Estrogen-induced dendritic spine elimination on female rat ventromedial hypothalamic neurons that project to the periaqueductal gray.
Neurons of the ventromedial hypothalamic nucleus (VMH) that project to the periaqueductal gray (PAG) form a crucial segment of the motor pathway that produces the lordosis posture, the hallmark of female rat sexual behavior. One suggested mechanism through which estrogen facilitates lordosis is by remodeling synaptic connectivity within the VMH. For instance, estrogen alters VMH dendritic spine density. Little is known, however, about the local VMH microcircuitry governing lordosis nor how estrogen alters synaptic connectivity within this local circuit to facilitate sexual behavior. The goal of this study was to define better the neuron types within the VMH microcircuitry and to examine whether estrogen alters synaptic connectivity, as measured by dendritic spine density, on VMH projection neurons. A retrograde tracer was injected into the PAG of ovariectomized rats treated with vehicle or estradiol. Retrogradely labeled VMH neurons were filled with Lucifer yellow, then immunostained for estrogen receptor-alpha (ER alpha). VMH neurons that project to the PAG had more dendrites than functionally unidentified neurons. Additionally, VMH projection neurons could be subdivided into those located within the cluster of ER alpha-containing neurons and those medial to the cluster. Estrogen decreased spine density by 57% on the long primary dendrites of VMH projection neurons located within the ER alpha cluster but not on projection neurons medial to the cluster. Only 4% of the VMH projection neurons expressed ER alpha. These results suggest that estrogen may facilitate sexual behavior by decreasing spines selectively, via an indirect mechanism, on a subset of VMH neurons that project to the PAG.
Calizo
Lyngine H
LH
Institute of Neurological Sciences, Department of Neurocience, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. lcalizo@mail.med.upenn.edu
Flanagan-Cato
Loretta M
LM
D000818:Animals; D048429:Cell Size / Q000187:drug effects / Q000502:physiology; D003712:Dendrites / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D047628:Estrogen Receptor alpha; D004967:Estrogens / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D005456:Fluorescent Dyes; D007150:Immunohistochemistry; D007546:Isoquinolines; D009434:Neural Pathways / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology*; D010052:Ovariectomy; D010487:Periaqueductal Gray / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011187:Posture / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley / Q000033:anatomy & histology / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism; D012726:Sexual Behavior, Animal / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D014697:Ventromedial Hypothalamic Nucleus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D047628:Estrogen Receptor alpha; D004967:Estrogens; D005456:Fluorescent Dyes; D007546:Isoquinolines; D011960:Receptors, Estrogen; C017475:lucifer yellow