Behavioral and neuroendocrine consequences of social subjugation across adolescence and adulthood

BACKGROUND: Social subjugation is a very significant and natural stressor in the animal kingdom. Adult animals defeated and subjugated during establishment of dominance hierarchies or territorial encounters can be highly submissive in future agonistic interactions. While much is know about the biological and behavioral consequences of winning and losing fights in adulthood, little is known about adolescence; a developmental period noted for impulsivity and heightened agonistic behavior. The present studies were undertaken to determine if the behavioral and neuroendocrine consequences of social subjugation are comparable in adolescent versus adult Syrian golden hamsters (Mesocricetus auratus). Male siblings were studied from adolescence into adulthood following exposure to counterbalanced episodes of either a benign stressor, i.e., isolation in a novel cage, or the more severe stressor of social subjugation. RESULTS: As adults, hamsters with a history of social subjugation in adolescence show high levels of aggression toward intruders as compared to siblings subjugated in adulthood. Sibling controls subjugated in adulthood are highly submissive with little or no aggressive behavior. However, when subjugated in adulthood, hamsters with the earlier history of subjugation are no different than their sibling controls, i.e., adult subjugation promotes submissive behavior. Sexual motivation is high in adult hamsters with adolescent subjugation and testosterone levels remained stable over adulthood. In contrast, sibling controls subjugated in adulthood show lower levels of sexual motivation and reduced levels of testosterone. Release of cortisol during agonistic encounters is blunted in animals subjugated in adolescence but not adulthood. Measures of anxiety are reduced in hamsters with adolescent subjugation as compared to their sibling controls. CONCLUSION: These data demonstrate a pronounced difference in behavior and neuroendocrinology between adolescent and adult hamsters in their response to social subjugation and suggest adolescence is a resilient period in development

Vasopressin-dependent flank marking in golden hamsters is suppressed by drugs used in the treatment of obsessive-compulsive disorder

BACKGROUND: Alterations in arginine vasopressin regulation and secretion have been proposed as one possible biochemical abnormality in patients with obsessive-compulsive disorder. In golden hamsters, arginine vasopressin microinjections into the anterior hypothalamus trigger robust grooming and flank marking, a stereotyped scent marking behaviors. The intensity and repetition of the behaviors induced by arginine vasopressin is somewhat reminiscent of Obsessive Compulsive Disorder in humans. The present experiments were carried out to test whether pharmacological agents used to alleviate obsessive compulsive disorder could inhibit arginine vasopressin-induced flank marking and grooming. RESULTS: Male golden hamsters were treated daily for two weeks with either vehicle, fluoxetine, clomipramine, or desipramine (an ineffective drug), before being tested for arginine vasopressin-induced flank marking and grooming. Flank marking was significantly inhibited in animals treated with fluoxetine or clomipramine but unaffected by treatment with desipramine. Grooming behavior was not affected by any treatment. CONCLUSION: These data suggest that arginine vasopressin-induced flank marking may serve as an animal model for screening drugs used in the control of Obsessive Compulsive Disorder

Seed finding in golden hamsters: a potential animal model for screening anxiolytic drugs

Fasting hamsters overnight, followed by temporary isolation in a novel environment are stressful conditions that hamper their ability or motivation to find hidden sunflower seeds when returned to their home environment. Studies were done to test whether treatment with antianxiety drugs would reduce stress and shorten the latency to find the hidden seeds. Prior to testing, the animals were fasted for 18-20 h. Ninety minutes after intraperitoneal injection of test drugs (fluoxetine, buspirone, chlordiazepoxide, clozapine, desipramine, yohimbine), the animals were taken from their home cage and placed into a novel holding cage for 2 min. During their absence, 6 sunflower seeds were buried under the bedding in one corner of their home cage. The animals were placed back into their home cage and timed for their latency to find the seeds in a 5-min observation period. Treatment with anxiolytics caused a dose-dependent reduction in the latency to find the sunflower seed, while treatment with other psychotherapeutics were ineffective. Seed finding is an extremely sensitive bioassay, responding to anxiolytics given in doses as low as 1 microg/kg. These data provide evidence that seed finding in hamsters may serve as an animal model for screening potential anxiolytic drugs

Prenatal nicotine exposure and behavior

Prenatal exposure to nicotine has been associated with changes in behavioral indices in offspring. Flank marking, a scent-marking behavior in golden hamsters, appears to be controlled by arginine vasopressin (AVP) neurons in the hypothalamus. The present study examines the effects of prenatal exposure to nicotine on the vasopressinergic system associated with flank marking behavior

Pup suckling is more rewarding than cocaine: evidence from functional magnetic resonance imaging and three-dimensional computational analysis

NoNursing has reciprocal benefits for both mother and infant, helping to promote maternal behavior and bonding. To test the "rewarding" nature of nursing, functional magnetic resonance imaging was used to map brain activity in lactating dams exposed to their suckling pups versus cocaine. Suckling stimulation in lactating dams and cocaine exposure in virgin females activated the dopamine reward system. In contrast, lactating dams exposed to cocaine instead of pups showed a suppression of brain activity in the reward system. These data support the notion that pup stimulation is more reinforcing than cocaine, underscoring the importance of pup seeking over other rewarding stimuli during lactatio

Procedure for minimizing stress for fMRI studies in conscious rats

Functional magnetic resonance imaging (fMRI) in conscious animals is evolving as a critical tool for neuroscientists. The present study explored the effectiveness of an acclimation procedure in minimizing the stress experienced by the animal as assessed by alterations in physiological parameters including heart rate, respiratory rate, and serum corticosterone levels. Results confirm that as the stress of the protocol is minimized, there is a significant decrease in head movements and enhancement in data quality. The feasibility of improving the quality of fMRI data acquired in alert rats by utilizing a relatively simple technique is presented