A microdialysis study of the noradrenergic response in XXXX frontal cortex and hypothalamus to a conditioned cue for aversive, naturalistic environmental stimuli.

@entity35 @entity1063 @entity1508
RATIONALE: Extracellular @entity1063 concentration in the @entity35 forebrain is increased by aversive environmental stimuli. This study investigated whether conditioned cues for such stimuli have the same effect. METHODS: After training @entity35 to associate a tone (conditioned cue) with transfer from a neutral zone to a brightly lit zone of a light/dark shuttle-box (unconditioned stimulus), microdialysis probes were implanted into the frontal cortex and hypothalamus under @entity1508 anaesthesia. Changes in extracellular @entity1063 concentration were then monitored on exposure to the tone alone. Parallel experiments monitored @entity35 ' behaviour in the light arena. RESULTS: A single exposure to the light arena increased extracellular @entity1063 in the frontal cortex and the hypothalamus but neither a single, nor repeated, exposure to the tone alone had any effect. After conditioning trials, the tone alone increased extracellular @entity1063 in the frontal cortex but not the hypothalamus, whilst the tone+transfer to the light arena resulted in a prolonged increase in extracellular @entity1063 in both brain regions. The time that @entity35 spent within the light arena was also prolonged. CONCLUSIONS: Noradrenergic neurones in the frontal cortex, but not the hypothalamus, respond to conditioned cues for aversive environmental stimuli. However, prolongation of the noradrenergic response in both brain regions could contribute to the behavioural adaptation to such unconditioned stimuli.
