DEPOLARIZING ACTION OF SECRETORY GRANULE PROTEIN-7B2 ON RAT SUPRAOPTIC NEUROSECRETORY NEURONS

A novel precursor neuropeptide termed 7B2 is present within specific b rain areas, including the hypothalamic magnocellular neurosecretory ne urons, and appears to be processed to smaller fragments. In order to d etermine whether specific C-terminal fragments of 7B2 might exert loca l effects on neurosecretory cells, we used intracellular current-clamp recordings in supraoptic neurons maintained in superfused hypothalami c explants to evaluate membrane potential and resistance changes in 25 supraoptic nucleus neurons during bolus applications of 7B2(174-186) and two other C-terminal peptide fragments 7B2(156-173) and 782(141-15 0). In 15 supraoptic neurons, only the 7B2(174-186) fragment induced a gradual 2-8 mV membrane depolarization that lasted for 4 to 30 min an d was accompanied by 15+/-8% reduction in input resistance. Immunocyto chemical identification of the recorded cells revealed that both vasop ressin (VP)- and oxytocin (OT)-containing neurons were depolarized by 7B2(174-186). These data suggest that 7B2(174-186) is a biologically a ctive fragment of 7B2 and may regulate the excitability of magnocellul ar supraoptic nucleus neurons.