A new fixation procedure for study of the histaminergic neurons by immunoelectron microscopy using the direct antiserum against histamine.

A new perfusion protocol was developed to detect histamine-like immunoreactive neurons at the electron microscopic level. By stepwise perfusion of 1-ethyl-3(3-diamethylaminopropyl)-carbodiimide and paraformaldehyde solutions, the brain block could be cut with a vibratome and the immunoreactivity could be detected using the avidin-biotin-peroxidase-complex method. We used this method to study the ultrastructure and synaptic relations of the histaminergic neurons in the postmammillary caudal magnocellular nucleus of the rat hypothalamus. This method should also be useful for examination of histaminergic neurons in other tissues and the synaptic relations of histaminergic neurons with other neurotransmitter-containing neurons by double immunostaining.