Postnatal ontogeny of catecholamine and somatostatin neuron systems in the median eminence of the rat as revealed by a colocalization technique.

The ontogenetic development of catecholamine (CA) and somatostatin containing nerve terminals in the rostral, central and caudal median eminence (ME) of the rat was investigated by combining fluorescence histochemistry and immunohistochemistry in the same tissue section. Somatostatin terminals were detected earlier in development than CA terminals and had already appeared in the lateral part of the external layer of the central ME by the 1st postnatal day. CA nerve terminals were first observed in the same region of the ME on the 7th postnatal day. At about this stage both types of terminals seemed to show early signs of a correlation in their distribution which became progressively closer as maturation proceeded. Their distribution reached a stable condition in density and pattern on the 21st postnatal day when the majority were found in the lateral part of the external layer of the central ME, in the basal part of the brain just dorsal to the tuberoinfundibular sulcus and in the upper and lower labia of the tuberoinfundibular stalk. They subsequently matured to the adult pattern of stabilized distribution and anatomical relationship. It was also established that on the 28th postnatal day the somatostatin immunoreactive terminals reached a greater concentration than at any other stage of development including that of the adult.