Sex differences in performance in the Morris water maze and the effects of initial nonstationary hidden platform training.

Sex differences in rats' performance on a stationary hidden-platform task (spatial task) in the Morris water maze and the effects of initial nonstationary hidden platform training (NSP training) were examined. The NSP training was designed to familiarize rats with the general requirements of the water-maze task without providing spatial information. NSP training led to faster acquisition and improved retention of the subsequent spatial task in both males and females. There was a sex difference favoring males on acquisition and retention of the spatial task only in rats that had not received previous NSP training. Moreover, there was an apparent reversed sex difference favoring females on some measures of spatial performance in NSP-trained rats. These results suggest that performance on the water-maze task, including the expression of sex differences, can be altered by previous familiarization with nonspatial aspects of the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social learning of a food preference in male and female Mongolian gerbils is facilitated by the anxiolytic, chlordiazepoxide

Social transmission of a food preference in Mongolian gerbils (Meriones unguiculatus) depends on the presence of a social bond between the interacting animals. An "observer" gerbil can acquire a preference for a novel food item from a familiar and, or related "demonstrator" animal. However, exposure to an unfamiliar and unrelated demonstrator gerbil does not lead to acquisition of a food preference, even though the extent of social interaction and likelihood of transmission of food information is unaffected. Likewise, individual preexposure to a novel food does not affect diet preference in individual animals. Here we show that oral, nongavage, administration of the benzodiazepine anxiolytic, chlordiazcpoxide (CDP, 2.5, 5, and 10 mg/kg) has significant dose-associated differential facilitatory effects on social learning in male and female gerbils, while having no significant effects on either individual learning or total food consumption. These results suggest that the CDP mediated reduction of the anxiety associated with the interactions between unfamiliar/unrelated gerbils facilitates social learning. These findings also rise the possibility of sex differences in socially related anxiety and the effects of CDP on social learning in gerbils.     

Parasitized female mice display reduced aversive responses to the odours of infected males

The present study showed that parasites influence both the responses of uninfected females to males and the responses of female hosts to infected males. In female laboratory mice one of the consequences of exposure to the olfactory cues associated with an infected male was a reduction of the reactivity to a thermal surface, i.e. pain inhibition or analgaesia. Uninfected oestrous and non-oestrous female mice displayed marked analgaesic responses after exposure to the odours of males infected with either the enteric single-host nematode parasite, Heligmosomoides polygyrus, or the protozoan parasite, Eimeria vermiformis. The uninfected oestrous females distinguished between infected and physically stressed males, displaying a greater analgaesic response to the odours of infected males. These analgaesic responses and their anxiety/ fearfulness-associated behavioural correlates could elicit either a reduced interest in, or avoidance of, parasitized males by females. Oestrous female mice infected with H. polygyrus displayed a reduced analgaesic response to the odours of the infected males and differentially responded to the odours of males infected with either the same (H. polygyrus) or a different parasite (E. vermiformis). An exposure time of 1 min elicited minimal responses to the odours of males infected with the same parasite, H. polygyrus, and an attenuated, though significant, non-opioid peptide-mediated analgaesic response to males infected with E. vermiformis. An exposure time of 30 min elicited similar markedly reduced endogenous opioid peptide-mediated analgaesic responses to the odours of both of the categories of infected males. The responses to the odours of a stressed male were, however, unaffected by the parasitic infection. The reduced analgaesic responses of the parasitized females to the odours of infected males may involve either enhanced odour familiarity and responses to group odour templates and/or neuromodulatory shifts resulting in reduced fearfulness and potentially greater interest in the infected males.     

Analgesic responses of male mice exposed to the odors of parasitized females: Effects of male sexual experience and infection status.

