Search PubMed⌕ Search

Biomedical subjects

R F Drewett

Publications and source records attributed to R F Drewett.

At least 55 records · Page 3Linked to original sources
PubMed1980

Testosterone-sensitive neurones respond to oestradiol but not to dihydrotestosterone.

Testosterone is aromatized to oestradiol in the brain, and it has been suggested that its effects on the brain are produced by this metabolite. Oestradiol does indeed restore sexual behaviour in castrated rats, but is is much more effective if combined with a second metabolite, dihydrotestosterone. This may be because the two hormones have a synergistic effect on the brain; or because the central effect of oestradiol synergises with the peripheral effects of dihydrotestosterone (which include stimulation of penile development). Evidence that the corticomedial amygdala (CMA) and the preoptic area of the rat brain are both involved in the control of sexual behaviour led us to examine the neurones of the stria terminalis that connect the two. These neurones are hormone-sensitive; their absolute refractory period is lengthened by castration and reduced again by testosterone. So we have investigated the aromatization hypothesis further by examining the effect of oestradiol and dihydrotestosterone on these testosterone-sensitive neurones. Oestradiol has exactly the same effect as testosterone; dihydrotestosterone has no effect, whether it is given alone or in combination with oestradiol.

Amygdala↗
PubMed1980

Effect of a traditional and of a new nipple shield on sucking patterns and milk flow.

The effect of a traditional (Mexican Hat) and of a new (Thin Latex) nipple shield on the sucking patterns and milk intake of 5-8-day-old babies was examined. Milk intake was determined accurately by test weighing using a Sartorius electronic balance with animal weighing keyboard, and sucking patterns by filming the mouth of the baby. The Mexican Hat reduced milk transfer by 58% (P is less than 0.01), and increased sucking rate (P is less than 0.05) and time spent resting (P is less than 0.01). The Thin Latex nipple shield reduced milk intake by a smaller amount (22%), and had no significant effect on sucking patterns.

Breast Feeding↗
PubMed1979

Testosterone reduces refractory period of stria terminalis neurons in the rat brain.

The absolute refractory period of neurons projecting from the corticomedial amygdala to the medial preoptic-anterior hypothalamic junction in rats was significantly increased by castration (from 1.01 to 1.61 milliseconds) and decreased again by testosterone (from 1.48 to 0.97 millisecond). Corticomedial amygdala neurons which projected to the capsule of the ventromedial nucleus of the hypothalamus were unaffected. These results demonstrate a specific, direct neuronal effect of testosterone.

Action Potentials↗
PubMed1979

The sexual attractiveness of male rats: olfactory and behavioral components.

Female rats are more attracted to intact than to castrated males. In this study, we compared the approach of female rats, in a straight runway, to (1) castrated males, which neither smell nor behave like intact males, (2) castrated males treated with dihydrotestosterone (DHT), which smell like intact males but behave like castrate males, and (3) castrated males treated with DHT and estradiol benzoate (EB), which both smell and behave like intact males. It was found that females ran faster to DHT males than to the castrate controls; and faster to the DHT-EB group than to the DHT group. Thus the odour and the sexual activity of male rats are independent effective sources of incentive to females.

Animals↗
PubMed1979

Sucking patterns of human babies on the breast.

Twenty-seven 5--8-day-old babies were filmed during normal breast feeding (one feed each). Sucking patterns were determined from the film from a total sample of 17,676 sucks. Intersuck interals fell on two distributions: one of intervals between sucks during bursts of sucking (1.3 sec and less), and the other of rests between bursts of sucking (1.3 to greater than 12 sec). As the milk flow dropped towards the end of the feed on each breast, the sucking rate within bursts increased (P less than 0.05), but there were more (P less than 0.001) and longer (P less than 0.001) rests between bursts of sucking. This study provides normative data on a normal population for use in studies of breast feeding.

Breast Feeding↗
PubMed1978

The milk ejection of the rat, as a stimulus and a response to the litter.

A finding that the milk ejection of the rat is stimulated effectively only if at least half the pups are suckled is confirmed. This relationship, however, is found if the mother is anaesthetized but not if the mother is conscious. If the mother is conscious, the milk obtained by individual hungry pups is unaffected by the number of other hungry pups suckled. This is true whether the other pups of the litter are removed, or whether they are present but satiated. After the milk ejection, pups tend to leave the mother's nipple. Milk yield decreases with each milk ejection of a series, but getting less milk does not make the pups more likely to leave the nipple in search of another.

Animal Population Groups↗
PubMed1977

Gonadal hormones and effects of partial reinforcement on appetitive behaviour in the rat.

Two experiments are reported in which rats were run in the straight alley with partial (PR) or continuous (CR) food reinforcement during acquisition and then extinguished. Hormone treatment (with estradiol benzoate, EB, or testosterone propionate, TP) was given during acquisition on both CR and PR schedules, but not during extinction. The results showed no effect of EB on the partial reinforcement extinction effect (PREE) in female rats. In males TP was found to reduce the PREE by differentially reducing resistance to extinction in the PR condition. Thus TP but not EB attenuates the behavioural effects of nonreward.

Animals↗
PubMed1975

Effects of neonatal castration and testosterone injection on adult open-field behaviour in rats with atypical sex difference in defecation.

In the open-field test, male rats usually defecate more and ambulate less than females. A strain was studied in which the males defecate less than females, while still ambulating less. Infants of this strain were castrated (males) or injected with testosterone propionate (females) and tested in the open field as adults. There were significant effects of these neonatal treatments on ambulation, but not on defecation, in contrast to previous reports for the latter measure in rats showing a sex difference in defecation taking the usual direction. It is suggested that absence of the usual direction of a sex difference normally under the developmental control of androgen may indicate a genotype which has escaped from such control. Finally, a number of 'sibling' effects' were observed, i.e. effects on the adult behaviour of the members of one sex in a litter produced by treatments administered in infancy to members of the other sex.

Animals↗
PubMed1975

Pattern of sucking in the infant rat during spontaneous milk ejection.

Two methods are described for measuring the sucking of rat pups on the nipples of the mother. The first uses pressure recording of the cannulated teatduct; the second uses direct observation of sucking behavior. Using these methods, the sucking behavior of the pups during sequences of milk ejections was investigated. Pressure recordings of the sucking of individual pups on the nipple showed that between milk ejections the pups sucked intermittently in bursts. During milk ejection itself there was a longer period of vigorous and continuous sucking. Behavioral observations on the level of sucking in whole litters of pups showed that the background bursts of sucking from the litter as a whole were randomly distributed in relation to the inferred time of oxytocin release. These results indicate that once the pups are sucking on the nipples, variations in the sucking behavior of the litter have no role in the timing of milk ejections in the mother.

Animals↗