Spontaneous and Amphetamine‐Evoked Release of Cerebellar Noradrenaline After Sensorimotor Cortex Contusion: An In Vivo Microdialysis Study in the Awake Rat

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Abstract
Microdialysis sampling combined with HPLC was used to assess spontaneous and d-amphetamine (AMPH)-evoked release of noradrenaline (NA) in the cerebellum 1 day after probe implantation and 1 day after contusion of the right sensorimotor cortex (SMCX) in rats. In normal controls the mean β SEM basal NA release was 10.08 β 0.97 pg in the left cerebellar hemisphere and 8.21 β 1.17 pg in the right hemisphere 22–24 h after probe implantation. The average β SEM NA release in a 3-h period after administration of AMPH (2 mg/kg, i.p.) increased to 453 β 47.35 pg in the left and to 402 β 49.95 pg in the right cerebellar hemisphere. NA release (range of 413–951% increase over baseline) was maximal 20–40 min postdrug, returned to basal levels within 5 h, and remained unchanged for the 22–24-h postdrug measurement period. Animals with a focal SMCX contusion had a marked depression of both spontaneous and AMPH-evoked NA release. Mean β SEM basal NA release was 4.84 β 1.09 pg in the left and 4.95 β 0.43 pg in the right cerebellar hemisphere from 22 to 24 h postinjury, with NA levels increasing to 259 β 75.44 and 219 β 23.45 pg in the respective hemispheres over a 3-h period after AMPH. The maximal AMPH-induced increase in NA release ranged from 522 to 1,088% of basal levels in contused rats, with NA release returning to predrug levels within 5 h and remaining depressed for at least 48 h postinjury. These data indicate that although neocortical injury results in a bilateral reduction of extracellular levels of NA in cerebellum, AMPH-releasable NA stores are present in the cerebellum. These effects may be related to locomotor impairments and AMPH-facilitated behavioral” recovery after cortical injury.