Neil Greenberg

University of Tennessee Knoxville, Ecology, Faculty Member

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Neil Greenberg received his doctorate from Rutgers University where he studied at both the Department of Zoology and the Institute of Animal Behavior. From work on reptile ethology at Rutgers, Greenberg moved to Paul D. MacLean’s Laboratory of Brain Evolution and Behavior at the National Institute of Mental Health. While there he was also appointed a Research Associate at Harvard University’s Museum of Comparative Zoology. In 1978, Greenberg joined the faculty of the Department of Ecology and Evolutionary Biology at the University of Tennessee, Knoxville, where he served as professor and Chairman of the University Studies Program, a university-wide interdisciplinary faculty development program. He has held adjunct faculty appointments in the Graduate School of Medicine and the Department of Psychology. He is presently Professor Emeritus. Greenberg is presently active with the research team of the University's Interdisciplinary Colloquy on Phenomenology and leads his integrative seminar, "Art and Organism," every spring.

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Todd Oakley

University of California, Santa Barbara

Catherine Toft

University of California, Davis

Leah R. Johnson

University of Chicago

Jana Javornik

University of East London

Yale University

Swansea University

Columbia University

University of Florida

Brendan Godley

University of Exeter

M. Anne Visser

University of California, Davis

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Activation of Central Biogenic Amines Following Aggressive Interaction in Male Lizards, Anolis carolinensis</i&gt

Brain Behavior and Evolution, 1995

Many stimuli, including social aggression, activate endocrine stress mechanisms, presumably media... more Many stimuli, including social aggression, activate endocrine stress mechanisms, presumably mediated or modulated by central neurotransmitters. To determine the effects of aggression on central neurochemistry, reproductively active male Anolis carolinensis were paired and allowed to establish social dominance relationships. While combatants cohabited, the fight losers invariably became socially subordinate and displayed darker color, selection of lower perch sites, and lower body posture than the winners. After one hour, one day, one week, or one month of cohabitation animals were sacrificed. Each member of a pair was killed at approximately the same time, along with animals kept isolated as controls. Diencephalon, non-optic lobe midbrain and hindbrain were analyzed for indoleamines, catecholamines and metabolites by coulochem electrode array HPLC. Early activation (by one hour) of the serotonergic system in subordinate male lizards was indicated by decreased serotonin (5-HT), increased 5-hydroxy-indoleacetic acid (5-HIAA) levels and 5-HIAA/5-HT ratio. Substrate 5-hydroxy-tryptophan (5-HTP) also increased in losing males, suggesting enhanced production as well as turnover. Significant 5-HTP and 5-HIAA/5-HT increases for subordinate males, compared with levels in control and dominant males, were greatest at one hour and diminished thereafter. This pattern of indoleamine system activation is consistent with stress-induced stimulation of the serotonergic system and prolonged activation of the stress response in subordinate animals, as well as serotonergic inhibition of aggression. In contrast with serotonin, subordinate males did not have increased catecholamine system activation following one hour of interaction. The ratio of DOPAC/dopamine was lower following one hour of interaction in subordinate males. Adrenergic system activation, indicated by metanephrine/epinephrine ratio, increased with time in losing males, except that after one month of cohabitation, turnover returned to levels that equaled those of control animals. Noradrenergic metabolite MHPG, as well as MHPG/NE ratio, were significantly reduced in dominant males at one hour and one week. Changes in adrenergic system activation, not seen in or registered by noradrenergic systems, indicate a possible role for central epinephrine in social stress accommodation.

Temporal patterns of limbic monoamine and plasma corticosterone response during social stress

Neuroscience, 2003

Dominant and subordinate males respond differently to the stress of social interaction. After an ... more Dominant and subordinate males respond differently to the stress of social interaction. After an hour of social interaction, subordinate male Anolis carolinensis have elevated serotonergic activity in hippocampus, but dominant males do not. In other species, and using other stressors, the activation of hippocampal serotonergic activity is much more rapid than one hour. To elucidate early stress responsiveness, adult male A. carolinensis were divided into four groups: isolated controls, and pairs of males sampled after 10, 20 or 40 minutes of aggressive interaction. Development of dominant-subordinate relationships was determined by behavior and by the celerity of eyespot darkening. Serotonergic activity in the hippocampus, nucleus accumbens and amygdala was elevated rapidly and equally in both dominant and subordinate males, as were plasma corticosterone concentrations. Serotonergic activity remained elevated through 40 minutes in hippocampus and nucleus accumbens. Only subordinate males had elevated corticosterone levels at 40 minutes. Social status does not impede socially induced stress responses. Rather, rapid regulation of serotonergic stress responses appears to be a mediating factor in determining both behavioral output and social status. Temporal expressions of monoaminergic and endocrine stress responses are distinctive between males of dominant and subordinate social status. Such temporal patterns of transmitter and glucocorticoid activity may reflect neurocircuitry adaptations that result in behavior modified to fit social status.

Neil Greenberg

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