THE PARAVENTRICULAR NUCLEUS OF THE HYPOTHALAMUS SENDS EFFERENTS TO THE SPINAL-CORD OF THE RAT THAT CLOSELY APPOSE SYMPATHETIC PREGANGLIONICNEURONS PROJECTING TO THE STELLATE GANGLION

Using a combination of anterograde and retrograde neuronal tract-traci ng techniques, the descending projections from the paraventricular nuc leus of the hypothalamus (PVN) to the brain/spinal cord and in particu lar those axonal projections that appear to be contiguous with sympath etic preganglionic neurones (SPN) projecting to the stellate ganglion have been studied. Descending PVN pathways were located by the anterog rade transport of biotinylated dextran amine (BDA), whilst SPN were re trogradely labelled with cholera B toxin subunit conjugated to horsera dish peroxidase (CB-HRP). BDA-labelled PVN axons terminated in both hy pothalamic and extrahypothalamic (including the midbrain, medulla and spinal cord) brain nuclei, with dense terminal labelling observed part icularly in the arcuate hypothalamic nucleus and adjacent median emine nce, in the solitary tract, vagal nuclei and in the intermediolateral region of the spinal cord (IML). Varicose descending PVN fibres in the IML were often observed to closely appose both the cell soma and dend rites of retrogradely labelled SPN (projecting to the stellate ganglio n) in the spinal cord. In addition, it was shown that PVN descending a xons crossing to the contralateral side of the spinal cord were closel y associated with retrogradely labelled SPN projecting to the superior cervical ganglion. Such findings suggest that descending pathways fro m the PVN may exhibit a direct influence on cardiac sympathetic outflo w and may also influence the behaviour of the contralateral population of SPN projecting to the superior cervical ganglion.