Histamine-immunostaining in the rat median eminence: an unexpected form of cross-reactivity with LH-RH

Abstract

By use of two antisera (αHA-1, αHA-2) raised to histamine (HA) a similar distribution of HA-positive cell bodies and fibres in the rat brain has been demonstrated, except for a dense plexus in the median eminence which was only found with αHA-1. The HA-immunostaining in the median eminence was similar in distribution to that of luteinizing hormone-releasing hormone (LH-RH). In gelatin models containing LH-RH a concentration-dependent increase in immunofluorescence intensity (range: 0.01–10 μM) was found with αHA-1 but not with αHA-2. To evaluate the significance of the cross-reaction of αHA-1 with LH-RH, antero- or postero-lateral deafferentations of the rat mediobasal hypothalamus were made to discriminate between LH-RH and HA projections to the median eminence. The LH-RH- and HA-immunostaining in the median eminence was not affected by posterolateral deafferentations but was abolished in rats with an anterolateral lesion. We conclude that the HA-immunostaining in the rat median eminence is due to a cross-reaction of αHA-1 with LH-RH.