Anatomy and Physiology of Principal Cells of the Medial Nucleus of the Trapezoid Body (MNTB) of the Cat
Philip H. Smith1,
Philip X. Joris2, 3, and
Tom C. T. Yin2
1 Department of Anatomy and 2 Department of Neurophysiology, University of Wisconsin Medical School, Madison, Wisconsin 53706; and 3 Division of Neurophysiology, Medical School, KULeuven, B3000 Leuven, Belgium
The Journal of Neurophysiology Vol. 79 No. 6 June 1998, pp. 3127-3142.
Smith, Philip H., Philip X. Joris, and Tom C. T. Yin. Anatomy and physiology of principal cells of the medial nucleusof the trapezoid body (MNTB) of the cat. J. Neurophysiol. 79:3127-3142, 1998. We have recorded from principal cells of themedial nucleus of the trapezoid body (MNTB) in the cat's superiorolivary complex using either glass micropipettes filled with Neurobiotinor horseradish peroxidase for intracellular recording and subsequentlabeling or extracellular metal microelectrodes relying on prepotentialsand electrode location. Labeled principal cells had cell bodiesthat usually gave rise to one or two primary dendrites, whichbranched profusely in the vicinity of the cell. At the electronmicroscopic (EM) level, there was a dense synaptic terminal distributionon the cell body and proximal dendrites. Up to half the measuredcell surface could be covered with excitatory terminals, whereasinhibitory terminals consistently covered about one-fifth. Thedistal dendrites were very sparsely innervated. The thick myelinatedaxon originated from the cell body and innervated nuclei exclusivelyin the ipsilateral auditory brain stem. These include the lateralsuperior olive (LSO), ventral nucleus of the lateral lemniscus,medial superior olive, dorsomedial and ventromedial periolivarynuclei, and the MNTB itself. At the EM level the myelinated collateralsgave rise to terminals that contained nonround vesicles and, inthe LSO, were seen terminating on cell bodies and primary dendrites.Responses of MNTB cells were similar to their primary excitatoryinput, the globular bushy cell (GBC), in a number of ways. Thespontaneous spike rate of MNTB cells with low characteristic frequencies(CFs) was low, whereas it tended to be higher for higher CF units.In response to short tones, a low frequency MNTB cell showed enhancedphase-locking abilities, relative to auditory nerve fibers. Forcells with CFs >1 kHz, the short tone response often resembledthe primary-like with notch response seen in many globular bushycells, with a well-timed onset component. Exceptions to and variationsof this standard response were also noted. When compared withGBCs with comparable CFs, the latency of the MNTB cell responsewas delayed slightly, as would be expected given the synapse interposedbetween the two cell types. Our data thus confirm that, in thecat, the MNTB receives and converts synaptic inputs from globularbushy cells into a reasonably accurate reproduction of the bushycell spike response. This MNTB cell output then becomes an importantinhibitory input to a number of ipsilateral auditory brain stemnuclei.