Cortisol is an important indicator of health and behavioral state in fishes, and is produced in response to stressors including confinement, handling and social conflict. An inherent difficulty in measuring circulating cortisol is the implementation of invasive procedures that can be potent stressors. Recent studies show that cortisol can be reliably quantified from fish holding water by placing individuals in a small beaker for a predetermined collection period. We investigated whether convict cichlid fish (Amatitlania nigrofasciata) mount a significant stress response to beaker confinement and whether they habituate to the collection method. We also determined the relationship between plasma and water-borne cortisol, and changes in cortisol release rates following handling and cortisol administration. Initial beaker exposure induced high cortisol release rates but cichlids quickly habituated after 3-4 exposures. We revealed significant positive correlations between plasma and water-borne cortisol, and marked increases in water-borne cortisol release rates after cortisol injection that persisted for between 4 and 24 h, depending on the dosage. In conclusion, we provide convincing evidence for the utility and validity of the water-borne collection method to measure cortisol release rates in convict cichlids.
Domestication causes behavior and brain size changes in many species. We addressed three questions using clonal rainbow trout lines: What are the mirror-elicited aggressive tendencies in lines with varying degrees of domestication? How does brain size relate to genotype and domestication level? Finally, is there a relationship between aggressive behavior and brain size? Clonal lines, although sampling a limited subset of the species variation, provide us with a reproducible experimental system with which we can develop hypotheses for further research. We performed principal component analyses on 12 continuous behavior and brain/body size variables and one discrete behavioral variable ("yawn") and detected several aggression syndromes. Two behaviors, "freeze" and "escape", associated with high domestication; "display" and "yawn" behavior associated with wild lines and "swim against the mirror" behavior associated with semi-wild and domestic lines. Two brain size traits, total brain and olfactory volume, were significantly related to domestication level when taking total body size into account, with domesticated lines having larger total brain volume and olfactory regions. The aggression syndromes identified indicate that future QTL mapping studies on domestication-related traits would likely be fruitful.
Serotonin 2A receptors (5-HT 2A Rs) mediate the hallucinogenic effects of psychedelic drugs and are a key target of the leading class of medications used to treat psychotic disorders. These findings suggest that dysfunction of 5-HT 2A Rs may contribute to the symptoms of schizophrenia, a mental illness characterized by perceptual and cognitive disturbances. Indeed, numerous studies have found that 5-HT 2A Rs are reduced in the brains of individuals with schizophrenia. However, the mechanisms that regulate 5-HT 2A R expression remain poorly understood. Here we show that a physiologic environmental stimulus, sleep deprivation, significantly upregulates 5-HT 2A Rs levels in the mouse frontal cortex in as little as 6–8 hours (for mRNA and protein, respectively). This induction requires the activity-dependent immediate early gene transcription factor early growth response 3 ( Egr3 ) as it does not occur in Egr3 deficient (−/−) mice. Using chromatin immunoprecipitation, we show that EGR3 protein binds to the promoter of Htr2a , the gene that encodes the 5-HT 2A Rs, in the frontal cortex in vivo , and drives expression of in vitro reporter constructs via two EGR3 binding sites in the Htr2a promoter. These results suggest that EGR3 directly regulates Htr2a expression, and 5-HT 2A Rs levels, in the frontal cortex in response to physiologic stimuli. Analysis of publicly available post-mortem gene expression data revealed that both EGR3 and HTR2A mRNA are reduced in the prefrontal cortex of schizophrenia patients compared to controls. Together these findings suggest a mechanism by which environmental stimuli alter levels of a brain receptor that may mediate the symptoms, and treatment, of mental illness.
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