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Biomedical subjects

D R Weaver

Publications and source records attributed to D R Weaver.

83 records · Page 5Linked to original sources
PubMed1987

The circadian-gated timing of birth in rats: disruption by maternal SCN lesions or by removal of the fetal brain.

The roles of the maternal suprachiasmatic nuclei (SCN) and fetal brain in the circadian-gated timing of birth were studied in rats. The circadian gating of birth was shown by exposing different groups of dams to lighting cycles of opposite phase during pregnancy. Regardless of the phase of the prenatal lighting cycle, the time of birth was gated over a 36-h temporal window so that most births occurred during subjective day. Destruction of the maternal SCN eliminated the circadian gating; births occurred in a single distribution that peaked in the middle of the 36-h window. Removal of the fetal brain also disrupted the circadian gating of birth; dams of brain-aspirated fetuses no longer exhibited a daytime preference for births. These results show that the maternal SCN are necessary for the normal circadian gating of birth and are also consistent with a role for the fetal brain in this process.

Age Factors↗
PubMed1987

Nicotinic cholinergic influences on sexual receptivity in female rats.

Drugs which alter nicotinic cholinergic transmission were administered to female rats to examine the neurochemical regulation of feminine sexual behavior. Nicotine (50, 100 or 200 micrograms/kg, IP) facilitated lordosis behavior 5 minutes after injection in estrogen-primed ovariectomized (OVX) rats. Pretreatment with the nicotinic antagonist, mecamylamine (MECA, 2.5 or 10 mg/kg) prevented this effect, while atropine pretreatment (30 mg/kg) reduced it. Mecamylamine pretreatment also reduced lordotic behavior induced by bilateral intracerebroventricular (ICV) injection of the cholinesterase inhibitor, eserine (5 micrograms/cannula). However, MECA treatment (5 or 10 micrograms/cannula, bilaterally, ICV, or 5 or 10 mg/kg, IP) did not reduce sexual receptivity in OVX rats made highly receptive with estrogen plus progesterone priming. By comparison with previously published results, MECA is apparently less effective than muscarinic antagonists in disrupting sexual receptivity in several paradigms. There appears to be a critical muscarinic link in the neural circuit for sexual receptivity, but there does not appear to be a comparable nicotinic link. In fact, the lordosis-facilitating effect of nicotine may be a pharmacological effect unrelated to the normal neurochemical regulation of sexual receptivity.

Animals↗
PubMed1987

Maternal-fetal communication of circadian phase in a precocious rodent, the spiny mouse.

The development of circadian rhythms was examined in a precocious rodent species, the spiny mouse. Spiny mouse pups born and reared in constant darkness expressed robust circadian rhythms in locomotor activity as early as day 5 of life. Free-running activity rhythms of pups born and reared in constant darkness were coordinated with the dam on the day of birth. Postnatal maternal influences on pup rhythmicity are minimal in this species, as pups fostered on the day of birth to dams whose circadian phases were opposite to the pups' original dams were coordinated with their original dams on the day of birth. Studies using 2-deoxy-D-[1-14C]-glucose autoradiography showed that there were synchronous (coordinated) rhythms in metabolic activity in the maternal and fetal suprachiasmatic nuclei, directly demonstrating prenatal coordination of maternal and fetal rhythmicity. Maternal-fetal coordination of circadian phase was not the result of direct entrainment of the fetuses to the environmental light-dark cycle. These results demonstrate that there is prenatal communication of circadian phase in this precocious species, without demonstrable postnatal maternal influences on pup circadian rhythmicity. Spiny mice therefore represent an important animal model in which circadian rhythms in the postnatal period can be used to precisely assess prenatal influences on circadian phase.

Animals↗
PubMed1987

Definition of a prenatal sensitive period for maternal-fetal communication of day length.

The duration of the nocturnal elevation of melatonin in the dam is a key feature in providing the Djungarian hamster fetus with a prenatal photoperiodic history. The developing animal compares the prenatal photoperiod with the photoperiod experienced during the postnatal period to properly time puberty. In the present report, we define the period during gestation when melatonin administered to the dam is effective in providing the fetus with a prenatal photoperiodic history. The administration of melatonin (50 ng delivered over 10 h at night) by timed infusions to pregnant, pinealectomized Djungarian hamsters for the last 4-7 days of gestation stimulated testicular weights of male pups reared in 14 h of light/day. Single 10-h melatonin infusions were ineffective in stimulating reproductive development (testes weights on day 34) of the male pups, irrespective of the gestational age of the fetus at the time of treatment. In contrast, two consecutive nightly 10-h infusions during gestation clearly stimulated testicular development. The gestational age of the fetus at the time of infusion strongly influenced the response, however. Treatments beginning between 6 and 3 days before birth were effective in stimulating postnatal reproductive development of the offspring. These results indicate that there is a well-delineated, sensitive period during prenatal development when melatonin can provide the fetus with a prenatal photoperiodic history.

Age Factors↗
PubMed1986

Maternal melatonin communicates daylength to the fetus in Djungarian hamsters.

Daylength (photoperiod) influences the rate of reproductive development in the juveniles of some photoperiodic species. Recent studies show that daylength during the prenatal period is perceived by the fetus and that this perception can profoundly influence postnatal reproductive and somatic development. Using the photoperiodic Djungarian hamster, we assessed the role of the maternal pineal gland and its hormone, melatonin, in this prenatal perception of daylength. Maternal pinealectomy eliminated the influence of prenatal photoperiod on testicular and body weights of male pups, suggesting that a product from the maternal pineal gland communicates daylength to the fetus. Infusion of the pineal hormone melatonin into pinealectomized dams for various durations during gestation mimicked the effect of varying the prenatal photoperiod on both testicular and body weights. These results indicate that pineal melatonin is involved in this novel form of communication from mother to fetus.

Animals↗
PubMed1982

Alteration of muscarinic binding in specific brain areas following estrogen treatment.

Systemic administration of estradiol benzoate (EB) to ovariectomized female rats significantly altered cholinergic muscarinic binding of [3H]quinuclidinyl benzilate in discrete brain regions. Specifically, EB increased muscarinic binding in the medial basal hypothalamus (MBH) and decreased muscarinic binding in the medial preoptic area (POA). These alterations were dose-dependent and appeared to reflect changes in the number of muscarinic binding sites. Treatment with EB failed to significantly affect binding in several control areas in females or in the MBH and POA of males.

Amygdala↗