title: Electron microscopic examination of the endomorphin 2-like immunoreactive neurons in the rat hypothalamus.
abstract: Endomorphins are endogenous opioid peptides with high affinity and selectivity for the mu-opioid receptor. In the present study, we examined the morphology of the endomorphin 2-like immunoreactive (EM2-LI) neurons in the hypothalamus at the light and electron microscopic levels. At the light microscopic level, EM2-LI neurons were found mostly distributed in the regions between the dorsomedial and ventromedial hypothalamic nuclei and the region near the third ventricle. At the electron microscopic level, EM2-LI perikarya could be divided into two groups. Type I perikarya contained relatively undeveloped endoplasmic reticulum and Golgi apparatus while type II perikarya contained well-developed rough-surfaced endoplasmic reticulum and Golgi apparatus. Both type I and type II neurons contained numerous EM2-LI dense-cored vesicles. Type II perikarya and dendrites received synapses and showed immunoreactivity in the endoplasmic reticulum and Golgi apparatus. EM2-LI axon terminals formed synapses with both immunonegative and immunopositive dendrites. In some cases, the axon terminals contained both immunonegative and immunopositive dense-cored vesicles. EM2-LI neurons often had synaptic relationships with neurons containing immunonegative dense-cored vesicles. Myelinated axon shafts containing EM2-LI were also found. This first demonstration of the ultrastructure and synaptic relationships of EM2-LI neurons in the hypothalamus provides morphological evidence that suggests (1) endomorphin 2-containing neurons modulate physiological function through synaptic relationships; (2) endomorphin 2 may coexist with other neurotransmitters in the same neurons; and (3) endomorphin 2-containing neurons could modulate other endomorphin 2-containing neurons as well as those containing other neurotransmitters.
authors.affiliation: Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, 142-8555, Tokyo, Japan.
authors.forename: Q-P
authors.initials: QP
authors.lastname: Wang
authors.forename: J E
authors.initials: JE
authors.lastname: Zadina
authors.forename: J-L
authors.initials: JL
authors.lastname: Guan
authors.forename: A J
authors.initials: AJ
authors.lastname: Kastin
authors.forename: S
authors.initials: S
authors.lastname: Shioda
mesh_terms: D000818:Animals; D007034:Hypothalamus, Posterior / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D007150:Immunohistochemistry; D002479:Inclusion Bodies / Q000378:metabolism; D008297:Male; D016253:Microscopy, Immunoelectron; D009434:Neural Pathways / Q000378:metabolism / Q000648:ultrastructure; D009474:Neurons / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D009842:Oligopeptides / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D009842:Oligopeptides; C105294:endomorphin 2