Electrophysiological and morphological properties of pre-autonomic neurones in the rat hypothalamic paraventricular nucleus

1. The cellular properties of pre-autonomie neurones in the hypothalamic pa raventricular nucleus (PVN) were characterized by combining in vivo retrogr ade tracing techniques, in vitro patch-clamp recordings and three -dimensio nal reconstruction of recorded neurones in adult hypothalamic slices. 2, The results showed that PVN pre-autonomic neurones constitute a heteroge neous neuronal population. Based on morphological criteria, neurones were c lassified into three subgroups, Type A neurones (52 %) were located in the ventral parvocellular (PaV) subnucleus, and showed an oblique orientation w ith respect to the third ventricle (W). Type B neurones (25%) were located in the posterior parvocellular (PaPo) subnucleus, and were oriented perpend icularly with respect to the 3V. Type C neurones (23 %) were located in bot h the PaPo (82 %) and the PaV (18 %) subnuclei, and displayed a concentric dendritic configuration. 3. A morphometric analysis revealed significant differences in the dendriti c configuration among I neuronal types. Type B neurones had the most comple x dendritic arborization, with longer and more branching dendritic trees. 4. Several electrophysiological properties, including cell input resistance and action potential waveforms, differed between cell types, suggesting th at the expression and/or propel-ties of a variety of ion channels differ be tween neuronal types. 5. Common features of PVN pre-autonomic neurones included the expression of a low-threshold spike and strong inward rectification. These properties di stinguished them from neighbouring magnocellular vasopressin neurones. 6. In summary, these results indicate that PVN pre-autonomic neurones const itute a heterogeneous neuronal population, and provide a cellular basis for the study of their involvement in the pathophysiology of hypertension and congestive heart failure disorders.