CHANGES IN THE RELEASE OF AMINO-ACID NEUROTRANSMITTERS IN THE BRAINS OF CALVES AND SHEEP AFTER HEAD-ONLY ELECTRICAL STUNNING AND THROAT CUTTING

In calves aged two to five months, throat cutting resulted in an incre ase in the concentration of the amino acid neurotransmitters glutamate and aspartate in the brain. Electrical head-only stunning by itself a lso increased the concentrations of these two neurotransmitters. The l evels induced by stunning resulted in a seizure state characterised by epileptiform-like activity in the electroencephalograph. Combing head -only stunning with throat cutting within 10 seconds of the stun had a synergistic effect upon glutamate and aspartate, increasing their con centration by a greater amount and more quickly than either procedure on its own. An irreversible loss of brain function also occurred more quickly than after throat cutting alone. The administration of glutama te and aspartate receptor antagonists before the throat cutting length ened the time to the loss of brain function in a dose dependent manner . Similar changes were observed in sheep but they occurred much more q uickly than in cattle.