AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 6 1516-R1520, Copyright © 1990 by American Physiological Society
Noxious somatic stimuli excite neurosecretory vasopressin cells via A1 cell group
T. A. Day and J. R. Sibbald
Department of Physiology, University of Otago Medical School, Dunedin, New Zealand.
Activation of nociceptive somatic afferents excites hypothalamic
neurosecretory cells and stimulates the release of vasopressin. To
investigate the possibility that relevant afferent information is relayed
through the A1 norepinephrine cell group of the caudal ventrolateral
medulla, single-unit recording experiments were performed in pentobarbital
sodium-anesthetized rats. The effects of somatic nerve stimulation,
application of noxious somatic stimuli, and A1 region stimulation on the
activity of putative vasopressin-secreting neurosecretory cells of the
supraoptic nucleus were compared. The predominant effect of femoral and
sciatic nerve stimulation on these cells was excitation, 54% (n tested =
113) displaying a marked increase in discharge probability, which had a
mean onset latency of 72 +/- 3 ms and a mean duration of 114 +/- 9 ms.
Almost all cells (96%) responding to somatic nerve stimulation were also
excited by pinching of the ipsilateral or contralateral hindlimb paw, and
the majority (84%) displayed a matching but shorter latency response to A1
region stimulation (mean onset 35 +/- 4 ms, duration 55 +/- 9 ms). A1
region injections of the inhibitory neurotransmitter gamma-aminobutyric
acid reversibly blocked the effects of both somatic nerve stimulation (n =
14) and paw pinch (n = 9) on putative vasopressin cells. These results
indicate that excitation of vasopressinergic neurosecretory cells by
noxious somatic stimuli requires activation of neurons of the caudal
ventrolateral medulla and hence are consistent with the proposal of a role
for the A1 norepinephrine cell group.
