Catecholamine Turnover Rates in Discrete Hypothalamic Areas and Associated Changes in Median Eminence Luteinizing Hormone-Releasing Hormone and Serum Gonadotropins on Proestrus and Diestrous Day 1*

Abstract

We have correlated catecholamine [CA; i.e. norepinephrine (NE), dopamine (DA), and epinephrine (E)] turnover rates in discrete hypothalamic nuclei and in the median eminence (ME), with concentration changes in ME LHRH and serum LH, FSH, PRL, estradiol, and progesterone levels at various times during proestrus and diestrous day 1 in 4-day cyclic rats. CA concentrations were measured with a radioenzymatic assay at 0, 60, and 120 min after ip injection of 400 mg/kg alpha-methyl-p-tyrosine, and rate constants and turnover rates were calculated. In a separate assay NE, DA, and E were separated by two-dimensional thin layer chromatography, and concentrations and turnover rates of CAs were calculated. The microdissected hypothalamic nuclei examined for NE turnover rates included the medial preoptic nucleus (MPN), suprachiasmatic nucleus (SCN), arcuate nucleus (AN), and ME. DA turnover rates also were measured in the MPN, ME, and AN. ME LHRH and serum hormone concentrations were measured by RIA. Between 0900--1200 h, proestrous serum estradiol was elevated, but other serum hormones were basal, and CA turnover rates in the brain were low. However, ME LHRH concentrations increased significantly between 0900--1200 h on proestrus. Between 1200--1500 h, serum LH, FSH, PRL, and progesterone levels increased and ME LHRH levels declined significantly; during this time interval (1200--1400 h), a significant rise in ME NE and DA turnover rates occurred. Between 1500--1700 h on proestrus, while serum gonadotropins were still rising toward peak concentrations, increased ME NE turnover rates were maintained, but increased NE turnover rates also were evident in MPN, SCN, and AN. During this same time interval (1500--1700 h), a marked decline in ME and AN DA turnover rates occurred, although such rates remained unchanged within the MPN. There were no corresponding changes in MPN E turnover rates at any of the time intervals studied. The increased turnover rates of ME NE coupled with the concomitant decline in ME LHRH levels and the rise in plasma LH and FSH levels suggest that increased NE release may be important in initiating preovulatory LH and FSH surges. These changes in brain neurotransmitters and serum hormones are not the result of a diurnal rhythm, since corresponding changes in CA turnover rates or serum gonadotropins did not occur between 0900--1100 h and 1500--1700 h diestrous day 1.

Variations in the Hypothalamic-Pituitary-Adrenal Response to Stress during the Estrous Cycle in the Rat

“…Hypothalamic 5-HT content varies over the estrous cycle (Rozsahegyi et al, 1973), and estrogen has been known to cause an acute biphasic up-and down-regulalion of 5-HT receptors (Biegon and McEwen, 1982). Likewise during early proestrous, estrogen increases NA and DA turnover rate in various hypothalarnic nudei induding the 52 suprachiasmatic nucleus and the median eminence (Rance et al, 1981;Wise et al, 1981).…”

“…The pattern of LHRH content in these discrete hypothalamic areas have been shown to parallel the changes in ME LHRH content occurring during proestrous. Thus, it has been concIuded that the hypothalamic LHRH system functions as an integrated unit regulating the release of LHRH from the ME (Wise et al, 1981). The extensive distribution ofLHRH in the hypothalamus suggests that UIRH can probably affect other hypophysiotropic factors.…”

Changes in α-estradiol receptor and progesterone receptor expression in the locus coeruleus and preoptic area throughout the rat estrous cycle

“…It should be noted that estradiol increases noradrenergic turnover before and during the proestrus LH surge in several brain areas, including the POA and median eminence (Rance et al 1981, Mohankumar et al 1994, and that an increased noradrenergic input to POA is essential for the synthesis as well as for the release of GnRH (Herbison 1997). In LC neurons, estradiol stimulates gene expression of TH and dopamine beta hydroxylase (Serova et al 2002), probably by acting through ER.…”

Menstrual cycle phase modulates cognitive control over male but not female stimuli

“…Oestrogen and progesterone have direct and opposing actions on dopaminergic neurotransmission. Preclinically, oestrogen increases dopamine synthesis (Pasqualini et al 2005;, turnover and release (Becker and Beer, 1986), and dopamine receptor density (Hruska andSilbergeld, 1980 andRance et al, 1981b), as well as decreasing monoamine activity which reduces the degradation of dopamine (Luine et al, 1975). In contrast, progesterone appears to down-regulate dopamine systems (Shimizu et al, 1993), leading to the suggestion that the results reported in this study may be influenced by the facilitatory effect of oestrogen on the dopaminergic system during the follicular phase of the menstrual cycle.…”