Ultrastructural evidence for luteinizing hormone-releasing hormone neuronal control of estrogen responsive neurons in the preoptic area.
Both estrogen receptor (ER) immunoreactive (ir) and LHRH-ir neurons and processes are present in the preoptic area of the guinea pig. This experiment was conducted to determine if LHRH-ir terminals interact synaptically with ER-ir cells. A light microscopic dual chromogen immunocytochemical technique employing diaminobenzidine (DAB) and nickel-enhanced DAB for LHRH and ER localization, respectively, revealed that many varicose LHRH-ir fibers coursed in close proximity to ER-ir cells in the anterior part of the preoptic area at the preventricular periventricular nucleus (Pep), suggesting the likelihood of synaptic interactions. Ultrastructural analysis was performed using DAB and 3,3',5,5'-tetramethylbenzidine (TMB) for LHRH and ER localization, respectively. DAB labeling in LHRH-ir neurons appeared as a dense flocculent product dispersed throughout the cytoplasm. TMB stained ER-ir neurons contained electron dense crystalline spicules located predominantly in their nuclei. Numerous TMB labeled ER-ir neurons were present in the Pep, and occasionally occurred in clusters, closely apposed to one another. Many LHRH-ir terminals made synaptic contact or were apposed to unlabeled dendrites, while fewer contacted perikarya. Most significantly, ER-ir neurons showing clear evidence of intranuclear TMB crystals received synaptic input from LHRH-ir terminals. In addition, LHRH-ir terminals lacking synaptic specializations were also in direct apposition to ER-ir perikarya. These results provide morphological evidence that LHRH-ir neurons can regulate ER-ir neurons in the preoptic area. Since LHRH-ir cells are thought to be regulated by estrogen responsive neurons, interaction of LHRH terminals with ER-ir cells may represent a regulatory feedback circuit between the two systems.
Langub
M C
MC
Department of Anatomy and Neurobiology, University of Kentucky Medical Center, Lexington 40536-0084.
Maley
B E
BE
Watson
R E
RE
D015100:3,3'-Diaminobenzidine; D000818:Animals; D000911:Antibodies, Monoclonal; D001560:Benzidines; D002863:Chromogenic Compounds; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000032:analysis*; D006168:Guinea Pigs; D016253:Microscopy, Immunoelectron; D009474:Neurons / Q000502:physiology / Q000648:ultrastructure*; D011301:Preoptic Area / Q000166:cytology / Q000648:ultrastructure*; D011960:Receptors, Estrogen / Q000032:analysis*; D013569:Synapses / Q000648:ultrastructure*
D000911:Antibodies, Monoclonal; D001560:Benzidines; D002863:Chromogenic Compounds; D011960:Receptors, Estrogen; D015100:3,3'-Diaminobenzidine; D007987:Gonadotropin-Releasing Hormone; C021758:3,3',5,5'-tetramethylbenzidine