Development of opioid analgesic tolerance in rat to extended-release buprenorphine formulated for laboratory subjects.

Buprenorphine in an extended-release formulation intended for use in laboratory subjects is frequently administered to rats to provide extended analgesia without repeated handling. While levels of buprenorphine may persist in serum once extended-release buprenorphine has been introduced, exposure to opioids can cause opioid tolerance or opioid-induced hypersensitivity. This work examined the analgesic duration and efficacy of a single administration of extended-release buprenorphine intended for use in laboratory subjects in models of inflammatory pain and post-operative pain and the development of opioid tolerance in rat. After subcutaneous administration of 1 mg/kg extended-release buprenorphine, analgesic efficacy did not persist for the expected 72 hours. No changes were observed in mechanical thresholds in the hindpaws that were contralateral to the injury, suggesting a lack of centrally mediated opioid-induced hypersensitivity. To determine whether opioid tolerance arose acutely after one exposure to extended-release buprenorphine, we conducted the warm water tail flick assay; on Day 1 we administered either saline or extended-release buprenorphine (1 mg/kg) and on Day 3 we quantified the standard buprenorphine dose-response curve (0.1-3 mg/kg). Rats previously given extended-release buprenorphine displayed decreased analgesic responses after administration of standard buprenorphine as compared to the robust efficacy of standard buprenorphine in control subjects. Males appeared to show evidence of acute opioid tolerance, while females previously exposed to opioid did not demonstrate a decreased response at the doses examined. Taken together, these results suggest that opioid tolerance arises quickly in male rats after exposure to the extended-release formulation of buprenorphine. This tolerance may account for the brief period of antinociception observed.

Changes in women's feelings about their romantic relationships across the ovulatory cycle.

According to the dual mating hypothesis, women possess two overlapping suites of mate-choice mechanisms: one leading to preferences for sexually desirable men who have high-fitness genes and one leading to preferences for men who are able to invest in a woman and her children. Evidence increasingly demonstrates that women's preference for sexual desirability (but not investment attractiveness) increases when women are most fertile within the ovulatory cycle. Little is known, however, about the implications of these preference shifts for women's relationships with their long-term partners. Using luteinizing hormone tests to verify ovulation, across two studies (Samples 1 and 2), we found that women whose partners were relatively low in sexual desirability felt less close to their partner (Samples 1 and 2) and were more critical of their partner's faults (Sample 2) on high-fertility days of the cycle just prior to ovulation compared with low-fertility days of the cycle. Women whose partners were relatively high in sexual desirability felt closer to their partner (Sample 1) and more satisfied with their relationship (Sample 2) on high- than low-fertility days of the cycle. There were no such shifts in women's commitment to their relationship. Therefore, partner sexual desirability predicts women's high-fertility assessments of relationship quality but not their intentions to stay in their relationship, consistent with the dual mating hypothesis. These findings suggest that variations across the ovulation cycle in women's reproductive hormones play an important role in relationship dynamics.

Body odor attractiveness as a cue of impending ovulation in women: evidence from a study using hormone-confirmed ovulation.

Scent communication plays a central role in the mating behavior of many nonhuman mammals but has often been overlooked in the study of human mating. However, a growing body of evidence suggests that men may perceive women's high-fertility body scents (collected near ovulation) as more attractive than their low-fertility body scents. The present study provides a methodologically rigorous replication of this finding, while also examining several novel questions. Women collected samples of their natural body scent twice--once on a low-fertility day and once on a high-fertility day of the ovulatory cycle. Tests of luteinizing hormone confirmed that women experienced ovulation within two days of their high-fertility session. Men smelled each woman's high- and low-fertility scent samples and completed discrimination and preference tasks. At above-chance levels, men accurately discriminated between women's high- and low-fertility scent samples (61%) and chose women's high-fertility scent samples as more attractive than their low-fertility scent samples (56%). Men also rated each scent sample on sexiness, pleasantness, and intensity, and estimated the physical attractiveness of the woman who had provided the sample. Multilevel modeling revealed that, when high- and low-fertility scent samples were easier to discriminate from each other, high-fertility scent samples received even more favorable ratings compared with low-fertility scent samples. This study builds on a growing body of evidence indicating that men are attracted to cues of impending ovulation in women and raises the intriguing question of whether women's cycling hormones influence men's attraction and sexual approach behavior.

Sustained-release buprenorphine induces acute opioid tolerance in the mouse.

Sustained-release buprenorphine is widely used in mice with the intention of providing long-lasting analgesia. Statements about duration of therapeutic efficacy are based on persistence of serum buprenorphine levels over a minimum threshold, but behavioral data demonstrating sustained efficacy is not established. Additionally, chronic opioid exposure can induce tolerance and/or hyperalgesia; mice receiving sustained-release buprenorphine have not been evaluated for these effects. This study assessed clinical efficacy and duration of sustained-release buprenorphine in inflammatory, post-operative, and cancer pain; and screened for centrally-mediated opioid-induced hyperalgesia as well as opioid tolerance. At 1-2 mg/kg sustained-release buprenorphine, statistically significant analgesic efficacy occurred only at time points up to 2 h. These animals showed no changes in von Frey thresholds on the contralateral side, i.e. no centrally-mediated opioid hyperalgesia. To establish whether acute onset opioid tolerance resulted from a single sustained-release buprenorphine administration, we used the tail flick assay, exposing mice to sustained-release buprenorphine or saline on Day 1 and buprenorphine on Day 2. We measured duration and efficacy of 1 mg/kg buprenorphine after 1 mg/kg sustained-release buprenorphine, and also quantified a dose-response curve of buprenorphine (0.1-3 mg/kg) after 2 mg/kg sustained-release buprenorphine. Compared to control animals, mice previously exposed to sustained-release buprenorphine showed diminished analgesic response to buprenorphine; the resultant dose-response curve showed decreased efficacy. Pretreatment with naloxone, an opioid receptor antagonist, blocked sustained-release buprenorphine analgesic action. The short duration of antinociception following administration of sustained-release buprenorphine in mice is caused by the rapid development of tolerance.

