Differential distribution of neurotransmitter amino acids from the limbic system of aggressive and non-aggressive bull strains.

The amino acid content of crude synaptosomal fractions from the limbic system and related CNS regions showed significant differences between the aggressive Spanish fighting-bull and the non-aggressive Friesan bull breeds. Neurotransmitter amino acids (glutamate, aspartate, GABA and glycine) were the most unequally distributed. A higher ratio of excitatory to inhibitory neurotransmitter amino acids was always found in all the CNS regions studied in the aggressive breed. The concentrations of five non-transmitter amino acids (threonine, alanine, serine, leucine and isoleucine) showed minor variations between both studied bull strains and cannot be ascribed to differences in central energy metabolism. The results are explained in terms of a possible relationship between the amino acid neurotransmitter levels and the innate aggressiveness of the Spanish fighting-bull.