Alberto J. Carrillo

Estrogen receptors in the medial basal hypothalamus of the rat following complete hypothalamic deafferentation

This study was designed to investigate the effect of complete hypothalamic deafferentation (CHD) on the estrogen receptor (ER) concentration in the MBH as well as LH and FSH secretion. Adult female rats underwent CHD using a Halasz-Pupp knife. Sham CHD and intact animals served as controls. Five days after CHD all the rats were ovariectomized and 2 days later they were decapitated and trunk blood collected and the plasma analysed for LH and FSH by radioimmunoassay (RIA). The brains were rapidly removed and the MBH and preoptic area (POA) were dissected. Brain tissues were homogenized in 2.0 ml of phosphate buffer, centrifuged and the supernatant (cytosol) withdrawn. The cytosols were then incubated at 0–4°C for 3 h with [3H]E2 or [3H]E2 + unlabeled E2. Bound and free receptor was separated using 5–30% sucrose gradient centrifugation, Sephadex LH-20 column or hydroxylapatite receptor assays. CHD resulted in a significant (P < 0.05) reduction in the concentration of ER in the MBH when compared with controls. ER concentration in the POA of the CHD group was not significantly different from the control group. CHD also resulted in a significant (P < 0.005) reduction in the plasma concentration of LH and FSH when compared with the controls. These data suggest that the estrogen receptors in the MBH are influenced by the connections with extrahypothalamic regions and that the effect of hypothalamic deafferentation on gonadotropin secretion may be in part secondary to this reduction of receptors in the MBH.

Stimulation of the Hippocampus and Ovulation in the Rat: Specific or Nonspecific Effects

Bilateral electrochemical stimulation (ECS) of the ventral hippocampus (VHPC) or dorsal hippocampus (DHPC) under acute condition at 10.00, 12.00 or 13.00 h on proestrus did no interfere with ovulation. When the same ECS of the VHPC was repeated at 12.00 h proestrus followed by the taking of blood samples at 14.00, 16.00 and 18.00 h under ether anesthesia from the jugular vein, the LH surge and ovulation were significantly (p less than 0.05) inhibited. Acute unilateral ECS of the VHPC or passing the same current through a platinum electrode had no effect on the LH surge. When large electrolytic lesions were bilaterally made in the VHPC with a platinum electrode at 12.00 h of proestrus followed by blood samples, the LH surge and ovulation were also inhibited (p less than 0.05). Large lesions in the caudate putamen also resulted in a significant (p less than 0.05) suppression of the LH surge and the number of ova. These data suggest that (1) electrochemical stimulation of the hippocampus is not inhibitory to ovulation, and (2) acute procedures on the day of proestrus can inhibit LH secretion.

Hyperprolactinemia attenuates ovarian steroid stimulation of region-specific hypothalamic serotonin synthesis and luteinizing hormone release in ovariectomized rats

Hyperprolactinemia adversely affects reproductive functions, presumably through an effect at the hypothalamic level. Given the numerous published reports linking hypothalamic serotonin (5-hydroxytryptamine, 5HT) mechanisms to the regulation of gonadotrophin secretion, we sought to determine the effects of experimentally induced hyperprolactinemia on ovarian steroid-induced increases in serum LH levels and region-specific hypothalamic 5HT synthesis in ovariectomized rats. In the first study, bilaterally ovariectomized Sprague-Dawley rats either received two pituitary homografts implanted beneath the left kidney capsule or were sham-grafted. Both groups of rats were injected subcutaneously with 5 micrograms/100 g of estradiol benzoate (E2) in corn oil vehicle at 08.00 h, 1 and 2 days before serum collection and 5 mg/100 g of progesterone (P) in corn oil vehicle at 07.00 h on the day of serum collection. Blood samples were collected via chronic indwelling jugular cannulae from each rat at 10.00, 12.00, 13.00, 14.00, 16.00 and 18.00 h. A statistically significant elevation in serum LH levels was detected at 13.00, 14.00 and 16.00 h. This increase in serum LH levels was significantly attenuated in rats bearing pituitary homografts, an effect attributed to the high serum PRL levels measured in these animals. In the second study, bilaterally ovariectomized Sprague-Dawley rats were divided into three experimental groups: (1) rats bearing two pituitary homografts and injected with E2 and P on the schedule and at the dosages previously described, (2) sham-grafted rats injected with E2 and P on the schedule and at dosages previously described and (3) sham-grafted rats injected with corn oil vehicle only.(ABSTRACT TRUNCATED AT 250 WORDS)

