Conditioned release of 5-hydroxytryptamine in vivo in the nucleus accumbens following isolation-rearing in the rat.

This study examined the effect of isolation-rearing in the Lister hooded rat on extracellular 5-hydroxytryptamine in the medial nucleus accumbens following footshock and in relation to a conditioned emotional response. Inescapable mild footshock was associated with an immediate and prolonged increase in extracellular 5-hydroxytryptamine in the medial nucleus accumbens of isolation-reared rats. In group-reared rats (footshock-treated) and control groups (no footshock) there was no significant change in extracellular 5-hydroxytryptamine levels. When exposed to the contextual stimulus 140 min later (testing box without shock) there was an immediate and long-lasting increase in extracellular 5-hydroxytryptamine in the nucleus accumbens of the isolation-reared rats, however, the contextual stimulus did not significantly affect extracellular 5-hydroxytryptamine in the medial nucleus accumbens of group-reared rats. The results show that exposure to footshock and conditioning to context are not normally associated with a change in extracellular 5-hydroxytryptamine in the medial nucleus accumbens, however, in rats exposed to social isolation from weaning, both stimuli increase extracellular 5-hydroxytryptamine. The isolation-induced increase in presynaptic serotonergic function in the medial nucleus accumbens contrasts with previous reports of reduced 5-hydroxytryptamine release in the hippocampus and therefore suggests that isolation-rearing differentially affects the function of serotonergic neurons in the brain. The changes in 5-hydroxytryptamine function in the medial nucleus accumbens may represent physiological adaptations to stress or may occur secondary to changes in the function of another neurotransmitter, possibly dopamine.