Paraventricular hypothalamic nucleus stimulation modulates nociceptive responses in dorsal horn wide dynamic range neurons

Effects of different parameters of hypothalamic paraventricular nucleus (PVN) electrical stimulation on somatic responses, in dorsal horn neurons were examined. In anaesthetized rats, single-unit extracellular recordings were made from dorsal horn lumbar segments, which receive afferent input from the toe and hind paw regions. We compared the neuronal responses evoked by electrical stimulation of the receptive field (RF) with the responses preceded by ipsilateral PVN stimulation. Only the responses corresponding to Aδ and C-fiber activation were inhibited when PVN stimulation was delivered. Fast-evoked responses corresponding to Aβ fibers were not modified. The magnitude of inhibition depends on the intensity and duration of the PVN stimulation train and gradually decreases as the time interval between the PVN and RF stimulations increases. The results indicate that PVN modulates nociceptive, but not non-nociceptive neuronal responses at the spinal cord level, and this modulation depends on the parameters of the stimulus utilized to activate PVN neurons.