The mammalian pituitary intermediate lobe: An update on innervation and regulation

The pituitary intermediate lobe (IL) in mammals is an area of uniform endoc rine cells which synthesize and release specific peptide products of the pr oopiomelanocortin gene. The lobe receives direct synaptic connections onto the endocrine cells from hypothalamic dopaminergic neurons. This review upd ates information on the dopaminergic as well as the gamma -aminobutyric aci d inhibitory neuroregulation for the IL. It also provides a discussion of s timulatory molecules which are likely to affect peptide release, particular ly the neurotransmitter serotonin, which may be present via uptake into the dopaminergic nerve terminals. Other stimulatory molecules discussed which are likely to significantly affect peptide secretion are norepinephrine, co rticotropin-releasing factor, and several opiate peptides. A new direction of study involves the potential interaction of neurotrophic factors, which are present in all areas of the pituitary, and may be suggested to have a s upportive role for the neural elements of the IL. The endocrine cells of th e It and their direct hypothalamic innervation are considered to be an easi ly accessed peripheral model for study of both neural-endocrine and neurotr ophic-target cell interactions, (C) 2001 Elsevier Science Inc.