VASOPRESSIN NEURON ACTIVATION AND FOS EXPRESSION BY STIMULATION OF THE CAUDAL VENTROLATERAL MEDULLA

The present study demonstrates that projections ascending from the cau dal ventrolateral medulla have direct effects on the expression of the immediate early gene c-fos and of the arginine-vasopressin gene in ne urosecretory cells of the hypothalamic supraoptic nucleus, Intense Fos -like immunoreactivity (Fos-LI) was observed in many magnocellular neu rons of the supraoptic nucleus after electrical stimulation of the cau dal ventrolateral medulla, In sham-operated rats, Fos-LI was absent or present in very few magnocellular neurons in the supraoptic nucleus, Fos-LI was visible in neurons expressing arginine-vasopressin, and was seen rarely in oxytocin neurons by double-immunostaining method. This study showed that 76% of all Fos-positive cells were arginine-vasopre ssin immunoreactive, whereas only 4% of them showed oxytocin immunorea ctivity in the supraoptic nucleus, With in situ hybridization, a high level of arginine-vasopressin mRNA was noted in the supraoptic nucleus 3 h after stimulation of the caudal ventrolateral medulla; the expres sion was highest 6 h after the stimulation compared with the same regi on in sham-operated animals, These findings suggest that noradrenaline , released from the axon terminals originating from the caudal ventrol ateral medulla, may participate in the regulation of gene transcriptio n of arginine-vasopressin in response to physiological stimuli. (C) 19 97 Elsevier Science Inc.