Precise terminal fields of the descending somatostatinergic neuron system from the amygdaloid complex of the rat.

The descending somatostatin (SOM) tract from the amygdaloid complex to the lower brain stem and upper cervical cord in the rat was investigated experimentally by means of the indirect immunofluorescence technique. The present study demonstrates that SOM neurons in the amygdaloid complex send their axons ipsilaterally to various lower brain stem areas and to the upper cervical cord, because destruction of the amygdaloid complex resulted in various degrees of ipsilateral reduction of SOM fibers: a marked decrease in n. reticularis pontis oralis et caudalis, n. reticularis parvocellularis, n. reticularis gigantocellularis, n. reticularis medulae oblongatae pars dorsalis et ventralis and hypoglossal nucleus; a less marked decrease in the midbrain reticular formation, central gray matter of the mesencephalon, facial nucleus and lamina VII of REXED of the upper cervical cord from C1 to C2; and a small decrease in n. reticularis paramedianus and n. reticularis lateralis. These findings were supported by other experiments performed in this study.