The direct effect of thyroliberin on nonapeptidergic cells of the supraoptic and paraventricular nuclei was studied on cultured rat hypothalamic slices. Incorporation of labeled thyroliberin into vasopressinergic and oxytocinergic cells and a decrease in functional activity of these cells were observed in both hypothalamic nuclei.
Key Words: thyroliberin; vasopressin; oxytocin; hypothalamus; paraventricular nucleus; supraoptic nucleusMost peptide hypothalamic hormones act as neurohormones affecting the target cells via blood and liquor and as neurotransmitters, i.e. affect other nerve cells (including those producing neurohormones) via the corresponding synapses [7]. There is evidence on the presence of corticoliberinergic synapses of cells of the paraventricular hypothalamic nucleus (PVN) that produce thyroliberin (TRH) [12]. Somatostatin-and somatoliberin-producing cells of the arcuate nucleus also interact via synaptic connections [11 ].The interaction between the cells producing releasing-hormones, in particular between TRH-cells and nonapeptidergic cells in the hypothalamic PVN and supraoptic nucleus (SON) remains unclear. The existence of such connections is confirmed by the thyreostimulating effect of vasopressin and oxytocin [2][3][4] and by the effect of TRH on the functional state of PVN and SON cells in vivo [1,9]. However, the data obtained in vivo provide little information on the mechanism of TRH action on nonapeptidergic cells. Our aim was to carry out a morphofunctional study of vasopressin-and oxytocinergic cells in isolated hypothalamic slices exposed to TRH.
MATERIALS AND METHODSThe study was carried out on mature male Wistar rats weighing 120-140 g kept under standard vivarium Laboratory-of Neuroendocrinology, I. M. Sechenov Institute of Evolution, Physiology, and Biochemistry, Russian Academy of Sciences, St. Petersbur 9 conditions. After decapitation, the brain was rapidly removed and 400-p slices contaimng SON and/or PVN were prepared from the hypothalamic area. The slices were preincubated in Earle's medium aerated with carbogen (95% 02+5% CO2) at 37~ Preincubation was performed in 3 portions of the growth medium (30 min in each portion).In the first experimental series we studied incorporation of 3H-TRH into neurosecretory cells of PVN and SON. After preincubation, the hypothalamic slices were transferred to the growth medium with 3H-TRH (1.75• 1.85x106 Bq/mol, NEN Product) and incubated for 15 and 30 min (the medium was changed every 15 min).The slices were fixed in picric acid and formalin (3:5) and processed by standard histological methods. Serial sections (6 p) were used in immunohistochemical PAP-reaction pertormed with nonlabeled antibodies to oxytocin. The sections were covered with an M-type photoemulsion (KhimFotoProekt, Moscow), exposed for 6 weeks, and developed in 2,4-diaminophenol dihydrochloride. Binding of 3H-TRH in PVN and SON cells was accesses by the number of silver grains concentrated above one cell (30 vasopressin-and 30 oxytocinergic cells for each rat). The number ...