Dense plexus of substance P immunoreactive nerve terminals in eminentia medialis of the primate hypothalamus

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Abstract
The indirect immunofluorescence technique of Coons and collaborators was used to study distribution of substance P-like and luliberin (luteinizing hormone-releasing hormone)-like immunoreactivity in the eminentia mediana (eminentia medialis of infundibulum) of rats, monkeys [Cercopithecus sabaeus] and humans. In rats, abundant luliberin-positive fibers were present in the external layer (mainly lateral parts); almost no substance P-immunoreactive nerves were observed in this region. In the external layer of the primate eminentia medialis a dense plexus of substance P-positive nerve terminals was observed close to the blood vessels supplying the anterior pituitary gland. Luliberin-immunoreactive fibers were present, but with a more even distribution all over the eminentia medialis and in lower numbers. Substance P may play a role in control of hormone secretion from the anterior pituitary, either by being released into the portal vessels, i.e., acting as a releasing or inhibitory hormone or by an action as local regulator (modulator or transmitter) at the eminentia medialis level. Substances other than the classical releasing and inhibitory hormones may be important for regulation of the pituitary gland. There may exist marked species differences with regard to type of substances involved in central control of the pituitary.