Biomedical subjects

M Kavaliers

Publications and source records attributed to M Kavaliers.

At least 37 records · Page 2Linked to original sources

PubMed2000

Influence of a natural stressor (predator odor) on locomotor activity in the meadow vole (Microtus pennsylvanicus): modulation by sex, reproductive condition and gonadal hormones.

Sex differences in a variety of non-reproductive behaviors have been indicated to occur in seasonally breeding polygynous promiscuous rodents such as the meadow vole, Microtus pennsylvanicus. The present study was designed to assess the effects of reproductive and hormonal status on the locomotor responses of meadow voles following brief exposure to the odors of a natural predator, the Red fox (Vulpes vulpes). Adult male and female meadow voles, which are seasonal photoperiodically-induced breeders, were housed in either mixed sex pairs under a long, reproductively stimulatory photoperiod (simulating breeding: long light cycle, paired: LLC + P) or in same-sex pairs under a short, reproductively inhibitory photoperiod (simulated non-breeding: short light cycle, non-paired: SLC-NP). On 2 consecutive days following 1 day of baseline activity monitoring, voles were exposed individually for 3 min to fox odor and a novel pungent control odor (extract of almond). The levels of various measures of activity that were displayed by the voles were assessed by an automated Digiscan activity monitoring system. LLC + P (simulated breeding) voles displayed higher basal levels of activity relative to SLC + NP (simulated non-breeding) voles, with males displaying greater activity than females. LLC + P (simulated breeding) males displayed a significant reduction in activity levels following exposure to fox odor relative to control odor. The reductions in activity following fox odor exposure were related to plasma testosterone levels such that a larger behavioral response (i.e. greater reduction) was associated with higher levels of testosterone. Furthermore, dividing males into high and low testosterone groups based on the median levels of testosterone revealed that high but not low testosterone males displayed reductions in activity following exposure to fox odor relative to control odor. No changes in activity levels following exposure to fox odor were noted in SLC-NP males, and either SLC-NP or LLC + P females. These results show that this sexually dimorphic non-reproductive behavior is significantly influenced by reproductive condition and gonadal hormone levels.

Animals↗

PubMed1999

Repeated injections of lipopolysaccharide attenuate the satiety effects of cholecystokinin.

The present study examined the effects of repeated injections of lipopolysaccharide (LPS) and cholecystokinin (CCK) on both sucrose palatability and body weight. Rats received repeated injections of LPS (200 microg/kg), CCK (8 microg/kg) and/or NaCl on days 1, 4, 7 and 10. Body weight was monitored on each test day and sucrose palatability was assessed using the taste reactivity test (TRT) on days 7 and 10. Rats treated with LPS developed a rapid tolerance to the reductions in body weight; however, this tolerance did not affect sucrose palatability. Furthermore it was found that repeated exposures to LPS and CCK attenuated the typical satiety related behaviors produced in the TRT by administration of CCK. This desensitization to CCK with repeated exposures to LPS may be one of the mechanisms that could account for the rapid development of tolerance to LPS-induced hypophagia.

Animals↗

PubMed1999

Light-dependent effects of magnetic fields on nitric oxide activation in the land snail.

The attenuation of opioid analgaesia is a well established effect of extremely low frequency (ELF) magnetic fields with light having a modulatory role in these effects such that when the ELF exposures are carried out in the dark, the inhibitory effects on analgesia are reduced. Here, we considered the light dependency of the effects of exposure to an ELF magnetic field prior to the induction of opioid analgesia. Brief exposure to a 60 Hz field potentiated in a light dependent manner the inhibitory effects of the nitric oxide (NO) precursor L-arginine on the level of subsequent opioid-induced analgesia in the land snail Cepaea nemoralis. This suggests a general light dependency of the actions of magnetic fields and the involvement of NO in the mediation of the effects of magnetic fields.

Analgesics↗

PubMed1999

Brief predator odour exposure activates the HPA axis independent of locomotor changes.

Although predator exposure has been proposed to elicit both behavioural responses and neuroendocrine effects in rodents, results of an increasing number studies have failed to consistently detect both of these alterations. We provide a detailed multivariate quantitative assessment of locomotor activity levels and plasma levels of adrenocorticotrophic hormone (ACTH) and corticosterone of male and female laboratory rats following brief (5 min) exposure to a predator odour, (2-propylthietane, the main constituent of weasel anal gland secretion). We show that there is a clear distinction between the behavioural and neuroendocrine responses, with predator odour inducing significant increases in corticosterone and ACTH levels without any significant accompanying changes in various locomotor activity measures.

Adrenocorticotropic Hormone↗

PubMed1999

Relations of hippocampal volume and dentate gyrus width to gonadal hormone levels in male and female meadow voles.

