Cells in auditory cortex that project to the cochlear nucleus in guinea pigs.
Animals; Auditory Cortex/*cytology; Cochlear Nucleus/*cytology; Fluorescent Dyes; Guinea Pigs; Pyramidal Cells/*cytology
Fluorescent retrograde tracers were used to identify the cells in auditory cortex that project directly to the cochlear nucleus (CN). Following injection of a tracer into the CN, cells were labeled bilaterally in primary auditory cortex and the dorsocaudal auditory field as well as several surrounding fields. On both sides, the cells were limited to layer V. The size of labeled cell bodies varied considerably, suggesting that different cell types may project to the CN. Cells ranging from small to medium in size were present bilaterally, whereas the largest cells were labeled only ipsilaterally. In optimal cases, the extent of dendritic labeling was sufficient to identify the morphologic class. Many cells had an apical dendrite that could be traced to a terminal tuft in layer I. Such "tufted" pyramidal cells were identified both ipsilateral and contralateral to the injected CN. The results suggest that the direct pathway from auditory cortex to the cochlear nucleus is substantial and is likely to play a role in modulating the way the cochlear nucleus processes acoustic stimuli.
Schofield Brett R; Coomes Diana L; Schofield Ryan M
Journal of the Association for Research in Otolaryngology : JARO
2006
2006-06
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1007/s10162-005-0025-4" target="_blank" rel="noreferrer noopener">10.1007/s10162-005-0025-4</a>
Control of a depolarizing GABAergic input in an auditory coincidence detection circuit.
Animals; Auditory Pathways/physiology; Biophysics; Brain Mapping; Chick Embryo; Cochlear Nucleus/*cytology; Electric Stimulation/methods; Excitatory Amino Acid Agents/pharmacology; GABA Agents/pharmacology; gamma-Aminobutyric Acid/*metabolism/pharmacology; In Vitro Techniques; Inhibitory Postsynaptic Potentials/drug effects/physiology; Nerve Net/*physiology; Neural Inhibition/drug effects/*physiology; Neurons/*physiology; Patch-Clamp Techniques/methods; Synaptic Transmission/drug effects/*physiology; Time Factors
Neurons in the chicken nucleus laminaris (NL), the third-order auditory neurons that detect the interaural time differences that enable animals to localize sounds in the horizontal plane, receive glutamatergic excitation from the cochlear nucleus magnocellularis (NM) and GABAergic inhibition from the ipsilateral superior olivary nucleus. Here, we study metabotropic glutamate receptor (mGluR)- and GABAB receptor (GABABR)-mediated modulation of synaptic transmission in NL neurons. Gramicidin-perforated recordings from acute brain stem slice preparations showed that the reversal potential of the GABAergic responses in NL neurons was more depolarized than the spike threshold. Activation of the GABAergic input produced a mix of inhibitory and excitatory actions in NL neurons. The inhibitory action is known to be critical in improving the acuity of temporal processing of sounds. The excitatory action, however, would reduce the phase locking fidelity of NL neurons in response to their excitatory inputs from the NM. We show that activation of presynaptic mGluRs or GABABRs by either exogenous agonists or synaptically released neurotransmitters reduced the GABAergic responses, preventing the excitatory action of GABA while leaving the inhibitory action intact. Unlike most CNS synapses, the glutamatergic transmission in the NL was not modulated by either mGluRs or GABABRs, indicating that fixed (nonmodulatory) excitatory inputs to the NL may be optimal for coincidence detection. This study contributes to our understanding of how selective neuromodulation is achieved to suit a particular function of neuronal circuits in the brain.
Tang Zheng-Quan; Gao Hongxiang; Lu Yong
Journal of neurophysiology
2009
2009-09
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1152/jn.00419.2009" target="_blank" rel="noreferrer noopener">10.1152/jn.00419.2009</a>