Comparison of the temporal programs regulating tyrosine hydroxylase and enkephalin expressions in TIDA neurons of lactating rats following pup removal and then pup return.

Dopamine (DA) and enkephalin (ENK) release from the tuberoinfundibular dopaminergic neurons (TIDA) into the hypophysial portal circulation is fundamentally different under non-lactating and lactating conditions. The aim of this experiment was to compare the effect of a brief interruption then resumption of suckling on the temporal program of tyrosine hydroxylase (TH; rate-limiting enzyme of dopamine synthesis) and ENK regulation in dams. On post partum day 10, pups were removed for a 4-h period from a group of the dams then returned for 4- and 24-h periods. It was examined whether such a brief interruption of suckling provokes full up-regulation of TH and down-regulation of ENK, and whether reinitiation of suckling limits the extent to which TH up- and ENK down-regulate. At the end of experiment, the animals were decapitated. In situ hybridization was used to examine the expression of TH and ENK mRNA in the arcuate nucleus where TIDA neurons reside. The results showed that, on one hand, the removal of pups induced TH up-regulation, on the other hand, ENK expression also increased 8 h after removal of pups and then started to slowly decline. In dams whose sucklings were reinitiated both TH and ENK mRNAs were up-regulated at least for a day. ENK expression responded more slowly to the removal of pups than expression of TH, and after reinitiation of suckling, the temporal program of regulation of both TH and ENK expressions ran parallel in the first 24 h.

Messenger RNA for neuropeptide Y in the arcuate nucleus increases in parallel with plasma adrenocorticotropin during sepsis in the rat.

Loss of appetite occurs in the cecal ligation and puncture (CLP) model of sepsis in conjunction with the activation of central neural stress pathways. Neuropeptide Y (NPY) in the arcuate nucleus of the hypothalamus is upregulated by several stressors and is stimulatory to feeding. To examine the response of NPY messenger RNA in the arcuate nucleus to sepsis, we used biotinylated RNA probes and a quantitative non-isotopic in situ hybridization approach in cryo-preserved sections from rats made septic by CLP. The mRNA in arcuate neurons was upregulated from the first day after CLP. By the afternoon of the third day through the morning of the fourth day, the average grey level of NPY mRNA clusters was 30% greater after CLP than after sham surgery (P<0.05), and the integrated optical density based on both the grey level and the amount of area with detectable mRNA was 60% greater after CLP than after sham surgery (P<0.03). Both the average grey level and area with detectable staining were positively correlated to plasma ACTH (r=0.953 and 0.917, respectively, n=10 and P<0.01 in each case). Thus sepsis increases the expression of the mRNA for NPY in the arcuate nucleus in proportion to the magnitude of the stress response. However, the suppression of feeding behavior in the CLP model suggests that sepsis activates additional mechanisms that negate the orexigenic contribution of the neuronal increase in NPY mRNA.

Intraspecific variation in estrogen receptor alpha and the expression of male sociosexual behavior in two populations of prairie voles.

Estrogen (E) regulates a variety of male sociosexual behaviors. We hypothesize that there is a relationship between the distribution of estrogen receptor alpha (ERalpha) and the degree of male social behavior. To test this hypothesis, ERalpha immunoreactivity (IR) was compared in prairie voles (Microtus ochrogaster) from Illinois (IL), which are highly social, and Kansas (KN), which are less social. The expression of androgen receptors (AR) in males also was compared between populations. The expression of ERalpha and AR were compared in brains from KN and IL males and females using immunocytochemistry (ICC). There were significant intrapopulational differences, with males expressing less ERalpha-IR than females in the medial preoptic area, ventromedial nucleus, ventrolateral portion of the hypothalamus, and bed nucleus of the stria terminalis (BST). IL males also displayed less ERalpha-IR in the medial amygdala (MeA) than IL females. While IL males expressed significantly less ERalpha-IR in the BST and MeA than KN males, there was no difference in AR-IR. Differences in the pattern of ERalpha-IR between KN and IL males were behaviorally relevant, as low levels of testosterone (T) were more effective in restoring sexual activity in castrated KN males than IL males. The lack of difference in AR combined with lower expression of ERalpha-IR in IL males suggests that behavioral differences in response to T are associated with aromatization of T to E and that reduced sensitivity to E may facilitate prosocial behavior in males.

Cohabitation induced Fos immunoreactivity in the monogamous prairie vole.

Cohabitation of sexually nai;ve male and female prairie voles (Microtus ochrogaster) triggers a cascade of physiological changes that result in the formation of stable pair bonds. In the present study we used the expression of c-Fos protein to identify CNS regions activated during initial social contact in heterosexual, male/male and female/female pairs. Sexually naive males and females were randomly assigned to one of five groups: control- no cohabitation, or cohabitation for 1 h with an unrelated opposite sex, an unrelated same sex, an unfamiliar same sex sibling, or removal for 24 h and then repaired with the familiar sibling. Heterosexual pairing resulted in significant increases in c-Fos immunoreactivity (IR) in the posterodorsal and posteroventral medial amygdala (MeA), bed nucleus of the stria terminalis, medial preoptic nucleus, ventrolateral portion of the ventromedial nucleus of the hypothalamus (VMN-VL) in males and females, and the periventricular nucleus of the thalamus in males only. c-Fos IR during intrasexual cohabitation varied with the relationship of the experimental animal to the stimulus animal. Males cohabited with an unfamiliar unrelated male expressed significantly more c-Fos IR in the central amygdala (CeA). While females cohabited with an unfamiliar female (related or unrelated) also displayed increased c-Fos IR in the CeA, this increase was accompanied by an increase in c-Fos IR in the VMN-VL and MeA. The results from this study suggest that early neuronal activation associated with heterosexual cohabitation is similar in both sexes, while neuronal activation is sexually dimorphic in response to intrasexual cohabitation.