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Biomedical subjects

T G Baker

Publications and source records attributed to T G Baker.

At least 55 records · Page 3Linked to original sources
PubMed1975

A comparison of the discriminative stimulus properties of R-2,5-dimethoxy-4-methylamphetamine (R-DOM) and S-amphetamine in the rat.

The effects of 0.75 mg/kg of R-DOM and 1.0 mg/kg of S-amphetamine served as discriminative stimuli in the control of a two-lever discrimination response. Dose-response evaluation of the two agents indicated that in S-amphetamine-trained animals the drug effects produced by test doses of 0.5 to 2.2 mg/kg of S-amphetamine could be considered as a dose-dependent continuum of low to high stimulus intensity. In R-DOM trained subjects, low to moderate doses of R-DOM (0.5-1.5 mg/kg) produced dose-related discriminative responding, but the high dose of R-DOM (2.2 mg/kg) resulted in random responding. When animals trained to discriminate 1.0 mg/kg of S-amphetamine from saline were given 0.5 or 0.75 mg/kg of R-DOM, they tended to respond on the drug correct lever. However, higher doses of R-DOM (1.5 and 2.2 mg/kg) produced random responding. Similarly, animals trained to discriminate 0.75 mg/kg of R-DOM from saline exhibited correct responses following 0.5 and 0.75 mg/kg of S-amphetamine, but not after 1.5 and 2.2 mg/kg. These data suggest that low doses of R-DOM produce discriminative stimuli that are qualitatively different from those of higher doses. Stimuli following low doses of R-DOM also appear similar in some respects to those following low doses of S-amphetamine.

DOM 2,5-Dimethoxy-4-Methylamphetamine↗
PubMed1975

Behavioral and neuropharmacological analysis of amphetamine and 2,5-dimethoxy-4-methylamphetamine in rats.

A comparison of the behavioral pharmacology of DOM and amphetamine in rats indicated that lower doses (0.10-1.0 mg/kg) of the two agents had similar effects on schedule-controlled food-reinforced and shock-avoidance behavior. Similarities were also noted in their effects on horizontally directed motor activity when testing was preceeded by a period of acclimation. However, most doses of DOM tended to decrease unacclimated motor activity, while amphetamine increased this behavior. Neuropharmacological antagonism studies indicated that brain catecholamines (CA) and serotonin (5-HT) are involved in the behavioral effects of both DOM and amphetamine. Cinanserin, a 5-HT receptor blocker, attenuated the behavioral disruptive effects of both agents on food-reinforced responding. Cinanserin attenuated the effects of all doses of DOM and those of higher doses of amphetamine on shock avoidance. When given prior to lower doses of amphetamine, there was a greater behavioral stimulation than when amphetamine was given alone. Prior depletion of brain CA with alpha-methyltyrosine (alpha-MT) did not affect DOM induced disruption of food-reinforced responding, while alpha-MT attenuated the behavioral effects of all doses of DOM and amphetamine on shock avoidance. These data suggest that DOM and amphetamine share a similar component in their mechanism of action which depends on the availability of a releasable pool of brain CA.

DOM 2,5-Dimethoxy-4-Methylamphetamine↗
PubMed1975

Relationship between the secretion of the corpus luteum and the length of the follicular phase of the ovarian cycle.

The variation in the length of the follicular phase in many mammals may be related to the cellular origin of oestradiol secreted during the luteal phase. In all species the time taken for a small developing follicle (4-5 layers of granulosa cells) to mature to a preovulatory follicle may be the same as that which has been found experimentally in the mouse (10-17 days). In animals such as the sheep, in which there is no source of oestradiol other than the Graafian follicle, follicular development proceeds unimpaired throughout the luteal phase, and the 'follicular phse' which involves only the final stages of maturation of the Graafian follicle is relatively short. In primates, however, in which there is an extrafollicular source of oestrogen from the CL, the secretion of gonadotrophins is suppressed during each luteal phase to a level too low to initiate and maintain follicular development. At the end of each luteal phase and the beginning of the subsequent follicular phase, therefore, it is necessary to initiate the growth of a new crop of small follicles. The time taken for these follicles to develop inot preovulatory follicles determines the length of the follicular phase.

Animals↗
PubMed1975

Influence of prostaglandins and human chorionic gonadotrophin on progesterone concentration and oocyte maturation in mouse ovarian follicles maintained in organ culture.

The response of mouse ovaries maintained in organ culture to prostaglandin E-2 (PGE2) and prostaglandin F-2alpha (F2alpha) was assessed using quantitative histological and radioimmunoassay procedures. Prostaglandin E2 induced histological changes in the cultured follicles comparable to those induced by human chorionic gonadotrophin (HCG) and the increase in the number of oocytes undergoing preovulatory maturation over the control value was the same irrespective of the treatment (PGE2 alone, HCG alone, or PGE2+HCG). The amount of progesterone/ml of culture medium was also significantly higher with these preparations than in control cultures (about 125 ng/ml compared with 57 ng/ml). By contrast, 5 mug PGF2alpha/ml medium increased neither the number of oocytes undergoing maturation nor the concentration of progesterone in the culture medium. The latter increased when the dose of PGF2alpha was increased to 30 mug/ml, although the proportion of oocytes beyond the dictyate stage remained at the control level. There was no augmentation in the response (above the level for HCG alone) when HCG and PGF2alpha were added to the explant medium simultaneously. These results are discussed in terms of the possible mechanism of action of the various preparations.

Animals↗
PubMed1975

Response of mouse graafian follicles in organ culture to varying doses of follicle-stimulating hormone and luteinizing hormone.

The response of mouse ovaries maintained in organ culture to follicle-stimulating hormone (FSH), LUTEINIZING HORMONE (LH) and human chorionic gonadotrophin (HCG) was assessed using quantitative histological and radioimmunoassay techniques. In terms of the induction of preovulatory maturation in follicular oocytes, 1 mugFSH/ml medium was as effective as 10 mugLH/ml. The lowest doses of HCG and LH used (0.2 i.u./ml and 1 mug/ml respectively) had no effect on oocyte maturation, whereas the response to FSH WAS VIRTUALLY UNCHANGED IRRESPECTIVE OF DOSE (1-10 MUG/ML). When the level of progesterone in the medium at the end of organ culture was used as an index of ovarian response, LH was more effective than FSH and HCG, although all the hormones induced a significant increase, irrespective of dose. These results are discussed in terms of the mode of action of gonadotrophins in the processes culminating in ovulation.

Animals↗