Abstract
Recent research has identified the lateral habenula (LHb) as a brain region playing an important role in the production of stressful and anxiogenic states. Additionally, norepinephrine (NE) has long been known to be involved in arousal, stress and anxiety, and NE projections to the LHb have been identified emanating from the locus coeruleus (LC). The current research was devised to test the hypothesis that NE release within the LHb contributes to the occurrence of anxiogenic behaviors. Male rats were implanted with bilateral guide cannula aimed at the LHb and subsequently treated with intracranial (IC) infusions of the selective α(2) adrenergic autoreceptor agonist, dexmedetomidine (DEX) (0, 0.5, 1.0 μg/side), prior to assessment of ambulatory and anxiogenic behavior in tests of spontaneous locomotion, open field behavior, and acoustic startle-response. Results demonstrated that DEX administration significantly reduced the overall locomotor behavior of subjects at both doses indicating that infusion of even small doses of this α(2) agonist into the LHb can have profound effects on the subjects' general levels of alertness and activity. DEX was also found to attenuate anxiety as evidenced by a reduction in the magnitude of a startle-response to an acoustic 110 dB stimulus. Taken together, these results identify a role for NE release within the LHb in both arousal and anxiety.