SPONTANEOUS AND AMPHETAMINE-EVOKED RELEASE OF CEREBELLAR NORADRENALINE AFTER SENSORIMOTOR CORTEX CONTUSION - AN IN-VIVO MICRODIALYSIS STUDYIN THE AWAKE RAT

Microdialysis sampling combined with HPLC was used to assess spontaneo us and d-amphetamine (AMPH)-evoked release of noradrenaline (NA) in th e cerebellum 1 day after probe implantation and 1 day after contusion of the right sensorimotor cortex (SMCX) in rats. In normal controls th e mean +/- SEM basal NA release was 10.08 +/- 0.97 pg in the left cere bellar hemisphere and 8.21 +/- 1.17 pg in the right hemisphere 22-24 h after probe implantation. The average +/- SEM NA release in a 3-h per iod after administration of AMPH (2 mg/kg, i.p.) increased to 453 +/- 47.35 pg in the left and to 402 +/- 49.95 pg in the right cerebellar h emisphere. NA release (range of 413-951% increase over baseline) was m aximal 20-40 min postdrug, returned to basal levels within 5 h, and re mained unchanged for the 22-24-h postdrug measurement period. Animals with a focal SMCX contusion had a marked depression of both spontaneou s and AMPH-evoked NA release. Mean +/- SEM basal NA release was 4.84 /- 1.09 pg in the left and 4.95 +/- 0.43 pg in the right cerebellar he misphere from 22 to 24 h postinjury, with NA levels increasing to 259 +/- 75.44 and 219 +/- 23.45 pg in the respective hemispheres over a 3- h period after AMPH. The maximal AMPH-induced increase in NA release r anged from 522 to 1,088% of basal levels in contused rats, with NA rel ease returning to predrug levels within 5 h and remaining depressed fo r at least 48 h postinjury. These data indicate that although neocorti cal injury results in a bilateral reduction of extracellular levels of NA in cerebellum, AMPH-releasable NA stores are present in the cerebe llum. These effects may be related to locomotor impairments and AMPH-f acilitated behavioral recovery after cortical injury.