Episodic Corticosterone Secretion in the Female Rat

Studies conducted in several laboratories have shown primate glucocorticoid secretion to occur episodically. In light of the methodological, as well as physiological importance of this finding, the present study was undertaken to determine whether the rat corticosteroid secretion also occurs episodically. Female rats were outfitted with chronic intravenous cannulas, and 1 week later 200 units of heparin were injected through the implanted cannula and blood samples (0.3-0.4 ml) were collected from each rat every 10 min for 3 h during the morning (06.00-10.00 h) or during the afternoon (16.00-19.00 h) (lights on from 05.00 to 19.00 h). Plasma corticosterone levels in cannulated rats showed fluctuations indicative of episodic secretion. The pattern of plasma corticosterone levels was characterized by periodic rapid increases in hormone concentration during both the morning and afternoon sampling periods; the occurrence of these hormonal fluctuations did not have a characteristic frequency. When the data were grouped to obtain single morning and afternoon values, the AM-PM difference was significant (p < 0.005). Collectively, these data suggest that in the rat, adrenal corticosteroids are secreted episodically.

The medial basal hypothalamus and luteinizing hormone release in the rat: Where are the LH-RH neurons responsible for tonic gonadotropin secretion?

Abstract Careful review of the literature demonstrates conflicting results concerning the ability of the deafferented medial basal hypothalamus to support gonadotropin release in the rat and thus one may question the existence of LH-RH neurons in the medial basal hypothalamus. The direct search for the LH-RH perikarya in the rat hypothalamus has not settled the question of whether these releasing hormone neurons are located in the medial basal hypothalamus. Most investigators do agree that following complete hypothalamic deafferentation there is a reduction of the immunoassayable LH-RH in the medial basal hypothalamus; however, these results do not necessarily prove that LH-RH originates outside the hypothalamus. It is argued that the completely deafferented medial basal hypothalamus may be so altered by the deafferentation procedure that it may be inadequate as a means to study neuroendocrine function.

Plasma LH levels in the long term ovariectomized rat after anterolateral deafferentation of the medial basal hypothalamus and lesions in the medial preoptic area.

This study was designed to investigate the effect of anterolateral hypothalamic deafferentiation (ALHD) and medial preoptic area (MPOA) lesions on plasma LH levels in the long term ovariectomized rat. The deafferentations were carried out with a Halasz-Pupp knife (radius of 1.5 mm and height of 2.0 mm) and the MPOA lesions with a platinum electrode. Sham treated and an intact group served as controls. Blood samples were obtained from the jugular vein under light ether anesthesia before and at 1, 2, 4 and 6 weeks after brain surgery. After the sixth week sample all rats were treated with 50 micrograms of estradiol benzoate (EB) and two days later blood samples were collected during the morning and afternoon. Hypothalamic deafferentation resulted in a more significant (p less than 0.01) drop in plasma LH levels in one half of the group (ALHD-1) than in the other half (p less than 0.05) (ALHD-2) when compared to the controls. Treatment of the controls with EB resulted in a significant (p less than 0.01) depression of LH levels in the morning and an LH surge during the afternoon. EB also resulted in a suppression (p less than 0.01) of LH levels during the morning in all of the ALDH rats; however, only the ALHD-1 group had an LH surge during the afternoon following EB. Plasma LH levels in the ALHD-2 remained suppressed during the afternoon after EB treatment. Lesions in the MPOA had no effect on plasma LH levels at 1 to 6 weeks when compared to controls. Treatment of the MPOA lesion group with EB resulted in a significant (p less than 0.01) drop in plasma LH levels during the morning as well as the afternoon. These data suggest that the fibers that are critical for the control of tonic and phasic LH secretion enter the medial basal hypothalamus laterally and that the deafferentations carried out here were selective in interrupting fibers involved with tonic LH secretion in some rats and those involved with the phasic secretion in others. These data also suggest that the MOPA components involved with tonic LH secretion are separate from those controlling phasic LH secretion.