Differential effects of stress on presynaptic and postsynaptic 5-hydroxytryptamine-1A receptors in the rat brain: An in vitro electrophysiological study

Extracellular and intracellular recording techniques were used to assess po ssible changes in the functional properties of 5-hydroxytryptamine-1A recep tors in brain slices prepared from rats subjected to different stress parad igms. Whereas a 30-min restraint stress did not alter the inhibitory influe nce of ipsapirone on the firing of serotoninergic neurons in the dorsal rap he nucleus, the same session followed by a 24-h isolation produced a signif icant decrease in the potency of the 5-hydroxytryptamine-1A agonist to inhi bit the electrical activity of these cells. Similarly, exposure of the anim als to novel uncontrolled environmental conditions for 16 h significantly r educed the potency of ipsapirone to decrease the firing rate of serotoniner gic neurons in brain stem slices. The effects of the latter two stressful p aradigms were observed in slices from intact rats, but not in those from ad renalectomized animals. Intracellular recording showed that exposure of the animals to novel uncontrolled environmental conditions markedly reduced th e potency of 5-carboxamidotryptamine to hyperpolarize serotoninergic neuron s in the dorsal raphe nucleus and to decrease the input resistance of their plasma membrane. In contrast, the same stressful paradigm exerted no signi ficant influence on the membrane effects of this 5-hydroxytryptamine-1A ago nist on pyramidal cells in the CA1 hippocampal area. These data show that, like the direct application of corticosterone on to b rain slices [Laaris N. et al. (1995) Neuropharmacology 34, 1201-1210], the stress-induced in vivo elevation of serum levels of endogenous corticostero ne is associated with desensitization of somatodendritic 5-hydroxytryptamin e-1A receptors in the dorsal raphe nucleus. The differential changes in 5-h ydroxytryptamine-1A receptor sensitivity due to stress in the latter area v ersus the hippocampus further support the idea that somatodendritic and pos tsynaptic 5-hydroxytryptamine-1A receptors are regulated differently in the rat brain. (C) 1999 IBRO. Published by Elsevier Science Ltd.