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Biomedical subjects

N G Forger

Publications and source records attributed to N G Forger.

32 records · Page 2Linked to original sources
PubMed1992

Differential effects of testosterone metabolites upon the size of sexually dimorphic motoneurons in adulthood.

This study examined the effect of testosterone and two of its metabolites on the size of motoneurons in the sexually dimorphic spinal nucleus of the bulbocavernosus (SNB) in adult male rats. Treatment of castrates with either testosterone or dihydrotestosterone maintained SNB cell size, although testosterone was more effective in this regard. However, estradiol, either alone or in conjunction with dihydrotestosterone treatment, had no effect on the size of the somata or nuclei of SNB motoneurons. These results indicate that testosterone affects SNB cell size by interacting with androgen receptors and that aromatized metabolites of testosterone are not involved in this aspect of motoneuronal plasticity in adulthood. Because the penile reflexes mediated by the SNB neuromuscular system are also sensitive to androgen but not estrogen treatment, morphological changes in SNB cells may contribute to the androgenic modulation of these reflexes.

Animals↗
PubMed1991

Sexual dimorphism and androgen effects on spinal motoneurons innervating the rat flexor digitorum brevis.

The foot muscle, flexor digitorum brevis, is innervated by motoneurons in the retrodorsolateral nucleus of the lumbar spinal cord in rats. We found this muscle to be sexually dimorphic, but insensitive to the anabolic or catabolic effects of androgen manipulation in adulthood: the flexor digitorum brevis was larger in adult male rats than in females, with no decrease in mass after castration in males nor any increase in size after androgen treatment of ovariectomized females. The cross-sectional area of motoneurons innervating this muscle was also sexually dimorphic, i.e., the motoneurons were larger in males. In contrast to the absence of an androgen effect on target muscle size, however, cross-sectional area of motoneurons decreased in adult males as a result of castration, and increased in adult females after androgen treatment. The dissociation of androgen effects on muscle mass and motoneuron size suggests the possibility of steroid effects upon motoneurons independent of effects upon target musculature.

Animals↗
PubMed1991

Does androgen affect axonal transport of cholera toxin HRP in spinal motoneurons?

We examined the effect of systemic androgen levels upon the rate at which lumbosacral motoneurons are labeled with cholera toxin-conjugated horseradish peroxidase (CT-HRP) injected into target muscles. CT-HRP first reaches the spinal nucleus of the bulbocavernosus between 8 and 10 h after injection into the bulbocavernosus muscle of adult male rats, but the number of motoneurons filled with CT-HRP does not differ between androgen-treated and control castrates at any of the time points examined. Thus, contrary to current speculation, we found no evidence that androgen can affect retrograde transport of CT-HRP by rat motoneurons.

Analysis of Variance↗
PubMed1988

Lipectomy influences white adipose tissue lipoprotein lipase activity and plasma triglyceride levels in ground squirrels.

Golden-mantled ground squirrels undergo marked fattening and fat depletion during the prehibernatory and hibernatory phases, respectively, of their annual body weight cycle. Fat regulation was studied by surgical removal (lipectomy) of most of the inguinal-subcutaneous, retroperitoneal, and parametrial fat depots from female squirrels during the weight-gain phase of the annual cycle. Seven weeks after surgery, body weights of lipectomized (Lipx) and Sham-Lipx squirrels were equivalent, although white adipose tissue was not completely recovered in Lipx animals. Lipoprotein lipase (LPL) activity was markedly elevated in subcutaneous adipose tissue of Lipx squirrels, but not in other depots. Plasma triglyceride (TG) levels also were higher in Lipx squirrels 7 weeks after surgery. Changes in LPL activity and plasma TG may contribute to body mass and lipid restoration following lipectomy.

Adipose Tissue↗
PubMed1987

Motoneuronal death during human fetal development.

