 2, animals were given an elevated plus maze test (EPM) and then females were paired with a castrated male followed by isolation or mesh-divided housing with access to ethanol. In Experiment 3, subjects categorized as low or high drinkers based on initial ethanol intake were placed in mesh-divided housing with an opposite-sex partner of the same or opposite drinking group and ethanol access. Subjects were then moved back to isolation for a final ethanol access period.

RESULTS

Same-sex pairs showed social facilitation of drinking similar to previous reports. Gonadectomy did not affect alcohol drinking. Opposite-sex paired animals in Experiment 2 did not differ in alcohol drinking based on social housing. EPM measures suggested a relationship between anxiety-like behaviors and drinking that depended on social environment. Experiment 3 identified moderate changes in alcohol preference based on social housing, but these effects were influenced by the animal's own drinking behavior and were independent of their partner's drinking.

CONCLUSIONS

Social influences on alcohol self-administration in prairie voles differ based on the sex of a social partner, consistent with human drinking behavior.

Evidence for suppressant effects of testosterone on sex-typical ethanol intake in male Sprague-Dawley rats

Previous studies have shown that adult female rats consume more ethanol than adult males. Castration of male rats has been found to increase their ethanol intake and preference to levels significantly elevated above their sham-gonadectomized counterparts and similar to levels observed in females. The purpose of the present experiment was to examine whether testosterone replacement in castrated adult male rats would be sufficient to restore the relatively low levels of ethanol drinking characteristic of intact adult male rats. Males were either gonadectomized and implanted with a testosterone propionate pellet (RPL), gonadectomized and implanted with a placebo pellet (GX), sham-gonadectomized and implanted with a placebo pellet (SH), or were left non-manipulated (NM). Voluntary ethanol intake was measured using a 2h limited-access drinking paradigm, with access to two bottles: one containing water, and the other a sweetened ethanol solution. Hormone replacement was sufficient to return ethanol intake and preference of castrates to levels comparable to both SH and NM control males. Ethanol preference of RPL males was also significantly suppressed compared to GX males by the end of the measurement period, whereas these group comparisons did not reach statistical significance for g/kg ethanol intake. These data suggest that testosterone serves to suppress ethanol preference in male rats, and may contribute to the sex differences in ethanol preference and consumption commonly reported in adult rats.

The effects of gonadectomy on age- and sex-typical patterns of ethanol consumption in Sprague-Dawley rats

BACKGROUND

Ethanol intake levels characteristic of adult males and females emerge postpubertally. The present set of experiments examined the consequences of prepubertal and adult gonadectomies to explore whether the presence of gonadal hormones at puberty exerts organizational influences and/or plays an activational role in age- and sex-typical patterns of ethanol consumption.

METHODS

Male and female Sprague-Dawley rats were gonadectomized (GX), received sham gonadectomy (SH), or were left nonmanipulated (NM) at 1 of 2 ages, either prepubertally on postnatal day (P) 23 (early) or postpubertally in adulthood on P70 (late). Early surgery animals were tested for ethanol consumption either during adolescence (P28 to 39) or in adulthood at the same age that late surgery animals were tested (P75 to 86). Voluntary ethanol consumption was indexed using a 2-hour limited-access paradigm, with access to 2 bottles: one containing water and the other a sweetened ethanol solution.

RESULTS

Age of GX did not impact patterns of ethanol consumption. Removal of testicular hormones in males, regardless of age of removal, elevated consumption levels in adulthood to female-typical levels. Ovariectomy did not have notable effects on ethanol drinking in females. Ethanol intake and preference of early SH males were significantly greater than those of both late SH and NM males. Removal of the gonads prior to puberty did not influence ethanol drinking or preference during adolescence in either males or females.

CONCLUSIONS

These results suggest that testicular hormones play an activational role in lowering ethanol intake and preference of adult male rats. Pubertal hormones, in contrast, were found to exert little influence on ethanol drinking or preference during adolescence, although the effect of surgical manipulation itself during development was found to exert a long-lasting facilitatory effect on ethanol consumption in adulthood.