INCIDENCE OF NEURONAL COUPLING IN SUPRAOPTIC NUCLEI OF VIRGIN AND LACTATING RATS - ESTIMATION BY NEUROBIOTIN AND LUCIFER YELLOW

Dye coupling among neurons has been shown to reflect electrotonic coup ling. Recent work in retina has revealed that the incidence of couplin g is greater when estimated by neurobiotin (NB) transfer than by Lucif er yellow (LY). Several previous studies have shown that the incidence of LY coupling among supraoptic nucleus (SON) neurons of lactating ra ts is 2- to 4-fold higher than is observed in virgin females. We compa red the incidence of coupling among SON neurons following simultaneous injections of LY and NB into the same cells in slices from virgin or lactating rats. As seen in previous studies, there were 4-fold more LY -coupled neurons per injection in lactating as compared to virgin rats . Under both conditions, the numbers of NB-coupled neurons per injecti on were 4-fold greater than was observed for LY; possible mechanisms a re discussed. Individual NB-filled neurons were coupled to as many as 10 other cells distributed over a large area of the SON. These results confirm previous findings of more coupling in lactating than virgin S ONs, and suggest that both the incidence and spatial extent of interne uronal coupling are greater and thus probably more important functiona lly than has been heretofore appreciated.