Cell Types in the Mustached Bat Auditory Cortex

Abstract

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 IH/TV 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.

Fundamental differences between the thalamocortical recipient layers of the cat auditory and visual cortices

“…Spiny cells that are not stellate or pyramidal are occasionally encountered here but, as a group, do not display consistent anatomical or physiological features that might allow them to function as auditory cortical versions of the visual spiny stellates. Our data, combined with anatomical evidence from previous Golgi studies in several species, indicate that the spiny stellate is not the predominant or even a major cell type in any auditory thalamocortical recipient zone studied (McMullen and Glaser, 1982;Meyer and Ferres-Torres, 1984;Winer, 1984;Fitzpatrick and Henson, 1994).…”

“…Rose's observation may have foreshadowed observations of fundamental differences between layer 4 in auditory and other sensory cortices. Golgi studies in rabbit (McMullen and Glaser, 1982), cat (Winer, 1984), mustached bat (Fitzpatrick and Henson, 1994), and human (Meyer and Ferres-Torres, 1984;Meyer et al, 1989) showed that spiny stellates are rare in layer 4. In contrast to the symmetric dendritic trees of visual and somatosensory spiny stellates that are confined to layer 4, a great variety occurs in the dendritic arborization patterns of these infrequently encountered cells purported to be spiny stellate homologues.…”

“…If spiny stellate cells are not the primary excitatory cell type, what is? Several reports (McMullen and Glaser, 1982;Meyer et al, 1989;Fitzpatrick and Henson, 1994) indicate that pyramidal cells populate layer 4 in several species, although they are reported to be absent in cat primary auditory cortex (Winer, 1984).…”

On the presence of dendrite bundles in the cerebral cortex of the Madagascan lesser hedgehog tenrec and the red-eared pond turtle

“…This insectivore (suborder: Tenrecomorpha;Eisenberg 1981;Piccinini et al 1991;McPhee and Novacek 1993), was shown to have one of the lowest neocorticalization indices (Stephan et al 1991). In contrast to monotremes, marsupials and most other placental mammals, Echinops telfairi does not exhibit any granularization indicative of the presence of a lamina IV throughout its entire neocortex (Rehkämper 1981;Garey et al 1985;Rowe 1990;Glezer et al 1993;Fitzpatrick and Henson 1994;Krause and Saunders 1994;Nieuwenhuys 1994;Harman et al 1995). In this species, furthermore, some non-neocortical regions, such as the entorhinal and prepiriform cortices and the hippocampus, are characterized by a trilaminar architecture, with one main cellular layer situated between two layers consisting predominantly of neuropil.…”

Neuronal morphology in the African elephant (Loxodonta africana) neocortex

“…In the literature, there appears to be little agreement on whether these bifurcating apical branches are characteristic of bitufted (Bartesaghi et al 2003), multiapical (Ferrer et al 1986a, b), or even extraverted pyramidal neurons (Fitzpatrick and Henson 1994). Although resembling layer II extraverted pyramidal neurons in several other species (hedgehog, bat, and opossum: Sanides and Sanides 1972;dolphin: Glezer and Morgane 1990;quokka: Tyler et al 1998; humpback whale: Hof and Van der Gucht 2007; giant elephant shrew, giant and lesser anteater: Sherwood et al 2009), elephant superficial pyramidal neurons did not meet the strict definition of extraversion, whereby apical dendritic extent exceeds that of basilar dendrites (Sanides and Sanides 1972).…”