Projections of physiologically defined subdivisions of the inferior colliculus in the mustacbed bat: Targets in the medial geniculate body and extrathalamic nuclei

Abstract

This study examined the output of the central nucleus of the inferior colliculus to the medial geniculate body and other parts of the nervous system in the mustached bat (Pteronotus parnellii). Small deposits of anterograde tracers (horseradish peroxidase, [3H]leucine, Phaseolus vulgaris leucoagglutinin, wheat germ agglutinin conjugated to horseradish peroxidase, or biocytin) were made at physiologically defined sites in the central nucleus representing major components of the bat's echolocation signal. The topography, frequency specificity, and axonal morphology of these outputs were studied. The medial geniculate body was a major target of inferior collicular neurons, with three distinct input patterns. The projection to the ventral division was tonotopically organized, but had a relatively sparse contribution from neurons representing frequency modulated components of the biosonar pulse. The second input was to the rostral medial geniculate body, in which projections from inferior collicular neurons representing constant frequency sonar components were separated from those representing frequency modulated components. A third input was to the suprageniculate nucleus, which received strong, topographically arranged projections. Inputs to the dorsal nucleus and medial division were also observed. Extrathalamic regions receiving input included the pontine gray, external nucleus of the inferior colliculus, pericollicular tegmentum, nucleus of the brachium of the inferior colliculus, and pretectum. These central nucleus projections differed in organization and the structure of axon terminals, suggesting different physiological influences on their target nuclei. These results demonstrate that the central nucleus has divergent projections to various sensory and premotor nuclei, besides its well-established projection to the medial geniculate body.

Spectral Integration in the Inferior Colliculus of the Mustached Bat

“…There is an orderly progression from the highest frequencies located more caudally (59 kHz) to lower frequencies represented more rostrally. Our penetrations, which were angled 5-25°dorsocaudal to ventrorostral, are expected to encounter decreasing best frequencies with increasing depth, as have other studies using similar electrode orientations (Wenstrup et al, 1994;Wenstrup and Grose, 1995). All single units in the present study were recorded at depths of 125-1975 m, consistent with IC recordings of 10 -50 kHz responses in these previous studies using similar electrode angles.…”

“…Their presence in the auditory midbrain may be understandable in the context of sonar behavior, in which flight adjustments in response to target movement must be made within the 1-2 sec duration of an interception sequence. Projections of the IC to premotor centers could provide highly processed information useful for rapid changes in vocalization or flight (Schweizer, 1981;Frisina et al, 1989;Schuller et al, 1991a;Wenstrup et al, 1994;Casseday and Covey, 1996).…”

Functional Topography of Converging Visual and Auditory Inputs to Neurons in the Rat Superior Colliculus

“…The presence of retrogradely labeled cells in the ICx and CNIC in our hemisected midbrain preparation raises the possibility that some of the labeled axons in the SC were fibers of passage originating from these auditory structures. However, the projection from other regions of the IC to the nBIC (Doubell et al 2000;Wenstrup et al 1994) could also account for those retrogradely labeled neurons. Moreover, projections from elsewhere in the IC to the dSC are less likely to be functional in the slices because most of the axons would have been sectioned during the preparation of the slices.…”

Experimentally Induced Retinal Projections to the Ferret Auditory Thalamus: Development of Clustered Eye-Specific Patterns in a Novel Target

“…12C), but not in MGd or MGm. Studies in the cat (Kudo and Niimi, 1980) and bat (Wenstrup et al, 1994) have demonstrated that after injections of anterograde tracers in IC, terminal labeling in MGv appears as dense clusters of terminals aligned dorsoventrally, often forming "bands" (Fig. 12 B).…”