Bernard Possidente

A time-less function for mouse Timeless

The timeless (tim) gene is essential for circadian clock function in Drosophila melanogaster. A putative mouse homolog, mTimeless (mTim), has been difficult to place in the circadian clock of mammals. Here we show that mTim is essential for embryonic development, but does not have substantiated circadian function.

Olfactory bulbectomy as a model for agitated hyposerotonergic depression.

Ablation of olfactory bulbs in rats reduced male sexual behavior, and altered the distribution of wheel-running activity between the light and dark phases of a 12:12 LD photoperiod. These effects were partially reversed by the tricyclic antidepressant amitriptyline. Olfactory bulbectomy also altered serotonin metabolism (5-HIAA/5-HT ratio) in the frontal cortex, nucleus accumbens, hippocampus and corpus striatum. These observations support the hypothesis that olfactory bulbectomy in rodents serves as a model of agitated hyposerotonergic depression.

QUANTITATIVE TRAIT LOCI (QTL) FOR CIRCADIAN RHYTHMS OF LOCOMOTOR ACTIVITY IN MICE

The loomotor activity of male mice (Mus musculus) was monitored by infrared photoelectric beams under three lighting regimens: LD (12 h of light and 12 h of dark), DD (constant dark), and LL (constant broad-spectrum light, 10 lux). Circadian period of locomotor activioty (τ) was compared among 3 inbred strains of mice, C57BL/6J (B6), BALB/c (C), and DBA/2J (D2), and 26 recombinant inbred strains B×D (B6×D2). the τ under both continuous low-intensity light and continuous darkenss varied significantly among strains. Under DD the mean τ was 23.8 h for B6, 23.7 h for D2, and 23.6 h for C. Under LL the mean τ was 25.1 for B6, 23.9 h for D2, and 25.5 h for C. Frequency histograms of the mean τ of 26B×D RI mouse strains (three to seven animals per strain) in either DD or LL and the difference between them, Δτ, had distributions which appeared unimodal, suggesting polygenic inheritances. The narrow-sense heritability determined using 26 strains of B×D RI mice was about 55% for τ and about 38% for both τ in LL and Δτ. An estimated four loci contribute to the variance of τ in constant darkness and five to the variance of τ in constant low-intensity light among the strains studied. Quantitative trait locus (QTL) analysis identified several potential genetic loci associated with τ in constant darkness, τ in constant low-intensity light, and Δτ. The associations of highest probability for each of these traits were theD1Nds4 locus (p<0.001) on mouse chromosome 1, theD5Ncvs52 locus (p<.05) on mouse chromosome 5, and thePmv12 locus (p<.01) at 70 cM on mouse chromosome 5, respectively. A QTL identified for τ was associated (p<.05) with theD2NDS1 marker at 45 cM on chromsome 2 near the Ea 6 marker at 46 cM associated (p<.05) with that reported for the period of wheel running activity in seven C×B RI strains (Schwartz, W. J., and Zimmerman, P.,J. Neurosci.10:3685 1990).

Olfactory bulb control of circadian activity rhythm in mice.

Ablation of mouse olfactory bulbs lengthened the circadian period of wheel-running activity by 43 min and delayed the onset of entrained activity by 108 min. A transient increase in activity during the light phase of the 12:12 h light-dark photoperiod also occurred following surgery. These disruptions suggest that olfactory systems can modulate mammalian circadian rhythms.

Aging lengthens circadian period for wheel-running activity in C57BL mice

Previous reports of age effects on circadian period in rodents show a slight shortening of period with age, with the exception of house mice (Mus domesticus) where a number of studies report mixed results. The present study consists of three comparisons of circadian period for wheel-running activity in young vs. older C57BL inbred mice following entrainment to 16:8 LD, 12:12 LD and 8:16 LD photoperiods. The free-running circadian period (tau(DD)) for wheel-running activity was significantly longer in older mice following entrainment to all three photoperiods. These results support a model of heterogeneous effects of aging on circadian period among different rodent species, and suggest that the lengthening of circadian period with age in house mice is not a function of age-dependent differences in after-effects imposed by prior entrainment.

