Immunohistochemical analysis of the ontogeny of neuropeptide Y immunoreactive neurons in foetal rat brain.

The development of neuropeptide Y-like immunoreactive structures in the foetal rat brain was investigated by means of the indirect immunohistofluorescence technique. Neuropeptide Y-like immunoreactive cells and fibres first appeared on day 13 of gestation, in the solitary tract nucleus, lateral reticular nucleus and nucleus ambiguus in the medulla oblongata, and in the primordial inferior colliculus and deep mesencephalic nucleus. Thereafter, neuropeptide Y-like immunoreactive cells and fibres increased in number in many areas including the primary olfactory cortex, the frontoparietal, somatosensory cortex, caudate putamen, lateral hypothalamus, ventrolateral thalamus, amygdala and parafascicular nucleus. The maximum number of cells over the age range studied, namely day 12 of gestation to birth day, occurred at around day 21. On the day of birth, accordingly, there were significantly fewer neuropeptide Y-like immunoreactive cell bodies in a number of brain areas, the most striking deficit being in the ventrolateral thalamus. The present study demonstrates the very early appearance of neuropeptide Y-like immunoreactive structures during foetal brain development. The functional role of the peptide during this period remains, however, to be determined.