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Rationale: Understanding the neurobiological mechanisms mediating dominance and competitive aggression is essential to understanding the development and treatment of various psychiatric disorders. Previous research suggests that these mechanisms are both sexually differentiated and influenced substantially by social experience. In numerous species, GABAA receptors in the lateral septum have been shown to play a significant role in aggression in males. However, very little is known about the role of these GABAA receptors in female aggression, the role of social experience on GABAA receptor–mediated aggression, or the roles of different GABAA subtypes in regulating aggression. Objectives: Thus, in the following set of experiments, we determined the role of social experience in modulating GABAA receptor–induced aggression in both male and female Syrian hamsters, with a particular focus on the GABAA receptor subtype mediating these effects. Results: Activation of GABAA receptors in the dorsal lateral septum increased aggression in both males and females. Social housing, however, significantly decreased the ability of GABAA receptor activation to induce aggression in males but not females. No significant differences were observed in the effects of GABAA receptor activation in dominant versus subordinate group-housed hamsters. Finally, examination of potential GABAA receptor subtype specificity revealed that social housing decreased the ratio of δ extrasynaptic to γ2 synaptic subunit GABAA receptor mRNA expression in the anterior dorsal lateral septum, while activation of δ extrasynaptic, but not γ2 synaptic, GABAA receptors in the dorsal lateral septum increased aggression. Conclusions: These data suggest that social experience can have profound effects on the neuronal mechanisms mediating aggression, especially in males, and that δ extrasynaptic GABAA receptors may be an important therapeutic target in disorders characterized by high levels of aggression. [ABSTRACT FROM AUTHOR]

The suprachiasmatic nucleus ( SCN) contains a circadian clock that generates endogenous rhythmicity and entrains that rhythmicity with the day-night cycle. The neurochemical events that transduce photic input within the SCN and mediate entrainment by resetting the molecular clock have yet to be defined. Because GABA is contained in nearly all SCN neurons we tested the hypothesis that GABA serves as this signal in studies employing Syrian hamsters ( Mesocricetus auratus). Activation of GABAA receptors was found to be necessary and sufficient for light to induce phase delays of the clock. Remarkably, the sustained activation of GABAA receptors for more than three consecutive hours was necessary to phase-delay the clock. The duration of GABAA receptor activation required to induce phase delays would not have been predicted by either the prevalent theory of circadian entrainment or by expectations regarding the duration of ionotropic receptor activation necessary to produce functional responses. Taken together, these data identify a novel neurochemical mechanism essential for phase-delaying the 'master' circadian clock within the SCN as well as identifying an unprecedented action of an amino acid neurotransmitter involving the sustained activation of ionotropic receptors. [ABSTRACT FROM AUTHOR]

Rationale: Understanding the neurobiological mechanisms mediating dominance and competitive aggression is essential to understanding the development and treatment of various psychiatric disorders. Previous research suggests that these mechanisms are both sexually differentiated and influenced substantially by social experience. In numerous species, GABA A receptors in the lateral septum have been shown to play a significant role in aggression in males. However, very little is known about the role of these GABA A receptors in female aggression, the role of social experience on GABA A receptor-mediated aggression, or the roles of different GABA A subtypes in regulating aggression., Objectives: Thus, in the following set of experiments, we determined the role of social experience in modulating GABA A receptor-induced aggression in both male and female Syrian hamsters, with a particular focus on the GABA A receptor subtype mediating these effects., Results: Activation of GABA A receptors in the dorsal lateral septum increased aggression in both males and females. Social housing, however, significantly decreased the ability of GABA A receptor activation to induce aggression in males but not females. No significant differences were observed in the effects of GABA A receptor activation in dominant versus subordinate group-housed hamsters. Finally, examination of potential GABA A receptor subtype specificity revealed that social housing decreased the ratio of δ extrasynaptic to γ 2  synaptic subunit GABA A receptor mRNA expression in the anterior dorsal lateral septum, while activation of δ extrasynaptic, but not γ 2  synaptic, GABA A receptors in the dorsal lateral septum increased aggression., Conclusions: These data suggest that social experience can have profound effects on the neuronal mechanisms mediating aggression, especially in males, and that δ extrasynaptic GABA A receptors may be an important therapeutic target in disorders characterized by high levels of aggression.