Distribution of histaminergic axonal fibres in the vestibular nuclei of the cat.

The histaminergic projection in the cat brain originates from neurones located in the tuberomammillary nucleus. The distribution of histaminergic axonal fibres was investigated immunohistochemically in the vestibular nuclei of the cat using an antibody to histamine. Labelled fibres were sparsely distributed in the whole vestibular nuclei complex and were typically beaded with small, darkly stained swellings. Staining density was low to moderate compared with that of other structures in the cat brain. Histaminergic fibre distribution showed spatial variations, with significantly heavier labelling in the superior and medial vestibular nuclei than in the lateral and inferior nuclei. Histamine could play a neuromodulatory role in the processing of sensory afferent information in the vestibular nuclei and in the control of vestibular functions.