Noradrenergic modulation of gonadotropin-inhibitory hormone gene expression in the brain of Japanese quail

Abstract

Gonadotropin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide that inhibits gonadotropin synthesis and release in birds and mammals. In Japanese quail, GnIH neurons express the noradrenergic receptor and receive noradrenergic innervation. Treatment with noradrenaline (NA) stimulates GnIH release from diencephalic tissue blocks in vitro. However, the effects of NA on hypothalamic GnIH gene expression have not been determined. We investigated noradrenergic regulation of GnIH gene expression in the brain of male quail using the selective noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4). We first showed that DSP-4 reduced the number of noradrenergic (dopamine-β-hydroxylase immunoreactive) cells in the locus coeruleus (LoC) and specifically lowered NA concentration in the hypothalamus of male quail. Other monoamines, such as dopamine and serotonin, were not affected by the drug treatment. DSP-4 did not decrease the numbers of noradrenergic cells of the lateral tegmental cell group or the plasma NA concentration. Decreased hypothalamic NA levels after DSP-4 treatment did not change GnIH gene expression in the brains of quail during their interaction with conspecifics. On the other hand, GnIH gene expression increased in the brains of quail socially isolated for 1 h after the DSP-4 treatment. These results suggest that some noradrenergic neurons have inhibitory effects on GnIH gene expression of the hypothalamus in solitary quail.

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