Paraventricular neurosecretory neurons: synaptic inputs from the ventrolateral medulla in rats

Effects of electrical stimulation of the ventrolateral medulla on discharge activity of neurosecretory neurons in the paraventricular nucleus (PVN) were studied in male rats anesthetized with urethane-chloralose. Among 35 phasically firing neurosecretory neurons, stimulation of the lateral reticular nucleus and its vicinity produced excitation in 10 and inhibition in 2. The stimulation also enhanced the activity of 40% of the PVN neurosecretory neurons that fired continuously (n = 81); of these responsive neurons, half of the neurons tested (n = 12) were inhibited by i.v. administration of phenylephrine. The result suggests that both vasopressin- and oxytocin-secreting neurons in the PVN receive mainly excitatory synaptic inputs from the ventrolateral medulla.