Effects of anabolic androgenic steroids on the development and expression of running wheel activity and circadian rhythms in male rats

In humans, anabolic androgenic steroid (AAS) use has been associated with hyperactivity and disruption of circadian rhythmicity. We used an animal model to determine the impact of AAS on the development and expression of circadian function. Beginning on day 68 gonadally intact male rats received testosterone, nandrolone, or stanozolol via constant release pellets for 60 days; gonadally intact controls received vehicle pellets. Wheel running was recorded in a 12:12 LD cycle and constant dim red light (RR) before and after AAS implants. Post-AAS implant, circadian activity phase, period and mean level of wheel running wheel activity were compared to baseline measures. Post-AAS phase response to a light pulse at circadian time 15 h was also tested. To determine if AAS differentially affects steroid receptor coactivator (SRC) expression we measured SRC-1 and SRC-2 protein in brain. Running wheel activity was significantly elevated by testosterone, significantly depressed by nandrolone, and unaffected by stanozolol. None of the AAS altered measures of circadian rhythmicity or phase response. While SRC-1 was unaffected by AAS exposure, SRC-2 was decreased by testosterone in the hypothalamus. Activity levels, phase of peak activity and circadian period all changed over the course of development from puberty to adulthood. Development of activity was clearly modified by AAS exposure as testosterone significantly elevated activity levels and nandrolone significantly suppressed activity relative to controls. Thus, AAS exposure differentially affects both the magnitude and direction of developmental changes in activity levels depending in part on the chemical composition of the AAS.

Effects of withdrawal from anabolic androgenic steroids on aggression in adult male rats

In gonadally intact male rats, chronic exposure to high levels of testosterone propionate (TP) increases aggression, nandrolone (ND) has little effect and stanozolol (ST) suppresses aggression. The present experiment tested whether the effects of TP, ND and ST on aggression and reproductive tissues are reversed following anabolic androgenic steroid (AAS) withdrawal. Gonadally intact males received TP, ND, ST or vehicle for 12 weeks. Injections were then discontinued. Aggression was tested 3 weeks (short term) and 12 weeks (long term) after withdrawal of AAS treatment, with either a gonadally intact or a castrated opponent in three different environments (home, opponents and neutral cage). After short-term withdrawal, some parameters of aggression were significantly above control levels in TP males. There were no significant differences between ND or ST males and controls, though ST males showed the lowest levels of aggression. No significant differences between any of the groups were found after long-term withdrawal. Eighteen weeks after AAS withdrawal, serum testosterone (T) and LH levels were comparable to controls in all groups. Testes weights were at control levels in ST males, but significantly higher than controls in TP and ND males. Seminal vesicle weights were significantly elevated in TP males, but similar to controls in both ND and ST males. None of the prostate weights were significantly different from controls. These results suggest that aggression gradually returns to normal following withdrawal from AAS. Some, if not all, hormone levels and tissue weights return to normal, suggesting possible long-lasting effects of chronic AAS exposure.

Circadian period in mice: Analysis of genetic and maternal contributions to inbred strain differences

Differences of approximately 25 min in the free-running period of a circadian rhythm for wheel-running activity were observed among four inbred mouse strains (Mus musculus). Two sets of reciprocal hybrid crosses among the strains showed approximately intermediate values for circadian period in one cross and dominance for a short period in the other. Neither set of crosses showed evidence of significant maternal effects on circadian period. These results indicate that the inbred strain differences in circadian period are imposed primarily by direct effects of allelic differences among the strains, rather than through maternally mediated mechanisms.

Effects of fluoxetine and olfactory bulbectomy on mouse circadian activity rhythms

Olfactory bulbectomy (OBX) in SWR outbred male mice lengthened the free-running period and delayed the phase of a circadian rhythm for wheel-running activity. OBX also increased mean levels of activity. Two weeks of daily intraperitoneal injections of Fluoxetine (8 mg/kg), a serotonin re-uptake inhibitor, reversed the effects of bulbectomy on the mean level of activity and significantly shortened the free-running period of the activity rhythm. The phase of the activity rhythm was not significantly affected by the Fluoxetine treatment. These results are consistent with a hyposerotonergic mediation of the effects of OBX on circadian period and activity level.

Fluoxetine shortens circadian period for wheel running activity in mice.

Fluoxetine is a potent and specific serotonin re-uptake inhibitor and an effective antidepressant drug. Male mice were treated with either fluoxetine (8 mg/kg body weight per day) or saline. Wheel running activity was monitored for 2 weeks in a 12:12 LD cycle followed by 2 weeks in constant darkness (DD). Fluoxetine significantly shortened free-running circadian period for wheel running activity (23.93 +/- 0.08 h for fluoxetine treated mice versus 24.17 +/- 0.07 h for saline treated mice; p less than 0.03). These results are consistent with a role for serotonin in the regulation of circadian period in mice.