Organization of the histaminergic system in the brain of the turtle Chinemys reevesii.

To accumulate phylogenetic information on the central histaminergic system, we investigated the histaminergic system in the brain of the Reeves turtle, Chinemys reevesii, using the indirect immunofluorescent method with antiserum against histamine. Histaminergic neuronal cell bodies were found exclusively in the posterior part of the ventral hypothalamus. Histaminergic varicose fibers innervated almost all parts of the turtle brain, but tended to be concentrated in several areas. Very dense innervation was observed in the medial part of the telencephalon, ventrolateral part of the hypothalamus, nucleus habenularis lateralis, and ventromedial part of the tegmentum. Medium density of innervation was seen in the olfactory bulb, nucleus medialis amygdalae, and tectum. Only a few fibers were detected in the lateral part of the telencephalon, dorsal part of the hypothalamus, thalamus, rhombencephalon, and spinal cord. The main ascending fibers were observed in the lateral part of the hypothalamus, sending dense fiber bundles to the cortices dorsomedialis and medialis and nucleus habenularis lateralis. Descending fibers appeared to run in the ventral tegmental area, passing through the dorsal and ventral parts of the midline of the brain stem to the spinal cord. These findings indicate that the general morphological features of the histaminergic system in the turtle brain are similar to those in the mammalian and frog brains.