The present study examined hippocampal volume and dentate gyrus width and their relations to gonadal hormone levels in adult male and female meadow voles, Microtus pennsylvanicus. Females were split into High and Low Estradiol groups based on the median estradiol level. Males were similarly split into High and Low Testosterone groups. Contrary to previous reports in wild meadow voles, there was no evidence of an overall sex difference in hippocampal volume. However, when male-female comparisons were limited to High Testosterone males and Low Estradiol females a significant sex difference in hippocampal volume favouring males did emerge. Hippocampal volume in males was related to testosterone level, with High Testosterone males having significantly larger hippocampi than Low Testosterone males. Similarly, there was a significant influence of plasma estradiol level on hippocampal volume and left dentate gyrus width, with High Estradiol females having larger hippocampi and dentate gyrus width than Low Estradiol females. In addition, consistent with previous findings in the laboratory rat, there were sex differences favouring males in right dentate gyrus width. These findings show that there is a complex relationship between hippocampal volume, dentate gyrus width and gonadal hormone levels in male and female meadow voles.

Animals↗

PubMed1999

Social learning in animals: sex differences and neurobiological analysis.

Social learning where an "individual's behavior is influenced by observation of, or interaction with, another animal or its products" has been extensively documented in a broad variety of species, including humans. Social learning occurs within the complex framework of an animal's social interactions that are markedly affected by factors such as dominance hierarchies, family bonds, age, and sex of the interacting individuals. Moreover, it is clear that social learning is influenced not only by important sexually dimorphic social constraints but also that it involves attention, motivational, and perceptual mechanisms, all of which exhibit substantial male-female differences. Although sex differences have been demonstrated in a wide range of cognitive and behavioral processes, investigations of male-female differences in social learning and its neurobiological substrates have been largely neglected. As such, sex differences in social learning and its neurobiological substrates merit increased attention. This review briefly considers various aspects of the study of social learning in mammals, and indicates where male-female differences have either been described, neglected and, or could have a potential impact. It also describes the results of neurobiological investigations of social learning and considers the relevance of these findings to other sexually dimorphic cognitive processes.

Animals↗

PubMed1999

Parasites and behavior: an ethopharmacological analysis and biomedical implications.

Parasites and disease are increasingly recognized as agents of behavioral, ecological and evolutionary importance having a variety of influences on their hosts other than the more obvious pathological and immunological changes. Parasites can have significant behavioral effects even when parasitism is sub-clinical with these effects proposed to either benefit the parasite (parasite 'manipulation'), benefit the host, or to simply arise as side-effects of the infection (parasitic 'constraints'). However, until relatively recently little attention has been paid to the neuromodulatory substrates that mediate these behavioral changes. Ethopharmacology incorporates an evolutionary approach to the study of behavior with pharmacological analysis of neuromodulatory mechanisms. As such, this approach is appropriate for, and has been applied to, the analysis of the effects of ectoparasites (e.g. biting and blood-feeding flies) and endoparasites (e.g. protozoa, nematodes) on a number of behaviors (e.g. pain inhibition, learning and memory, responses to predators and anxiety, mate selection) in selected host-parasite systems. Ethopharmacology suggests a promising direction by which neuromodulatory mechanisms that underlie the effects of parasites on behavior, including that of humans, can be addressed.

Animals↗

PubMed1999

Differential effects of lipopolysaccharide and cholecystokinin on sucrose intake and palatability.

The differential effects of CCK and lipopolysaccharide (LPS) on sucrose intake and palatability were examined. Rats were injected with LPS (200 microg/kg ip) or NaCl (0.9%, vehicle) and 2 h later received a second injection of either CCK (8 microg/kg ip) or NaCl. In experiment 1, sucrose (0.3 M) intake was monitored for 1 h on three different test days 72 h apart, while in experiment 2, palatability was assessed by means of the taste reactivity test (TRT) on two separate days (72 h apart). In the TRT, orofacial and somatic responses to brief (30 s) intraoral infusions of sucrose were recorded and analyzed for response frequency. Singly, LPS and CCK reduced sucrose intake, with a more pronounced effect from combined LPS and CCK. LPS by itself did not alter sucrose palatability, as evidenced by continuous high levels of ingestive responding. In contrast, CCK-treated rats displayed a pattern of responding indicative of satiety, as did the combined LPS-CCK-treated rats. These results suggest that LPS does not induce hypophagia by altering palatability.

Animals↗

PubMed1999

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.

Adaptation, Physiological↗

PubMed1998

Brief exposure of mice to 60 Hz magnetic fields reduces the analgesic effects of the neuroactive steroid, 3alpha-hydroxy-4-pregnen-20-one.

