Synaptic organization of the mammalian olfactory glomerulus: new findings including an intraspecific variation

Abstract

The olfactory glomeruli of several mammalian species have been analyzed in serial thin sections. The types and frequencies of glomerular synaptic connections were determined in fields at least 8 μm × 8 μm × 7 μm in size.In all animals examined, axons of olfactory receptors synapsed onto mitral and tufted cell dendrites which were both pre- and postsynaptic to dendrites of periglomerular cells. Receptor cell axons synapsed onto periglomerular cell dendrites of the Mus musculus molossinus, dwarf Netherlands rabbit, and Sprague-Dawley rat, but receptor cell axons did not synapse onto periglomerular cell dendrites of the Balb/c mouse. Synapses between two periglomerular cell dendritic segments were noted in the rabbit, rat, and Balb/c mouse.We conclude that the synaptic arrangements found in the olfactory glomeruli of the molossinus, rabbit and rat are characteristic of the mammalian olfactory glomerulus, and that the synaptic connections of the Balb/c mouse represent a modification of this basic pattern. The finding that the olfactory glomeruli of two strains of mice possess different synaptic connections implies that data derived from even closely related experimental animals should be compared with caution.