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Biomedical subjects

O F Almeida

Publications and source records attributed to O F Almeida.

78 records · Page 5Linked to original sources
PubMed1982

Hypothalamic secretion of thyrotrophin releasing hormone is decreased in male Japanese quail exposed to long daily photoperiods.

Adult male Japanese quail held under short daily photoperiods (8 h light: 16 h darkness; 8L: 16D) had significantly higher plasma concentrations of thyroid-stimulating hormone (TSH), tri-iodothyronine (T3) and thyroxine (T4) than did those kept under long days (16L:8D). When given a single s.c. injection of 50 microgram thyrotrophin releasing hormone (TRH) the birds held under both the 8L: 16D and 16L: 8D photoperiods showed rapid increases in their blood concentrations of TSH, T4 and T3, the amplitude of the TSH response of the birds exposed to 16L: 8D being particularly marked. These results suggest that, in the male quail, long daily photoperiods produce a hypothyroid state as a result of diminished TRH secretion. The synthetic and secretory capacities of the thyroid gland and pituitary thyrotrophs are apparently unimpaired by long days.

Animals↗
PubMed1981

Role of melatonin and circadian rhythms in seasonal reproduction in rams.

In the ram, changes in daylength influence testicular activity by modifying the release of luteinizing hormone-releasing hormone (LH-RH) and thus the gonadotrophins. To investigate the nature of this response the hourly fluctuations in the circulating levels of prolactin, luteinizing hormone (LH) and melatonin were measured in rams kept under various artificial lighting conditions. In Exp. 1, 8 Soay rams (4 control and 4 from which the superior cervical ganglia had been removed) were exposed to alternating 16-week periods of short days (8L: 16D) and long days (16L: 8D) for over 2 years, and blood samples were collected hourly for 25 h on two occasions. The lighting regimen resulted in marked testicular and endocrine changes in the controls but not in the ganglionectomized rams which had low or undetectable levels of melatonin (less than or equal to 33 pg/ml) and an unusual diurnal rhythm in prolactin. In Exp. 2, 8 intact Soay rams were exposed to an ahemeral lighting regimen of 8L: 28D for 16 weeks; at the end of this period blood samples were collected hourly for 52 h and assayed for prolactin. During the pretreatment period of long days (16L: 8D), the testes became fully regressed. During the 16 weeks of 8L: 28D, redevelopment occurred, but the growth of the testes was slow compared to that normally occurring under short days of 8L: 16D. The prolactin profiles showed evidence of circadian rhythm in hormone secretion, with a correlation between the timing and duration of the rhythm and the degree of testicular development. These combined results support the idea that the photoperiodic response in the ram involves an interplay between the secretory activity of the pineal gland, and a light/dark entrained circadian mechanism in the brain.

Animals↗
PubMedDate not supplied

Absence of tolerance to the aversive stimulus properties of ethanol following oral ethanol self-administration.

Depending on the situation, ethanol can serve as a reinforcer in one paradigm and an aversive stimulus in another. The relationships between the two stimuli are not clear, particularly the behavioural adaptation following chronic ethanol exposure. We report on two experiments using an oral-self administration (OSA) paradigm and a conditioned taste aversion (CTA) paradigm. Male Wistar rats were exposed to ethanol using either the OSA or the CTA paradigm, and the consequences were examined in the same groups of rats by performing the other corresponding experiment. Thus, sensitisation or tolerance to the respective stimulus properties of ethanol would be detectable. For OSA experiments, rats were presented, under a free-choice setting, tap water and an ascending series of ethanol concentrations (2-10%) for up to 4 days per concentration. The amounts of ethanol and water consumed in 23-h sessions were measured. For CTA, a two-bottle procedure was employed. Distinctively flavoured solutions (saccharin or saline) were paired with IP injections of either ethanol (1.5 g/kg) or saline (1 ml/kg). Tests for aversion were made after two pairings, when both solutions were presented simultaneously for 10 min. At low concentrations of ethanol, drinking solution consumption was high, decreasing gradually with increasing concentrations; however, daily intake of orally self-administered ethanol remained stable. No significant differences could be established between the two groups tested. Ethanol preference [EtOH/EtOH + H2O] was attenuated in rats experienced with the CTA procedure before the OSA experiment. Injections of ethanol produced marked CTAs, even in rats that had consumed ethanol in the OSA experiment. The absence of tolerance to the aversive stimulus effects suggests that this stimulus property may not play a significant role in the consumption of ethanol.

Alcohol Drinking↗