Defining and Managing Pain in Stroke and Traumatic Brain Injury Research.

Neurologic conditions such as stroke and traumatic brain injury are challenging conditions to study in humans. Animal models are necessary to uncover disease processes and develop novel therapies. When attempting to model these or other neurologic diseases, the accompanying anesthesia and analgesia create variables that are not part of the onset of the clinical disease in the human population but are critical components of the postinjury care both in humans and animals. To maximize model validity, researchers must consider whether the disease process or a novel therapy is being studied. Damage to the neurons of the brain or the spinal cord is not painful at the neural tissue itself, but alterations to nociceptive signaling along the pain pathway can induce chronic pain. In addition, trauma or surgery leading to the event is associated with damage to peripheral tissue. Inflammation is inextricably associated with tissue injury. Inflammation is known to evoke nociception in the periphery and drive long-term changes to neurons in the CNS. Analgesics and anesthetics alter these responses yet are required as part of humane animal care. Careful planning for effective drug administration consistent with the standard of care for humans and equivalent animal care is required.

The Study of Pain in Rats and Mice.

Pain is a clinical syndrome arising from a variety of etiologies in a heterogeneous population, which makes successfully treating the individual patient difficult. Organizations and governments recognize the need for tailored and specific therapies, which drives pain research. This review summarizes the different types of pain assessments currently being used and the various rodent models that have been developed to recapitulate the human pain condition.

Seroprevalence of Brucella canis antibodies in dogs entering a Minnesota humane society, Minnesota, 2016-2017.

BACKGROUND: Canine brucellosis, caused by the bacterium Brucella canis, is a zoonotic and largely reproductive disease of dogs. The disease is a recognized problem in canine breeding populations, and the risk to individuals assisting with birthing is well described. Prior to 2015, all cases of canine brucellosis reported to the Minnesota Board of Animal Health were in dogs used for breeding. In 2015, canine brucellosis was identified in eight Minnesota rescue dogs, all originating from specific geographic areas in South Dakota. Our objective was to measure the seroprevalence of B. canis in stray and previously owned dogs entering a large Minnesota animal rescue organization to determine if our observations represented a localized or generalized disease issue among rescue dogs. METHODS: A stratified random sample of stray and previously owned dogs entering the largest Minnesota animal rescue organization between November 1, 2016 and November 7, 2017, was tested for B. canis antibodies by the 2-Mercaptoethanol Rapid Slide Agglutination Test (2ME-RSAT) (Zoetis d-TEC® CB kit). Sample sizes for each strata were calculated using previously published seroprevalence estimates. Blood from selected dogs was collected, serum harvested, and transported to the Minnesota Veterinary Diagnostic Laboratory for testing. Positive samples in the 2ME-RSAT were shipped to Cornell University for confirmation by Agarose Gel Immunodiffusion (AGID) testing. Demographics, state and setting of origin, and health status were collected on study-dogs. RESULTS: Of the 10,654 dogs accepted by AHS during the study period, 943 (8.9%) were selected for testing. Most study dogs arrived from Oklahoma (28%), Alabama (18%), and Minnesota (12%). The median age of study dogs was 1.5 years; 303 (32%) were intact males and 294 (31%) were intact females. Most study dogs were strays (n = 716, 76%). Of the total, 22 (3.1%) stray and eight (3.5%) owner-surrendered dogs were presumptively positive by RSAT; one (0.11%) of the stray dogs was positive by 2ME-RSAT and confirmed by AGID. The positive dog was a healthy-appearing 1 year-old neutered male beagle from Texas. CONCLUSIONS: The seroprevalence of canine brucellosis in dogs entering Minnesota for adoption from multiple states was low. Never-the-less, care must to be taken to consider all potential risks and outcomes of interstate and international dog trade, including the spread of infectious diseases such as canine brucellosis.

Ovulatory shifts in women's attractions to primary partners and other men: further evidence of the importance of primary partner sexual attractiveness.

Previous research has documented shifts in women's attractions to their romantic partner and to men other than their partner across the ovulation cycle, contingent on the degree to which her partner displays hypothesized indicators of high-fitness genes. The current study set out to replicate and extend this finding. Forty-one couples in which the woman was naturally cycling participated. Female partners reported their feelings of in-pair attraction and extra-pair attraction on two occasions, once on a low-fertility day of the cycle and once on a high-fertility day of the cycle just prior to ovulation. Ovulation was confirmed using luteinizing hormone tests. We collected two measures of male partner sexual attractiveness. First, the women in the study rated their partner's sexual attractiveness. Second, we photographed the partners and had the photos independently rated for attractiveness. Shifts in women's in-pair attractions across the cycle were significantly moderated by women's ratings of partner sexual attractiveness, such that the less sexually attractive women rated their partner, the less in-pair attraction they reported at high fertility compared with low fertility (partial r = .37, p(dir) = .01). Shifts in women's extra-pair attractions across the cycle were significantly moderated by third-party ratings of partner attractiveness, such that the less attractive the partner was, the more extra-pair attraction women reported at high relative to low fertility (partial r = -.33, p(dir) = .03). In line with previous findings, we found support for the hypothesis that the degree to which a woman's romantic partner displays indicators of high-fitness genes affects women's attractions to their own partner and other men at high fertility.