Relatively weak, extremely low frequency (ELF), magnetic fields have been shown to exert a variety of biological effects, although the modes of action remain to be established. Neuroactive steroids and neurosteroids have been shown to produce a diverse range of rapid centrally mediated behavioral and physiological effects that are reported to be sensitive to magnetic fields. Here we show that brief exposure of male mice to an ELF magnetic field (30 min, 60 Hz, 141 microT peak) significantly reduces the analgesic effects arising from intracerebroventricular (i.c.v.) administration of the centrally produced allylic neuroactive steroid, 3alpha-hydroxy-4-pregnen-20-one (3alphaHP) and that the dihydropyridine (DHP) calcium channel antagonists, diltiazem and nifedipine, block the inhibitory effects of the 60 Hz ELF on 3alphaHP-induced analgesia. These results indicate that exposure to 60 Hz ELF affects the analgesic effects of neuroactive steroids such as 3alphaHP through alterations in calcium channel function. These findings raise the possibility that ELF magnetic fields may, in part, exert their actions through effects on diverse neuroactive steroid modulated processes.

20-alpha-Dihydroprogesterone↗

PubMed1998

Individual differences in radial maze performance and locomotor activity in the meadow vole, Microtus pennsylvanicus.

Individual differences in the radial maze performance and locomotor activity of wild-caught and first-generation laboratory-born meadow voles are described. Based on their patterns of response in an eight-arm radial maze the essentially wild voles fell into three behavioral categories: 1) strict algorithmic (i.e., they systematically chose the next adjacent arm to their previous choice); 2) nonalgorithmic (i.e., they ran the maze without any consistent or definable pattern); and 3) nonrunners (i.e., nonperformers of the task who remained relatively immobile in the arms of the maze). The algorithmic and nonalgorithmic voles further differed in their responses to an interference manipulation of the radial maze task. Algorithmic individuals displayed a marked performance deficit, while the nonalgorithmic individuals showed minimal disruption to a 1-min delay interruption of the maze task. Measurements of several aspects of locomotor activity using the automated Digiscan activity monitoring system revealed that the algorithmic individuals also displayed significantly greater levels of activity than the nonalgorithmic or nonrunners, with no significant difference in activity between the latter two groups. These findings suggest that the algorithmic voles were relatively inflexible in their behavior, while the nonalgorithmic individuals were more flexible in their maze performance and likely in their use of spatial and nonspatial information. These individual differences in laboratory measures of learning behavior and locomotor activity in meadow voles are consistent with the polymorphism that is proposed to occur in the wild.

Animals↗

PubMed1998

Sex differences in spontaneous locomotor activity and rotational behavior in meadow voles.

Sex differences in rotational behavior have been most clearly established in laboratory rats with females exhibiting a turning bias. Here, using an automated open-field apparatus, locomotor activity and spontaneous rotational behavior were examined in diurnally crepuscularly active reproductive male and female meadow voles (Microtus pennsylvanicus). Meadow voles, being induced ovulators, permitted analysis of females in constant behavioral estrous. Males displayed significantly greater levels of activity and also significantly greater levels of clockwise but not counterclockwise rotational behavior relative to the females. Rotational behavior was less strongly related to activity levels in female as compared to male voles. In addition, females displayed an overall turning bias. These results contrast with findings from laboratory rats in which females are reported to display greater levels of both locomotor activity and rotational behavior. They are, however, consistent with the rotational bias evident in female rats. The present findings confirm the presence of sex differences in rotational behavior and indicate that factors other than activity levels are involved in the generation and/or expression of these sex differences. Sex differences in anxiety and routine-like behavior (i.e., asymmetry in movement) are discussed as possible factors contributing to these male-female differences in rotational behavior.

Animals↗

PubMed1998

Sex differences in spatial learning and prefrontal and parietal cortical dendritic morphology in the meadow vole, Microtus pennsylvanicus.

The prefrontal and parietal cortex has been implicated in the mediation of spatially related behaviors in male and female laboratory rats. Meadow voles, Microtus pennsylvanicus, are diurnally-crepuscularly active microtine rodents that exhibit a variety of sexually dimorphic spatially associated behaviors in both the laboratory and wild. In the present study we examined both the spatial Morris water maze performance and dendritic architecture and branching of neuronal cells in the prefrontal and parietal cortex of reproductive male and female meadow voles. Males learned the location of the hidden platform in the water task faster than estrous females and on probe trials they spent more time in the previously correct quadrant than females. Dendritic analysis with Golgi-Cox stained sections showed that male voles had significantly more dendritic arborization in the medial prefrontal and parietal cortex than females. These sex differences in both spatial navigation ability and in neural structures related to spatial navigation in meadow voles suggest that the size of neural areas might be shaped by ecological pressures associated with sexually dimorphic spatial behaviors.

