“Effect of the serotonergic blockade of lateral parabrachial nucleus on the activity induced by blood volume expansion in the hypothalamic vasopressinergic and oxytocinergic neurons”.

L. MARGATHO; L. VIVAS; A. GODINO; J. ANTUNES-RODRIGUES

Lisboa, Portugal

Congreso; XII Inernational Congress of Endocrinology; 2004

Effect of the serotonergic blockade of lateral parabrachial nucleus on the neuronal activity induced by blood volume expansion in the hypothalamic vasopressinergic and oxytocinergic neurons. Our previous evidences showed an increase in oxytocin (OT) and atrial natriuretic peptide secretion after blood volume expansion (BVE) while vasopressin (AVP) secretion is inhibited. They also indicate that injection of a serotoninergic antagonist, methysergide (MET), into the lateral parabrachial nucleus (LPBN) reduces electrolyte excretion and urine output induced by BVE.  Together, these results suggest that the serotoninergic system participates in the hydroelectrolyte response after BVE modulating the activity of oxytocinergic and vasopressinergic neurons. The Aim of the present work was to study the effect of LPBN injection of MET on the neuronal activity induced by BVE in the vasopressinergic and oxytocinergic cells of the paraventricular (Pa) and supraoptic nucleus (SON). Methods and Results: Male Wistar rats (250–300 g) with stainless steel cannulas implanted bilaterally into the LPBN and with a catheter inserted into the right external jugular vein and advanced to the right atrium were used. Blood volume was expanded by injection of isotonic saline (NaCl 0.15 M, 2 ml/100 g b.w.) over 1 min in rats. MET (4 mg/0.2 ml) or vehicle was injected into the LPBN bilaterally, 20 min before the BVE.  Ninety minutes after BVE, the rats were perfused for immunohistochemical detection of Fos-OT or Fos-AVP, along the Pa and SON. Our preliminary analysis indicates that in rats submitted to BVE, LPBN injection of MET increases the percentage of Fos-AVP immunoreactive neurons in the lateral magnocellular division of the Pa (PaLM, 169% increase vs. control) and in the SON (91% increase vs. control). On the other hand, LPBN injection of MET reduced the number of oxytocinergic neurons activated by BVE in the anterior commissural nucleus (AC, 40% decrease vs. control), in the PaLM (49% decrease vs.control), in the medial magnocellular division of the Pa (PaMM, 25% decrease vs.control) and in the SON (32% decrease vs. control). Along the other divisions of the Pa, the number of oxytocinergic or vasopressinergic activated neurons was not different between experimental and control groups. Conclusion: The present findings suggest that the sertonergic system participates of the central neural pathway that integrates inputs derived from BVE modulating the activity of oxytocinergic and vasopressinergic neurons of the Pa and SON. SUPPORTED BY: FAPESP, PRONEX, CNPq and CONICET. Se adjunta abstract a continuación ya que no se dispone de la versión Power Point