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Biomedical subjects

G A Davis

Publications and source records attributed to G A Davis.

At least 73 records · Page 4Linked to original sources
PubMed1978

Biphasic effects of the antiserotonergic methysergide on lordosis in rats.

As also reported by other workers, the antiserotonergic drug methysergide was found to facilitate lordotic responding in estrogen primed, ovariectomized rats. A second dose of methysergide 24 hr after the first, however, failed to produce any increment in responding. Animals received daily estrogen injections in order to maintain a relatively constant level of priming. After several days of methysergide, a progesterone injection facilitated lordosis to the same degree as in controls receiving only saline and estrogen. When a second injection of progesterone was given 24 hr later, however, the animals failed to respond. In contrast, saline controls with this estrogen paradigm responded equally well to both progesterone injections. These results are discussed in terms of their bearing on possible serotonergic and non-serotonergic mechanisms by which progesterone may control lordosis.

Animals↗
PubMed1978

Understanding indirect requests: an investigation of children's comprehension of pragmatic meanings.

Two experiments examined four-, five-, and six-year-old children's understanding of indirect requests. The experimental tasks required the children to judge the appropriateness of a listener's response to indirect requests involving an affirmative syntactic construction (Can you shut the door?), requests containing a negative element (Can't you answer the phone?), and requests for the state of affairs mentioned in the predicate to be changed (Must you play the piano?). Even the youngest age group exhibited an understanding of the first two types of indirect requests. However, only the six year olds showed any understanding of requests for a change in the state of affairs mentioned in the predicate. Possible factors responsible for children's difficulty with these requests are discussed.

Age Factors↗
PubMed1978

The response of adenosine 3',5'-monophosphate to norepinephrine in the hypothalamus and pineal organ of female rats in proestrus or diestrus.

The response of cAMP to norepinephrine (NE) was measured in hypothalamic tissue and pineal glands of cycling female rats killed on the mornings of proestrus and diestrus (in 4-day cycles) or diestrus II (in 5-day cycles). The results from 4- or 5-day cycles were similar in all cases. The report of Weiss and Crayton that the response of adenylate cyclase in pineal homogenates to NE is reduced on proestrus was confirmed, and a similar but lesser reduction was also detected with intact pineal glands incubated in vitro. Chopped hypothalamic tissue incubated in vitro revealed a greater response of cAMP levels to NE on proestrus compared to diestrus in the anterior hypothalamic-preoptic area, but no significant changes in the middle or posterior hypothalamus. In an effort to reproduce the changes noted on proestrus, ovariectomized animals were injected with estradiol benzoate for 2 days, but no effects of the treatment on the cAMP response to NE were found. If the animals were also given reserpine, however, the estrogen was effective in reducing the response of pineal adenylate cyclase to NE. Possible explanations for these results and the potential significance of alterations in NE receptor systems for the control of gonadotropin release are discussed.

Adenylyl Cyclases↗
PubMed1977

The influence of alpha-receptors on lordosis in the female rat.

The alpha-adrenergic agonist clonidine suppressed lordotic responding in spayed female rats brought into heat by estrogen and progesterone. The suppression was blocked by the alpha-antagonist yohimbine, but not by phenoxybenzamine or pimozide. The suppression was blocked by the alpha-antagonist yohimbine, but not by phenoxybenzamine or pimozide. Phenoxybenzamine itself had no suppressive effect on lordosis, though yohimbine did under some conditions. These results argue against an important facilitatory influence of norepinephrine on lordosis in the rat. Further, in comparison with the quite different findings recently reported from the guinea pig, they offer support for the presence of two different kinds of alpha-adrenergic receptors in the brain with different physiological functions.

Animals↗
PubMed1976

Pentobarbital inhibition of progesterone-induced behavioral estrus in ovariectomized guinea pigs.

Administration of pentobarbital inhibits the facilitatory effects of progesterone on the release of gonadotropins. In this experiment facilitatory effects of progesterone on lordosis behavior in guinea pigs were examined with pentobarbital anesthesia. Two major animal groups were subjects: one was short-term ovariectomized (2 weeks) and the other was long-term ovariectomized (several months). All animals received estradiol benzoate (6.6 mug s.c.) followed by progesterone (0.4 mg s.c.) 40 h later. Lordosis behavior was induced by the manual stimulation method of Young et al.29 Sodium pentobarbital (30 mg/kg) was injected 8,4 or 2 h before, simultaneously or 1, 2, 6, or 7 h after progesterone. Animals which received pentobarbital slept for 4.5-5 h with subsequent drowsiness for an additional 0.5-1 h. Pentobarbital injections given 8 h before progesterone had no effect on latency to the first lordosis or on other parameters of estrous behavior. However, pentobarbital delayed the onset of heat in estrogen treated ovariectomized guinea pigs when given 4 h before, 2 h before, or simultaneously with progesterone. The delay was directly related to the length of time the animals remained asleep after the progesterone injection, since estrous behavior was invariably displayed with the latency of controls after the animal awoke. Moreover, in animals which were awake for 1-2 h immediately after the progesterone injection before receiving pentobarbital, the latency of recovery from anesthesia to the first display of lordosis was about 1-1.5 h shorter than in the other pentobarbital groups. In contrast to the latency effects of pentobarbital, the duration of heat was unaffected by the anesthetic for all groups mentioned. In animals which received pentobarbital after they were already in heat, pentobarbital injection terminated heat and abolished it completely, since lordosis behavior was not displayed in the hours after recovery from anesthesia. Gross hypothalamic uptake of progesterone was not influenced by pentobarbital administration. Thus, it is tentatively concluded that an incubation period is necessary for progesterone to mediate the display of estrous behavior in the guinea pig in addition to the time necessary for neural uptake. The way in which pentobarbital interferes with the period of progesterone incubation is not currently known.

Animals↗
PubMed1976

Absence of hyperactivity in lead-exposed developing rats.

It has been reported that postnatal lead treatment produces hyperactivity in rodents. Using rats, we attempted to extend these findings. Locomotor activity of offspring of lead-intubated and pair-fed control mothers was measured at 24-27 days of age, and no significant differences in reactivity or basal activity were found. Observational scoring of the animals at 28-29 and 35-36 days of age indicated that active behaviors were slightly reduced in the lead-treated rats. The brain lead concentrations of experimental animals were slightly reduced in the lead-treated rats. The brain lead concentrations of experimental animals were significantly elevated over controls. Estimates of statistical power indicated that behavioral effects of the magnitude reported in the literature would likely have been detected. The present results indicate that low-level lead exposure may not reliably produce hyperactivity in rodents. A review of the literature suggests that other data provide little support for a recently proposed rodent model of hyperactivity in children.

Animals↗