Summary
To evaluate the relationship of the extrahypothalamic brain thyrotropin-releasing
hormone (TRH) to its hypothalamic counterpart, we studied the maturation of hypothalamic
and extrahypothalamic TRH in the rat. The absolute increase of TRH in the whole brain
and the extrahypothalamus reached adult levels at 7 days of age, whereas the hypothalamic
TRH concentrations did not differ from the adult levels at 23 days. Moreover, the
TRH concentrations at 7 days were greater than the adult levels in the striatum, hippocampus,
pons-medulla and cerebellum, and similar to the adult levels in the midbrain and cortex.
These data indicate the developmental divergency of hypothalamic and extrahypothalamic
TRH, implying that the maturation of extrahypothalamic TRH is independent of the hypothalamus.
The present study suggests that extrahypothalamic TRH may play a neurophysiological
role in the central nervous system at an early infantile age, at which hypothalamic
TRH is not ripe for its endocrinological action.
Key-Words:
TRH
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Ontogeny
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Hypothalamus
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Extrahypothalamus
