Cell types in the mustached bat auditory cortex

Cells in the auditory cortex of the mustached bat were studied with Golgi stains. No cell types appeared to be unique to the mustached bat auditory cortex or to specialized functional areas, but the laminar proportions and distributions of cell types were somewhat different from that reported for primary sensory cortex of other species. Two major cell types were distinguished, those with dendritic spines and those without spines. Non-spiny neurons were concentrated deep in layer III/IV and in layer V, and had three types of dendritic patterns, multipolar, bitufted and bipolar. Many of the non-spiny neurons were large; some nearly equaled the largest pyramidal neurons in size. Five types of spiny neurons were identified, pyramidal cells, extraverted pyramidal cells, 'spiny stellate-like' neurons, and multiform cells. In the narrow, densely packed, 'accentuated' layer II, slightly more than half of the spiny neurons were extraverted pyramidal cells, which are characterized by multiple, widely diverging apical dendrites. The high concentration of layer II extraverted pyramidal neurons is consistent with descriptions of the 'accentuated' layer II previously reported in other bat species and 'basal' insectivores. The remaining spiny neurons in layer II, and the preponderance of spiny neurons in layers III-VI, were typical pyramidal neurons that had single apical dendrites and tufts of basal dendrites. The thalamic recipient zone (deep layer III/IV) contained few candidates for spiny stellate cells, so a major constituent of the thalamic recipient zone in primary sensory cortex of many species is only a minor cellular component in the mustached bat auditory cortex.