ROLE OF THE HYPOTHALAMIC PARAVENTRICULAR NUCLEUS IN CARDIOVASCULAR REGULATION

1. The paraventricular hypothalamic nucleus (PVH) is a complex structu re with both neuroendocrine and autonomic functions, It is a major sou rce of vasopressin and the primary source of corticotropin-releasing f actor. In addition, parvicellular PVH neurons have reciprocal connecti ons with brainstem autonomic centres and directly innervate sympatheti c preganglionic neurons, Evidence is reviewed which indicates that in conscious rats PVH activation increases blood pressure, heart rate, re nal nerve activity and plasma renin activity, 2, In conscious rats, a non-hypotensive haemorrhage (13 mL/kg blood loss over 24 min) results in increased numbers of Fos-immunoreactive cell nuclei within both mag nocellular and parvicellular PVH neurons, including the ventral medial parvicellular regions known to contain neuronal projections to brains tem autonomic centres and spinal cord sympathetic preganglionic neuron s, 3, Cell-selective ibotenate lesions of the parvicellular PVH signif icantly blunt the corticosterone response but do not alter blood press ure, heart rate or plasma renin concentration response to non-hypotens ive or hypotensive haemorrhage. This and earlier studies indicate that , while the PVH is necessary for the corticosterone response and contr ibutes to increased vasopressin release during blood loss, it does not play an important role in the sympathetic nervous system and renin-an giotensin responses to hypovolaemia and hypotension, 4. There is evide nce to indicate that the parvicellular PVH serves as a necessary relay for cardiovascular and renin responses to certain behavioural stresso rs. We propose that cardiovascular information relayed to parvicellula r PVH autonomic regions may be used to modulate behavioural, rather th an homeostatic, effects on haemodynamics and renin release.