Animals↗

PubMed1998

Evidence for the involvement of nitric oxide and nitric oxide synthase in the modulation of opioid-induced antinociception and the inhibitory effects of exposure to 60-Hz magnetic fields in the land snail.

The attenuation of opioid peptide-mediated antinociception is a well-established effect of extremely low frequency (ELF) electromagnetic fields with alterations in calcium channel function and/or calcium ion flux and protein kinase C activity being implicated in the mediation of these effects. The present study was designed to examine the effects of nitric oxide (NO) and calcium ion/calmodulin-dependent nitric oxide synthase (NOS) on opioid-induced antinociception and their involvement in mediating the inhibitory effects of exposure to ELF magnetic fields. We observed that enkephalinase (SCH 34826)-induced, and likely enkephalin-mediated, antinociception in the land snail, Cepaea nemoralis, as measured by the enhanced latency of a foot withdrawal response to a thermal (40 degreesC) stimulus, was reduced by the NO releasing agent, S-nitro-N-acetylpenicillamide (SNP), and enhanced by the NO synthase inhibitor, NG-nitro-l-arginine methyl ester (l-NAME). Exposure of snails to an ELF magnetic field (15 min, 60 Hz, 141 microT peak) also reduced the enkephalinase-induced antinociception. The inhibitory effects of the 60-Hz magnetic field were significantly reduced by the NO synthase inhibitor, l-NAME, and significantly enhanced by the NO releasing agent, SNP, at dosages which by themselves had no evident effects on nociceptive sensitivity. These results suggest that: (1) NO and NO synthase have antagonistic effects on opioid-induced analgesia in the snail, Cepaea and (2) the inhibitory effects of ELF magnetic fields on opioid analgesia involve alteration in NO and NO synthase activity.

Animals↗

PubMed1998

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.

Animals↗

PubMed1998

Plasma testosterone levels are related to various aspects of locomotor activity in wild-caught male meadow voles (Microtus pennsylvanicus).

The relationship between plasma testosterone levels and locomotor activity in wild-caught sexually mature male meadow voles (Microtus pennsylvanicus) was assessed in the laboratory. Several aspects of locomotor activity were monitored for 1 h on two consecutive days using the automated Digiscan activity monitoring system. Plasma testosterone levels were determined immediately following the second day of activity monitoring. Significant Pearson correlations were obtained between plasma testosterone levels and total distance traveled [r(10) = 0.55, p < 0.05] and amount of time spent in movement [r(10) - 0.55, p < 0.05] on the second day. The wild voles showed a reduction in activity levels from the first to the second day of activity monitoring, which is indicative of habituation to a novel environment. This study provides direct evidence for a significant correlation between laboratory measures of behavioral activity and plasma testosterone levels in a wild-caught rodent. These findings indicate that previous assessments of hormone-behavior relationships in laboratory-bred rodents are consistent with the relationship between hormones and behavior in wild rodents.

Activity Cycles↗

PubMed1998

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.

Animals↗

PubMed1998

Analgesic effects of a specific pulsed magnetic field in the land snail, Cepaea nemoralis: consequences of repeated exposures, relations to tolerance and cross-tolerance with DPDPE.

It has been demonstrated previously that a short acute exposure to a specific extremely low frequency pulsed magnetic field (Cnp) can induce significant partly opioid-mediated analgesia in the land snail, Cepaea nemoralis. Here, this Cnp-induced analgesia is examined for the development of tolerance to daily repeated acute exposures of 15 or 30 min duration. Acute cross-tolerance to the delta opioid receptor directed agonist DPDPE, [D-Pen2, D-Pen5]enkephalin, was also found. Before (pre-exposure) and after (0, 15, 30 and 60 min) exposure to either a sham or Cnp magnetic field, snails were tested for an aversive reaction to a warmed surface (40 degrees C), and the latency time to the aversive reaction was recorded. Snails that were exposed to the Cnp showed a significant increase in the latency time (F1.55 = 2856.4; p < 0.001; Eta2 = 0.95), which may be interpreted as an induction of analgesia. During the daily (9 day) repeated acute exposures, the induction of analgesic response was significantly reduced, but not ablated. Altering the environmental conditions of the Cnp exposure restored a significant proportion of the partly developed tolerance, consistent with previous reports of environmental specificity in the development of opioid tolerance. These findings suggest that the partial development of tolerance to the opioid-mediated portion of Cnp-induced analgesia may be countered by altering the specific environmental Cnp exposure conditions.

Analgesia↗