Physiology and Morphology of Cells in the Ventral Nucleus of Trapezoid Body and Rostral Periolivary Regions of the Rat Superior Olivary Complex Studied in Slices

Intracellular recordings were obtained from cells in ventral and rostral zones of the rat superior olivary complex, using slice preparations. Cell morphology was studied by injecting the cells with biocytin. All cells exhibited regular discharge patterns to current injection through the recording microelectrode. In some cases, cells exhibited irregular discharge patterns at certain current strengths. It was postulated that such irregular discharge patterns might arise either from the behaviour of intrinsic membrane conductances or inhibitory inputs. Three distinct action potential shapes were identified and correlations with cell morphology suggest that these may correspond to three functional categories of neurones in these regions; efferents to the cochlea, efferents to cochlear nucleus and neurones involved in circuitry within the superior olivary complex. Many of the biocytin-filled cells exhibited axon collaterals forming local terminal arbors within the superior olivary complex. The major excitatory input from trapezoid fibres was shown to be glutamatergic and blockable by CNQX. Cells could also receive inhibitory input, although the precise origin and pharmacology of this input was not determined.