| Acoustic behaviors including orientation and social communication depend on neural integration of information across the sound spectrum. Spectral integration is performed by combination-sensitive (C-S) neurons, which show time-sensitive interactions (facilitatory and inhibitory) between distinct spectral elements in complex sounds. In the mustached bat (Pteronotus parnellii), C-S neurons are abundant in the inferior colliculus (IC). Facilitatory C-S neurons are thought to be created in the IC, but the origin of inhibitory interactions is unclear. The formation of C-S facilitation appears to require a low frequency-sensitive input that projects to high frequency representations in the IC. The cochlear nucleus (CN) may be a source of both low and high frequency inputs to combinatorial IC neurons. In addition, descending inputs may also play a role in the formation or modulation of complex responses properties, such as C-S responses. However, the origins of descending inputs onto IC neurons are unclear.; In the first set of experiments, I described basic response features of CN neurons that may be related to frequency integration in the IC. Using micropipette electrodes, I recorded single unit responses in mustached bats to tones and noise stimuli. I found that CN contains the appropriate range of low frequencies and some of the temporal features required for the formation of combinatorial neurons in the IC.; In the second set of experiments, I examined whether combinatorial responses were present in the CN. Using tracer-filled micropipettes and stereotaxic procedures, I recorded single unit responses in mustached bats to tones, noise, or combination of tones or noise. I found no facilitated combinatorial interactions in the CN. However, I found that combinatorial inhibitory neurons were common throughout the CN.; In my last set of experiments, I examined origins of descending inputs onto collicular neurons. I placed deposits of retrograde tracers at physiologically defined sites in the IC of mustached and pallid bats (Antrozous pallidus ), then searched for retrogradely labeled somata in the forebrain. I found that the amygdala and auditory cortex project bilaterally throughout the IC. Across experiments, the average number of labeled cells in the amygdala was similar to the auditory cortex. |
