Expression pattern of histaminergic neurons in the human fetal hypothalamus at second and third trimester

The hypothalamic nuclei constitute that part of the corticodiencephalic mechanism that activates, controls and integrates the peripheral, autonomic mechanisms, endocrine activity and many somatic functions. Their full integration into behavior requires the neocortex, in particular the limbic system.

An antiserum against histamine was used to reveal the location and time of appearance of the amine in developing fetal hypothalamus. Although the expression pattern of histamine is well studied in mammals, less is known about it in humans. The neurotransmitter histamine plays a crucial role in co-ordinating mutiple inputs from various brain centres.

In the present investigations the hypothalamus was studied in the human fetus ranging from 19 weeks of gestation (GW) to term by using immunocytochemistry. Distinct neurons that stained with Pischinger's methylene blue were obsereved from 19 GW to term. Sections adjacent to those that contained neurons were stained for histamine labeling. Immunoreactive neurons in the hypothalamus at 19 GW of gestation show relatively meager population.

Histamine immunoreactive (His-ir) neurons of the hypothalamus were divisible in lateral and ventrolateral subgroups at 19 GW to 24 GW At 32 GW along with the neuronal cell bodies some beaded fibers were visible. There was progressive increase in the histamine expressing neurons as the fetus grows. In term fetal specimens, two to three small groups of his-ir neurons gradually merged in a single large ventrolateral group.

The findings of the present study provide for a better understanding of the chemoneuroarchitecture of histamine containing neurons in hypothalamus during second and third trimester of human fetal development.