Neuroendocrine regulation of sexually dimorphic brain structure and associated sexual behavior in male rats is genetically controlled.
Steroid hormones, particularly 17beta-estradiol (E2), regulate the development and expression of neural structures and sexual behavior. Recently, we demonstrated that E2-regulated responses are controlled by quantitative trait loci. In this study, we quantified 1) volume of the sexually dimorphic nucleus (SDN) of the preoptic area (POA); 2) medial basal hypothalamic (MBH)-POA aromatase and 5alpha-reductase enzyme activities during prenatal development and in adults; 3) serum LH, testosterone, FSH, E2, prolactin (PRL), and corticosterone levels; 4) reproductive organ (i.e., testis and ventral prostate) weights; and 5) male mating behavior in Noble (NB/Cr) and Wistar-Furth (WF/NCr) rat strains to determine the genetic influence on the measured parameters. Maximal phenotypic divergence in male SDN-POA volumes was seen between NB/Cr versus WF/NCr and BDIX/Cr rats (among nine rat strains initially examined), with the average SDN-POA volume of NB/Cr male rats being significantly greater ( approximately 30%) than that of either WF/NCr or BDIX/Cr males. Subsequent experiments investigated WF/NCr versus NB/Cr male rats in further detail. Significantly higher MBH-POA aromatase activity was seen in adult WF/NCr versus NB/Cr males, while MBH-POA 5alpha-reductase rates were not significantly different (within or between sex) for the two rat strains assayed. Serum LH levels were significantly higher (by greater than sixfold) in WF/NCr versus NB/Cr males, whereas testis organ:body weight and ventral prostate:body weight ratios in WF/NCr versus NB/Cr males were significantly smaller (by approximately 6-fold for testis and approximately 1.5-fold for prostate values). Serum FSH levels were significantly higher (by twofold) in WF/NCr versus NB/Cr males. However, serum testosterone levels were not significantly different, whereas E2 levels were approximately twofold higher (but not significantly different) in WF/NCr versus NB/Cr animals. No significant differences were found in basal (i.e., nonstress) serum PRL or corticosterone levels between the WF/NCr and NB/Cr males. In male copulatory tests, NB/Cr males exhibited significantly more aggressive sexual behavior (e.g., in mounting, intromission, and ejaculation parameters) compared with WF/NCr males. Taken together, these findings indicate that WF/NCr males are, in general, low responders, whereas NB/Cr males are high responders to hormonal signals. The obtained data suggest that the correlative, phenotypic variation in SDN-POA volume (i.e., structure) and reproductive hormone patterns and mating behavior (i.e., function) of WF/NCr versus NB/Cr males is regulated by potentially E2-mediated mechanisms that are genetically controlled.
Lephart
E D
ED
Neuroscience Center, 633 WIDB, Brigham Young University, Provo, UT 84602, USA. edwin_lephart@byu.edu
Call
S B
SB
Rhees
R W
RW
Jacobson
N A
NA
Weber
K S
KS
Bledsoe
J
J
Teuscher
C
C
D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001835:Body Weight / Q000502:physiology; D001921:Brain / Q000254:growth & development*; D003307:Copulation / Q000502:physiology; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D004958:Estradiol / Q000235:genetics / Q000502:physiology; D005824:Genetics, Behavioral; D012739:Gonadal Steroid Hormones / Q000235:genetics* / Q000502:physiology*; D007033:Hypothalamus, Middle / Q000033:anatomy & histology / Q000502:physiology; D008297:Male; D009490:Neurosecretory Systems / Q000502:physiology*; D009929:Organ Size / Q000502:physiology; D010641:Phenotype; D011301:Preoptic Area / Q000033:anatomy & histology / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012727:Sex Characteristics; D012726:Sexual Behavior, Animal / Q000502:physiology*
D012739:Gonadal Steroid Hormones; D004958:Estradiol; D003577:Cytochrome P-450 Enzyme System; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase