H. Aradachi et al., MEDIAN PREOPTIC NEURONS PROJECTING TO THE SUPRAOPTIC NUCLEUS ARE SENSITIVE TO HEMODYNAMIC-CHANGES AS WELL AS TO RISE IN PLASMA OSMOLALITY IN RATS, Journal of neuroendocrinology, 8(1), 1996, pp. 35-43
Extracellular single unit activity was recorded from 73 neurones in th
e median preoptic nucleus (MnPO), identified by antidromic activation
as projecting to the supraoptic nucleus (SON) area in urethane-anaesth
etized male rats. Thirteen of 73 identified MnPO neurones were silent,
and 44 of 60 spontaneously active MnPO neurones were tested for their
responses to electrical stimulation of the nucleus tractus solitarius
(NTS). The cells were divided into 4 groups according to their respon
ses; those which were excited orthodromically (OD+; n=15), those which
were unresponsive (UN; n=21), those which were inhibited orthodromica
lly (OD-; n=4), those which showed initial inhibition followed by exci
tation (OD-+ n=4). Some of these neurones were further tested for thei
r responses to haemorrhage and/or increase in blood pressure produced
by intravenous administration of the alpha-agonist, phenylephrine, and
/or to hyperosmotic stimulation produced by intraperitoneal injection
of 1.5 M NaCl. Six out of 10 OD+ cells were excited by haemorrhage, 6
out of 11 OD+ cells were inhibited by phenylephrine, and 5 out of 9 OD
+ cells were excited by hypertonic saline. On the other hand the UN ce
lls tended to be unresponsive to each type of stimulus. Three out of 7
OD+ cells were excited by both haemorrhage and hypertonic saline, and
3 out of 8 OD+ cells were inhibited by phenylephrine and excited by h
ypertonic saline. The results may suggest that MnPO neurones which rec
eive afferent input from the NTS may be sensitive nor only to haemodyn
amic change but also to change in plasma osmotic pressure and that suc
h population of MnPO neurones may integrate a part of the haemodynamic
and osmotic information and contribute to the control of neurohypophy
sial hormone release.