The role of social isolation in ethanol effects on the preweanling rat

Abstract

The present experiments investigated the effects of acute ethanol exposure on voluntary intake of 0.1% saccharin or water as well as behavioral and nociceptive reactivity in twelve–day-old (P12) rats exposed to differing levels of isolation. The effects of ethanol emerged only during short-term social isolation (STSI) with different patterns observed in males and females and in pups exposed to saccharin or water. The 0.5 g/kg ethanol dose selectively increased saccharin intake in females, decreased rearing activity in males and attenuated isolation-induced analgesia (IIA) in all water-exposed pups. Ingestion of saccharin decreased IIA, and the 0.5 g/kg ethanol dose further reduced IIA. The 1.0 g/kg ethanol dose, administered either intragastrically or intraparentionally, also decreased IIA in P12 females, but not in P9 pups. A significant correlation between voluntary saccharin intake and baseline nociceptive reactivity was revealed in saline injected animals, saccharin intake was inversely correlated with behavioral activation and latency of reaction to noxious heat after 0.5 g/kg ethanol in females. The 0.5 g/kg ethanol dose did not affect plasma corticosterone (CORT) measured 5 hours after maternal separation or 20 minutes after ethanol injection. Female pups CORT level was inversely correlated with magnitude of IIA that accompanied the first episode of STSI (pretest isolation) 1.5–2 hours before CORT measurement. The present findings suggest that the anxiolytic properties of ethanol are responsible for enhancement of saccharin intake during STSI. Furthermore, differential reactivity of P12 males and females to STSI plays an important role in ethanol effects observed at this age.

Central effects of ethanol interact with endogenous mu-opioid activity to control isolation-induced analgesia in maternally separated infant rats

“…First, subjects can become more sensitive to pain, in which case IIA would be expressed in values lower than zero. Second, mean values of relative time spent in rearing significantly below 10% have been observed in other conditions (socially non-deprived animals; - (Kozlov et al, 2012b)) Thus, from a technical point of view, we were capable of revealing still lower values of nociceptive reactivity than those shown in Figures 6. The fact that such changes were not detected in ethanol- and saccharin-exposed animals suggests that the low dose of ethanol and ingestion of saccharin blocked development of opioid-dependent IIA.…”

“…The fluid flow tracking technique was described in detail elsewhere (Kozlov et al, 2008; Kozlov et al, 2012b). This technique used a photocell system that tracked light through a translucent tube in terms of the border between filled and unfilled parts of the tube.…”

“…Because previous experiments (Kozlov et al, 2009, 2012b) indicated that effects of ethanol in P12 rat were sex-dependent, gender was included in all experimental designs. With three doses of i.c.…”

“…In infant rats exposure to ethanol can aggravate or ameliorate reactions to social isolation, with ethanol’s effects dependent on dose of ethanol, duration of social isolation, age of the animal and type of behavioral activity expressed during isolation (Arias et al, 2010; Kozlov et al, 2012b; Pautassi et al, 2012b). Recently we found that in 12-day old rat pups the effects of 0.5 g/kg ethanol on ingestion of a palatable fluid emerged only in pups separated from their littermates for 8 minutes (short-term social isolation, STSI) (Kozlov et al, 2012b). Low doses of ethanol ameliorated isolation-induced analgesia, but ethanol-mediated effects were age-dependent suggesting an association between developmental changes in stress reactivity and sensitivity to ethanol.…”

“…Recently we found that exposure to saccharin ameliorated, to some extent, the stress reaction to social isolation (Kozlov et al, 2012b). Given opioid involvement in modulation of palatability and the hedonic effects of sweet taste (Doyle et al, 1993; Berridge, 2000; Ferraro et al, 2002), we suggest an interaction between opioid–mediated changes in saccharin intake and expression of isolation-induced analgesia that also seems dependent on mu-opioid activity.…”