Abnormal feeding behavior of western toads ( Bufo boreas) kept in a hyperosmotic environment. I. A quantitative behavioral analysis as related to cerebral amino acid concentrations

Abstract

Discriminant analysis of eleven behavioral variables associated with feeding permitted the assignment of hyperosmotically-acclimating (HOA) toads ( Bufo boreas) to six different behavioral states. These behavioral states could be correlated with specific alterations in the level of select amino acids in three regions of the toad's central nervous system. By considering only those amino acids that showed equivalent levels in corresponding brain regions of normally-behaving, freshwater-acclimating (FWA) and HOA toads, it was possible to focus upon just nine amino acids as possible modulators of feeding behavior. Four of these amino acids were markedly elevated in two or more abnormal behavioral states: gamma-aminobutyric acid (GABA) in all three brain areas; glutamate in the cerebral hemispheres; aspartate in the cerebral hemispheres and olfactory bulbs; and phenylalanine in the olfactory bulbs and optic lobes. Other possible behavior modulators identified were: lysine and threonine in the cerebral hemispheres; carnosine in the olfactory bulbs; and valine and alanine in the optic lobes.