The present study shows that parasites influence both the responses of males to infected females and the responses of male hosts to females. Male mice exposed for 30 min to the odors of females infected with the nematode parasite Heligmosomoides polygyrus displayed a naloxone-sensitive, opioid-mediated analgesia, whereas males exposed for 1 min showed a shorter duration and lower amplitude naloxone-insensitive "nonopioid" analgesia that involved serotoninergic (5-HT) and excitatory amino acid (N-methyl-D-aspartate [NMDA] receptor) systems. The male mice distinguished between the odors of infected and physically stressed females, displaying greater analgesia after exposure to the odors of infected than stressed females. The analgesic responses to the odors of infected females were also affected by the males' prior sexual experience; sexually experienced males exhibited significantly greater analgesia than sexually naive males. In contrast, male mice infected with H. polygyrus failed to show a nonopioid analgesia after exposure to the odors of infected females and displayed a markedly lower level of opioid analgesia than uninfected mice. These results show that male mice can discriminate between the odors of parasitized and nonparasitized females… (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of photoperiod and sex on lipopolysaccharide-induced hypoactivity and behavioral tolerance development in meadow voles (Microtus pennsylvanicus)

Lipopolysaccharide (LPS), the minimal immunogenic component of Gram-negative bacteria, is released during infection and causes a variety of sickness behaviors including decreased locomotor activity. This study considered how photoperiod and sex influence the effects of LPS in the meadow vole, Microtus pennsylvanicus. Male and female voles were housed under either reproductively stimulatory (long day: 16 h) or inhibitory (short day: 8 h) photoperiods. On Days 1 and 8, voles were injected with LPS (200 microg/kg, i.p.) or saline vehicle and locomotor activity was assessed 2 h later in an automated open field for 1 h. The first exposure to LPS caused significant decrements in locomotor activity in all LPS-treated groups, regardless of photoperiod or sex. On Day 8, both short day males and females exhibited behavioral tolerance to LPS, no longer displaying significant activity decrements. In contrast, long day females reinjected with LPS on Day 8 still exhibited significant hypoactivity on all locomotor measures. Similarly, long day males also appeared to exhibit a sustained expression of sickness behaviors on Day 8. In long day females, higher circulating progesterone levels were associated with an attenuated rate of tolerance formation to LPS. The present findings support the winter immunoenhancement hypothesis, which states that small mammals which undergo severe seasonal fluctuations undergo compromised immune functioning during the breeding season, and further indicate a potential role for progesterone in modulating these seasonal immune fluctuations in females.     

Learning to cope with biting flies: Rapid NMDA-mediated acquisition of conditioned analgesia.

A 30-min exposure to intact biting flies (stable flies) induced an opioid-mediated analgesia in fly-naive male deer mice, whereas exposure to either altered biting flies whose biting mouthparts were removed or nonbiting house flies had no significant effects. However, mice that were previously exposed to intact stable flies for 30 min exhibited significant analgesia when exposed 24–168 hr later to stable flies whose biting parts were removed, but not to nonbiting house flies. Administration of the specific N-methyl-D-aspartate (NMDA) antagonist NPC 12626 to fly-naive mice before exposure to intact flies, although not significantly reducing the analgesic response, blocked the subsequent conditioned analgesia. Naloxone, which blocked the intact biting fly-induced analgesia, did not alter the acquisition of the conditioned analgesic response to the altered stable flies. This demonstrates an NMDA-mediated acquisition of conditioned analgesia to a natural aversive stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of Repeated Exposure to Fox Odor on Locomotor Activity Levels and Spatial Movement Patterns in Breeding Male and Female Meadow Voles (Microtus pennsylvanicus)

Following five days of baseline activity recording, voles were exposed to fox odor for 3 min each day for five days. Immediately following each daily exposure, locomotor activity levels and spatial movement patterns were assessed using an automated activity monitoring system (Digiscan system). Males displayed a significant reduction in levels of various measures of locomotor activity following exposure to fox odor on each exposure day relative to baseline levels. Males preferred the corner of the testing box significantly more on the second day of fox odor exposure relative to baseline. Although females showed only a brief reduction in the number of movements made on the first day of odor exposure, this response lasted significantly longer on each of the subsequent odor exposure days. The reliability of the reductions in activity levels displayed across days by breeding male voles supports the hypothesis that this response is adaptive. Furthermore, the results suggest that, although female voles do not generally display this behavioral response, it can be elicited in females when the predation threat is repeated in consistent context.     

Learning from others to cope with biting flies: Social learning of fear-induced conditioned analgesia and active avoidance.

