Biomedical subjects

Martin Kavaliers

Publications and source records attributed to Martin Kavaliers.

23 records · Page 2Linked to original sources

PubMed2003

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.

Adaptation, Physiological↗

PubMed2002

Acute effects of corticosterone on LiCl-induced rapid gustatory conditioning in rats: a microstructural analysis of licking patterns.

Acute administration of corticosterone (Cort) has been shown to potentiate a variety of learning processes. Here, the effects of Cort on rapid gustatory conditioning were examined using a lick monitoring system. Over a 3-day period, animals were given intraperitoneal (ip) injections of either a low dose of lithium chloride (LiCl; 0.75 mEq, ip) toxin or saline control (NaCl; 0.9%, ip) and then received an injection of Cort (5 mg/kg, ip) or cyclodextrin vehicle. In order to investigate the effect of acute increases in systemic Cort on gustatory conditioning, patterns of licking behavior were recorded while animals were exposed to a novel sucrose (0.3 M) tastant. Increased post-injection serum Cort levels were verified by radioimmunoassay analysis of trunk blood samples. Analysis of the licking patterns revealed evidence of rapid gustatory conditioning. Significantly reduced sucrose intake volumes and fewer total licks during the test sessions on Conditioning days were found in all groups that had received LiCl injections. Evidence of a Cort-potentiated conditioning effect was also found. Animals that had received Cort in addition to LiCl exhibited significantly shorter meal durations than did animals that had been administered LiCl alone and Cort significantly influenced the effects of LiCl on cluster number. These findings indicate that Cort facilitates conditioning, possibly by modulation of LiCl-induced visceral afferent and/or central feedback mechanisms.

Animals↗

PubMed1998

Sex differences in opioid and N-methyl-D-aspartate mediated non-opioid biting fly exposure induced analgesia in deer mice.

There is evidence for sex differences in responses to noxious stimuli and in the expression and mediation of analgesia. In particular, results of investigations with swim stress and the more ethologically appropriate stress of predator odor exposure have suggested sex differences in N-methyl-D-aspartate (NMDA) receptor system involvement in the mediation of analgesia. Whether or not this sex difference generalizes to other environmental stressors is, however, not clear. Biting flies are a natural aversive stimuli commonly encountered by wild and domestic animals and humans. The present study examined the opioid and non-opioid mediated nociceptive (50 degrees C hot plate) responses of reproductive male and female deer mice, Peromyscus maniculatus, exposed to biting fly attack. A 30 min exposure to biting flies (stable flies, Stomoxys calcitrans (L.)) elicited a naloxone sensitive, opioid-mediated analgesia that was of a greater magnitude in males than in female deer mice. In contrast, a 5 min exposure to biting flies elicited a 'on-opioid' analgesia that was of similar magnitude in both sexes and insensitive to both naloxone and the specific kappa opiate antagonist, nor-binaltorphimine. In male mice this non-opioid analgesia was antagonised by the competitive NMDA antagonist, NPC 1262, while in reproductive females the biting fly-induced analgesia was insensitive to NPC 12626. These results show that there are sex differences in NMDA involvement in the mediation of the non-opioid analgesia arising from brief exposure to the stress of biting fly attack. These data from a common, natural environmental challenge support the presence of basic sex difference in NMDA involvement in the mediation of stress-induced analgesia.

Amino Acids↗

PubMed1995

Sex differences in the expression and antagonism of swim stress-induced analgesia in deer mice vary with the breeding season.

Swim stress-induced analgesia (SSIA) was examined in photoperiodically induced 'breeding' (reproductive) and 'non-breeding' (non-reproductive) adult male and female deer mice, Peromyscus maniculatus. Nociceptive responses (50 degrees C, hot-plate) of breeding and non-breeding deer mice were determined after either a 1- or 3-min swim in 20 degrees C water. The 1-min swim induced an immediate and relatively short-lasting naloxone (1.0 mg/kg) insensitive 'non-opioid' -mediated SSIA that was antagonized by the N-methyl-D-aspartate (NMDA) antagonist, MK-801 (0.10 mg/kg) in all of the groups of mice except the breeding (reproductive) females. Breeding females displayed a non-opioid analgesia that was insensitive to MK-801. The 3-min swim induced a relatively more prolonged mixed opioid and 'non-opioid' SSIA of which the initial portion was sensitive to antagonism by MK-801 in all groups of the mice except the breeding females, while the latter portion (15 min after swim) was induced by naloxone in all of the groups of mice. Overall, the breeding males displayed greater levels of SSIA than the breeding females, with no consistent sex differences in the non-breeding mice. Within sexes, the breeding males displayed greater levels of opioid and non-opioid SSIA than the non-breeding males, while the non-breeding females displayed greater levels of SSIA than the breeding females. These results show that both sex and reproductive status affect the expression and neurochemical mediation of non-opioid SSIA. These findings also suggest that reproductive females may have an unique or novel hormonally (estrogen) dependent mechanism associated with the expression of SSIA.

Analgesia↗

PubMed1988

Day-night rhythms of opioid and non-opioid stress-induced analgesia: differential inhibitory effects of exposure to magnetic fields.

Day-night rhythms occurred in the naloxone-reversible (1.0 mg/kg), warm (opioid) and naloxone-insensitive, cold (non-opioid) swim stress-induced analgesia displayed by CF-1 mice. Maximum antinociceptive responses were evident at night, with the cold stress having significantly greater day- and night-time analgesic effects than the warm stress. An exposure for 30 min to a 0.5 Hz rotating magnetic field (1.5-90 gauss) reduced both the warm and cold stress-induced analgesia, with the magnetic stimuli having significantly greater inhibitory effects at night and on the opioid-induced responses. These results indicate that exposure to oscillating magnetic fields can significantly, and differentially, alter both opioid and non-opioid stress-induced analgesia and their day-night rhythms.

Analgesia↗