S81

CATECHOLAMINERGIC NEURONS PROJECTING FROM THE VENTROLATERAL MEDULLA OBLONGATA

TO THE PREOPTIC AND ANTERIOR HYPOTHALAMIC AREAS: THEIR NEURAL ACTIVITY AFTER

VARIOUS ENDOCRINOLOGICAL MANIPULATIONS

HIDETO KABA*, HIDEO SAITO and KATSUO SETO, Department of Physiology, Kochi

Medical School, Nankoku, Kochi 781-51

A total of 135 presumed AI noradrenergic (and/or CI adrenergic) neurons

projecting from the ventrolateral medulla oblongata to the preoptic and

anterior hypothalamic areas through the medial forebrain bundle was anti-

dromically activated in proestrous (P), dlestrous I (DI), ovariectomized

oil-treated (OVX + Oil) and ovariectomized estrogen-treated (OVX + E) rats

under urethane anesthesia. Both the frequency of successful antidromic

propagation into the somatodendritic spike and the mean spontaneous firing

rate were significantly lower in OVX + Oil rats than in P, DI or OVX + E

rats; but there was no significant difference among P, DI and OVX + E rats.

A statistical analysis of spontaneous activity of these neurons was also

carried out. Neither the distribution patterns of the interspike interval

histogram, nor serial correlation coefficients of interval sequence was

significantly different among these groups.

ELECTROPHYSIOLOGICAL PROPERTIES OF NEURONS IN THE AI AREA PROJECTING TO THE PARAVENTRICULAR NUCLEUS OF THE HYPOTHALAMUS IN RATS

HIROSHI KANNAN, HIROSHI YAMASHITA, TOSHIMASA OSAKA* and MASANORI KASAI , Department of Physiology, University of Occupational and Environmental Health, School of Medicine, i-i, Iseigaoka, Yahatanishiku, Kitakyushu 807, Japan.

Extracellular recordings were obtained from the region of the AI- noradrenergic cell group in the ventrolateral medulla in urethane-chloralose anesthetized rats. Stimulation of the paraventricular nucleus (PVN) of the hypothalamus evoked antidromic action potentials. On the basis of antidromic spike latencies, these neurons could be divided into two groups (mean~S.D., 7.8 ~ 3.0 ms, n=24 and 35.81 8.5 ms, n=47). Slow conducting cells showed irregular, slow spontaneous discharges; while almost all the fast conducting cells did not show spontaneous discharges. The spontaneous activity of slow conducting cells was suppressed by i.v. clonidine administration (9-27~g/Kg). The effects of clonidine could be blocked by administration of the ~ -

2 adrenoreceptor antagonist, yohimbine (0.48-0.8 mg/Kg). Baroreceptor activation induced by i.v. administration of phenylephrine inhibited ii of the 23 slow conducting cells tested. Similar elevation of blood pressure in baroreceptor- denervated rats was without effect. On the other hand, the responses by clonidine and yohimbine remained unimpaired in denervated rats. These physiological and pharmacological properties of slow conducting cells were similar to those previously reported for noradrenergic neurons in the locus coeruleus and A5 area. The results show the existence of two different populations among neurons in the A1 area which project directly to the PVN, and suggest that the presumed A1 noradrenergic neurons are involved in mediating afferent information from cardiovascular baroreceptors to the PVN.