INCREMENTAL CHANGES IN EXTRACELLULAR NORADRENALINE AVAILABILITY IN THE FRONTAL-CORTEX INDUCED BY NATURALISTIC ENVIRONMENTAL STIMULI - A MICRODIALYSIS STUDY IN THE FREELY MOVING RAT

Changes in levels of extracellular noradrenaline (NA), 3,4-dihydroxyph enylacetic acid (DOPAC), and 5-hydroxyindole-3-acetic acid (5-HIAA) in the frontal cortex, induced by exposure of unrestrained, conscious ra ts to novel environments, were compared using in vivo microdialysis. N A efflux increased when rats were transferred to a novel cage, but thi s was not significant when compared with either basal efflux or with c hanges after equivalent handling in their home cage. Increasing the in tensity of illumination of the novel cage by fivefold significantly in creased NA efflux with respect to basal efflux but not handled control s. However, a sustained and significant increase in NA efflux (cf. bas al efflux or handled controls) was found when an unfamiliar conspecifi c was also present in the novel cage. In all cases, basal efflux was r estored within 1 h of returning rats to their home cage. Neither handl ing nor environmental stimuli described above affected DOPAC efflux. 5 -HIAA efflux was increased (of. basal) in the presence of an unfamilia r conspecific, but this increase was no greater than that in handled r ats. It is concluded that different naturalistic stimuli cause increme ntal changes in the levels of extracellular NA in the frontal cortex; these changes affect both phasic and tonic components of the response.