GABAergic projection from the arcuate nucleus to the supraoptic nucleus inthe rat

Electrical stimulation of the neurones in the hypothalamic arcuate nucleus results in a transient inhibition followed by a marked post-stimulus excita tion of magnocellular neurones Of the supraoptic nucleus. Microdialysis adm inistration of the gamma-aminobutyric acid agonist (GABA(A)), muscimol, dir ectly into the supraoptic nucleus inhibited both oxytocin and vasopressin n eurones and these actio ns were fully reversed by the GABA(A) antagonist bi cuculline, In addition, bicuculline administration blocked the inhibition i nduced by arcuate stimulation, but had no effect on the post-stimulus excit ation. Thus, part of the inhibitory pathway arising from or passing through the arcuate nucleus to the supraoptic nucleus is mediated by the neurotran smitter GABA, However, the post-inhibitory excitation induced by arcuate st imulation is not a rebound response, but appears to involve an independent excitatory pathway. (C) 2000 Elsevier Science Ireland Ltd. All rights reser ved.