Although fear conditioning has received extensive attention, little is known about the roles of social learning whereby an individual may learn and acquire the fear responses of another. The authors examined individually and socially mediated acquisition of fear and analgesia to the natural aversive stimulus of biting flies. Exposure to biting flies elicited in individual naive mice analgesia and active self-burying to avoid the flies. When exposed 24 hr later to flies whose biting parts were removed, but not to nonbiting house flies, these mice displayed conditioned analgesia and self-burying. This "one-trial" conditioned analgesia and avoidance was also acquired through social learning without direct individual experience with biting flies. Naive "observer" mice that witnessed other "demonstrator" mice being attacked by biting flies exhibited analgesia and self-burying 24 hr later to altered flies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial learning and hippocampal volume in male deer mice: relations to age, testosterone and adrenal gland weight

Endoscopic carpal tunnel release is a controversial procedure used in the treatment of carpal tunnel syndrome. Although endoscopic carpal tunnel release is associated with less incisional pain and faster recovery time than the open carpal tunnel release, opponents of endoscopic carpal tunnel release suggest that its benefits are outweighed by its higher complication rates from median nerve transection and transient numbness of the fingers. Because of the huge economic and social impact of carpal tunnel syndrome in this country, we performed a cost-effectiveness analysis comparing endoscopic carpal tunnel release and open carpal tunnel release using guidelines established by the Panel on Cost-Effectiveness in Health and Medicine of the U.S. Public Health Service. A decision analytic model was used to measure differences in cost and effectiveness--expressed as quality-adjusted life-years (QALYs)--between endoscopic carpal tunnel release and open carpal tunnel release. The societal perspective was chosen, and probabilities for various outcomes for the two procedures were obtained from published randomized-controlled trials. Cost data were derived from the Medicare Resource-Based Relative Value Units published in the Federal Register. QALYs were obtained from two groups of health care providers using a utility-assessment questionnaire. Using probabilities for various outcomes from the two published randomized-controlled trials comparing endoscopic carpal tunnel release and open carpal tunnel release, we constructed a decision tree to derive both the cost and the QALYs for the two procedures. The incremental cost difference between endoscopic carpal tunnel release and open carpal tunnel release was $46, using Medicare cost and probabilities of various outcomes derived from a study by Brown et al. in 1993. We calculated QALYs for five age groups--25, 35, 45, 55, 65--assuming a life expectancy of 75 years. The marginal effectiveness (QALY of endoscopic carpal tunnel release minus QALY of open carpal tunnel release) ranged from 0.235 QALY for the 25-year-old age group to 0.066 QALY for the 65-year-old age group, giving a cost-effectiveness ratio of $195/QALY and $693/QALY, respectively. When compared with other accepted medical interventions such as breast cancer screening ($4836/QALY) and exercise to prevent coronary heart disease ($13,508/QALY), endoscopic carpal tunnel release seems to be cost-effective. However, our sensitivity analysis indicated that the cost-effectiveness ratio was very sensitive to a major complication such as median nerve injury. For endoscopic carpal tunnel release to be a cost-effective procedure, the incidence of median nerve injury must be one percentage point less for endoscopic carpal tunnel release than for open carpal tunnel release. Based on the data from the randomized-controlled trials, endoscopic carpal tunnel release seems to be a cost-effective procedure; however, before it can be recommended, greater emphasis must be given to the training of surgeons in this new technique, so that major complications such as median nerve injuries can be avoided. In addition, future studies must better define the actual incidence of nerve injuries for both endoscopic carpal tunnel release and open carpal tunnel release in the community setting.     

Sexually dimorphic aspects of spontaneous activity in meadow voles (Microtus pennsylvanicus): Effects of exposure to fox odor.

In this study, a multivariate analysis of the locomotor activity of adult, breeding male and female meadow voles (Microtus pennsylvanicus) was conducted. Overall, male voles made more movements and spent more time in the center of the activity chambers than did female voles. The authors further investigated the effects of brief exposure (3 min) to predator (red fox [Vulpes vulpes]) odor and various control odors (butyric acid, extract of orange) on subsequent activity. Control odors had no effects. Immediately following exposure to the fox odor, male voles exhibited significantly lower levels of activity and decreased center time. No significant changes in any activity variable were observed in the female voles following exposure to fox odor. This study provides evidence for sex differences in both basal activity levels of meadow voles and activity following exposure to a predator odor. (PsycINFO Database Record (c) 2010 APA, all rights reserved)