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Biomedical subjects

J A Colombo

Publications and source records attributed to J A Colombo.

At least 55 records · Page 3Linked to original sources
PubMed1981

Facilitated thyrotropin release after retrochiasmatic hypothalamic knife cuts.

Diencephalic structures that influence plasma thyrotropin (TSH) in male rats under pentobarbital anesthesia (35 mg/kg, IP) were studied by combining medial preoptic area-suprachiasmatic nucleus (MPOA-Sch) bilateral electrical stimulation (monophasic pulses, 200 microA at 50 Hz, 30 min) with progressive midline lesions produced by a retractable Halász knife. Plasma TSH was measured by radioimmunoassay just before (0 time) and at 30, 60 and 90 min after the beginning of stimulation. Rats that had received only sham surgical procedures 90 days prior to stimulation were characterized by a more than 2-3 fold elevation in basal (0 time) plasma TSH levels when compared to those found in intact control rats and expected elevations in plasma TSH at 30 min after stimulation were eliminated. After a small frontal cut (1.3 FC), 0 time plasma TSH levels increased more tha 4-fold above those of controls in association with a facilitation of stimulated release of TSH. When the knife blade radius was 1.5 mm (1.5 FC) the facilitation of TSH release after stimulation occurred again; however, 0 time plasma TSH concentrations in 1.5 FC rats were not different from control levels. These effects of midline cortical, thalamic and hypothalamic damage on TSH release required the passage of more than 12 days after brain surgery. Collectively, these findings suggest potential neural elements that are inhibitory for 'basal' and 'phasic' TSH release which are in close proximity to a separate excitatory neural system and which can be activated by MPOA-Sch stimulation.

Afferent Pathways↗
PubMed1981

Prolactin and luteinizing hormone release after diencephalic lesions and stimulation.

Adult male rats received sham procedures or retrochiasmatic knife cuts of varying sizes. Ten to twelve days (short term survival) or 90 days (long term survival) later animals were placed under pentobarbital anesthesia and pulsed, monophasic (50 Hz, 200 microA, 0.5 msec width, 30 sec on/off) stimuli were delivered during 30 min through bipolar, concentric electrodes bilaterally placed in the medial preoptic-suprachiasmatic nucleus (MPOA-Sch). Blood samples were taken before and at 30 min intervals after stimulation. Plasma prolactin and LH were measured in the same sample. Penetration of the knife guide tube induced a lesion of cortical and subcortical midline structures (sham procedures) placed at or around AP plane 5.0 of the Atlas of Albé-Fessard et al. This resulted in a short term impairment of LH release induced by MPOA-Sch stimulation, an effect that could not be distinguished from the one observed after frontal cuts made with a knife having a 1.5 mm radius (1.5 FC). Frontolateral retrochiasmatic cuts (LFC) blocked the effects of stimulation on LH release. After 90 days, LH response to MPOA-Sch stimulation improved in sham FC and 1.5 FC groups. Sham procedures did not reduce prolactin response after short term survival. 1.5 FC significantly decreased and LFC blocked prolactin release response. Ninety days after FC there was no improvement of prolactin release response to MPOA-Sch stimulation. In conclusion, long term survival after sham and 1.5 FC surgical procedures allowed for a partial recovery of the LH release response, but not that of prolactin, after MPOA-Sch stimulation.

Afferent Pathways↗
PubMed1978

Preoptic-hypothalamic control of LH and prolactin release in male rats under pentobarbital anesthesia: differential responses to electrical stimulation.