The total number of ventral horn motoneurons throughout the spinal cord was determined for 19 human fetuses ranging in age from 11 to 32 menstrual weeks. There was a significant (approximately 35%) decline in motoneuron number between wks 11 and 25 of gestation, but no further decline from wks 25-32. Counts of pyknotic cells indicated a peak of motoneuronal degeneration between about wks 12 and 16 of age. The normal period of motoneuronal death observed here overlaps with the initiation of functional neuromuscular contact as well as the period of androgen production by the human fetal testes. As in rats, androgen may influence final motoneuron number in the human spinal cord by attenuating cell death in sexually dimorphic motor nuclei.

Cell Survival↗
PubMed1987

Seasonal variation in mammalian striated muscle mass and motoneuron morphology.

Feral white-footed mice are seasonal breeders that undergo predictable cycles of reproductive function. Photoperiod-induced fluctuations in gonadal function of white-footed mice were associated with morphological changes in perineal muscles and their motoneurons. Exposure to short daylengths resulted in testicular regression, decreased perineal muscle mass, and shrinkage of somata and nuclei of motoneurons of the spinal nucleus of the bulbocavernosus (SNB). These effects were reversed by reinstatement of long daylengths. Similar reductions in muscle mass and SNB soma size were seen following gonadectomy of white-footed mice. In addition, dendritic trees of SNB motoneurons were reduced in gonadectomized mice compared with dendritic arbors of intact mice or castrates provided with testosterone capsules. Androgen-mediated annual changes in muscle mass and motoneuron morphology appear to be a natural part of this species' physiology.

Animals↗
PubMed1986

Sexual dimorphism in human and canine spinal cord: role of early androgen.

Onuf's nucleus, located in the sacral spinal cord of dogs, cats, and primates, innervates perineal muscles involved in copulatory behavior. A sexual dimorphism in Onuf's nucleus was found in humans and dogs: males have significantly more motoneurons in this nucleus than do females. Prenatal androgen treatment of female dogs eliminated the dimorphism. In the homologous nucleus in rats, a similar effect of androgen has been shown to involve sparing of motoneurons from cell death. These results establish a morphological sex difference in a human central nervous system region of known function; well-studied animal models suggest explanations of the development of this dimorphism.

Animals↗
PubMed1986

Fat ablation and food restriction influence reproductive development and hibernation in ground squirrels.

The role of white adipose tissue in development of the reproductive apparatus of male golden-mantled ground squirrels was assessed by surgical removal of fat (lipectomy) immediately prior to onset of hibernation or by manipulation of fat levels through food restriction for 5 wk preceding hibernation. Animals then were maintained without food at 6 degrees C, and they hibernated from November 1983 until April 1984. At that time, blood plasma was assayed for hormone levels, and body mass, body composition, and masses of the testes and seminal vesicle-prostate complex were determined. At autopsy, testes and sexual accessory organs were heavier in Control squirrels than in Food-Restricted or Lipectomized (LIPX) animals. Paired-testes mass was positively correlated with body mass. Testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) levels were uniformly low in animals sampled during torpor, but were elevated in 2 animals that had regained the euthermic state. The Food-Restricted animals spent more time in torpor than did the other two groups, and the percentage of decrease in body mass over the hibernation season was less for Food-Restricted than for LIPX or Control animals. Adequate lipid stores may be essential for the normal development of the reproductive apparatus of male ground squirrels. In the field, animals with insufficient fat stores may forego reproduction and thereby conserve energy for survival.

Adipose Tissue↗
PubMed1985

Recovery of lipid mass after removal of adipose tissue in ground squirrels.

Male golden-mantled ground squirrels subjected to surgical removal of substantial portions of inguinal, retroperitoneal, and epididymal adipose tissue [lipectomy (Lipx)] or to sham lipectomy (Sham) during the early prehibernatory fattening phase did not differ in body mass 4 mo later at the time of their annual body weight peaks. Body mass restoration by Lipx squirrels was achieved without compensatory increases in food intake. There was little or no regeneration of epididymal adipose tissue, complete regeneration of the retroperitoneal depot, and an increase in mass of subcutaneous fat of Lipx animals. Epididymal and retroperitoneal adipocytes were equivalent in size in Sham and Lipx squirrels; adipocytes in subcutaneous fat were 20% larger in Lipx than in Sham animals. Generation of the annual body mass cycle of this ground squirrel involves active regulation of the lipid mass.

