Laminar distribution of putative neurotransmitter amino acids and ligand binding sites in the dog olfactory bulb.

Coronal sections of frozen dog olfactory bulb have been dissected into four anatomically distinct layers. The laminar distribution of ten amino acids, the dipeptide carnosine, and nine [3H]ligand binding sites in these layers was determined. GABA and tyrosine levels were highest in the mitral cell-granule cell layer, and glutamate levels were slightly elevated in the glomerular layer. The distributions of all other amino acids did not show significant differences across the layers. Carnosine was predominantly localized in the fiber and glomerular layers. With the exception of quinuclidinyl benzilate, the [3H]ligand binding sites showed more discrete distributions. Muscimol, diazepam, kainic acid, and spiroperidol binding were predominantly localized in the mitral cell-granule cell layer, where clonidine binding was at a minimum. Dihydromorphine binding was high in both the fiber and the mitral cell-granule cell layers. Carnosine binding was maximal in the glomerular layer. The implications of these observations with regard to biochemical and neurophysiological data are discussed.