In acute experiments under pentobarbital anesthesia, the brains of adult male rats were stimulated bilaterally with trains of monophasic pulses at different frequencies and current intensities through bipolar, concentric, stainless steel electrodes. Stimulation of the POA-SQ region at 3, 10 (200 muA) or 200 Hz (100 muA) increased plasma prolactin levels within 30 min of the onset of stimulation. Stimulus parameters fully effective when applied to the POA-SQ or ARC-MED. EM. regions were ineffective when applied to the ARC-VMH region. Maximal effects were obtained with 10 Hz (200 muA) stimuli applied to the POA-SQ region. LH levels were increased after stimulation of any of the three regions--POA-SQ, ARC-VMH or ARC-MED. EM. Conversely to the prolactin response, LH levels did not rise after 3 Hz stimulation of the POA-SQ region. In male rats under pentobarbital anesthesia, LH levels seemed to be affected maximally with a stimulus frequency rate of about 50 Hz applied to the POA-SQ region. The results suggest a potential physiological role of frequency discrimination in the functional segregation of LH and prolactin release controls.

Anesthesia, General↗
PubMed1976

Effects of limiting water intake on the rat estrous cycle with observations on LH, prolactin, and corticosterone.

By the fifth week of restricting water intake at 1100 to a 15-min period per day, estrous cycle lengths had shifted in most animals (31/40) from 4 to 5 days with the 5-day cycles usually consisting of 3 days of diestrus. In the 5-day cycling rats, plasma corticosterone peaked at 1100 and also at 1900 hr, the proestrous surge in plasma LH was not significantly changed, although the variation in individual animals was greater and the prolactin surge was prolonged. Similar prolonged cycles followed water restriction at 1800 hr with animals returning to regular 4-day cycles when given water to ad libitum. These results suggest that the alteration of the normal corticosteroid rhythm and/or changes in prolactin secretion may account, in part at least, for the changes noted in cycle length after restricting the water intake.

Animals↗
PubMed1975

Limbic system involvement in the increase in plasma prolactin following cortical spreading depression in gonadotropin-treated female rats.

Cortical spreading depression (SD) was induced by applying 25% KCl to the frontal cerebral cortex in female rats under continuous ether anesthesia. Three weeks previously the animals had been subjected to sham operation, bilateral surgical "deefferentation" of the amygdala or transection of the dorsal columns of the fornix. During the week prior to experiment the rats were made "pseudopregnant" by treatment with PMS and hCG. Plasma prolactin was measured by radioimmunoassay in blood samples obtained from the peripheral circulation at 20 min intervals. After two control samples had been taken, KCl was applied to the cortex and sampling continued for another 100 min; In the sham-operated group prolactin levels increased with time following the application of KCl. Fornix-cut animals showed a similar, although briefer, increase with values significantly lower than those found in sham-operated animals at 80 min. The increase in plasma prolactin observed in sham-operated and fornix groups was completely abolished in amygdala-cut animals. These results indicate that limbic structures play a significant role in the mechanisms by which cortical SD elevates plasma prolactin levels under the present experimental conditions.

Amygdala↗
PubMed1975

Effects of spreading depression on stress-induced changes in plasma prolactin and LH.

Female rats rendered "pseudopregnant" by treatment with PMS and hCG and ovariectomized rats injected with estradiol and progesterone (OVX-E2-P) were subjected to cortical spreading depression (SD). Within 7-10 min under ether anesthesia in a stereotaxic instrument a frontal craniotomy was performed and a cotton ball saturated with physiological saline (control) or 25% KCl was applied to the exposed dura, covered with dental cement and skin sutured. The animals were then placed in separate containers in an isolated room and decapitated for collection of trunk blood at 0, 15, 30, or 60 min after surgery. In PMS-hCH saline-treated control animals, prolactin levels had dropped by 15 and 30 min when compared with the zero-time values but by 60 min had increased significantly above the 30-min level. At that time (60 min), prolactin values in the KCl group were significantly lower than in the controls. Corticosterone levels were high at both 15 and 60 min in control and KCl groups. In OVX-E2-P control animals, plasma prolactin levels also rose at 60 min compared with 15- and 30-min samples and at 60 min were significantly higher than in the KCl group. In control animals, LH levels were lower at 15 and 60 min than at zero time, but they remained unchanged in the KCl group. The dato are interpreted as indicating that cortical SD suppresses the stress responses observed in saline-treated control animals.

Animals↗