Adipose Tissue↗
PubMed1985

Photoperiodic regulation of reproductive development in male white-footed mice (Peromyscus leucopus) born at different phases of the breeding season.

Male white-footed mice were maintained from birth in chambers equipped with latitudinal timers programmed to simulate the natural progression of daylengths at 42 degrees N latitude. Mice were born into photoperiods starting on 1 April, 15 July, 15 September or 27 October. Testes and seminal vesicles of April- and July-born mice were mature at 60 days of age; puberty was delayed by several months in animals born into the September and October photoperiods but these mice became fecund at about 3.5 months of age, independent of current photoperiod. Therefore, increasing daylengths of late winter do not appear to synchronize the reproductive development of overwintering juveniles born at different times during the previous breeding season.

Animals↗
PubMed1984

Rapid recovery of body mass after surgical removal of adipose tissue in ground squirrels.

A substantial proportion of total adipose tissue mass was surgically removed from female ground squirrels during weight gain or weight loss phases of the circannual body weight cycle. Within 2 months of fat removal, squirrels had restored body mass to levels appropriate to the stage of the annual body weight cycle. These findings suggest that ground squirrels may use feedback from body lipids in controlling body weight.

Acclimatization↗
PubMed1983

Rhythms of barbiturate-induced sleep time in deermice entrained to non-twenty-four hour photocycles.

The present experiment examined whether entrainment to twenty-four hour days is advantageous for physiological and behavioral adaptations to a pharmacological challenge. Adult, male deermice (Peromyscus maniculatus) were injected with sodium pentobarbital at 8.5, 14.5, 20.5, 2.5 and again at 8.5 hr after light onset while entrained to a 24 hr day (light/dark (LD) 14:10). Time to recover from anesthesia was recorded. Subsequently, the dark phase of the LD cycle was reduced 15-20 min every 10 days until a 23 hr photocycle was achieved, (LD 14:9; T = 23 hr). Injections of sodium pentobarbital were again administered at 8.5, 14.5, 20.5 and 2.5 hr after light onset and sleep times recorded. This procedure was repeated at T = 21 hr (LD 14:7) and T = 18 hr (LD 14:4). A variation in sleep time was observed during entrainment to all T-cycles except T = 18 hr. Sleep time after drug administration was generally longer during the light than during the dark phase of each photocycle. Recovery from anesthesia was not compromised in mice entrained to photocycles with periods of 23 or 21 hr; however, entrainment to very short days disrupted the normal pattern of response to barbiturate administration. Entrainment to a range of daylengths that deviate appreciably from 24 hr is consistent with normal physiological function.

Animals↗
PubMed1982

Reproductive state modulates ethanol intake in rats: effects of ovariectomy, ethanol concentration, estrous cycle and pregnancy.

Intact adult female rats had a greater preference for a 4% (v/v) ethanol solution than ovariectomized (OVX) rats in a two-tube preference situation. This preference difference was not particular to the 4% concentration, but was exhibited for solutions ranging from 1-9% ethanol. OVX animals reached peak preference at weaker ethanol concentrations than did control animals, while the volume of absolute ethanol consumed by each group was high dependent on the concentration of ethanol offered. OVX, but not intact, rats showed a strong positive correlation between alcohol preference and preference for a saccharine solution. Pregnant and lactating rats exhibited depressed preference for 4% ethanol. Preference returned to control levels following weaning. Ethanol intake and preference varied systematically over the four-day estrous cycle, being lowest on the day of proestrus.

Alcohol Drinking↗