Synaptic transmission in the rat medial superior olivary nucleus
thesisposted on 15.12.2014, 10:34 by Amanda Jane. Smith
The medial superior olivary (MSO) nucleus forms part of the binaural auditory pathway in the brain stem where it is involved in sound source localisation. It detects interaural time differences (ITDs) of sounds arriving at the two ears by functioning as a coincidence detector of the bilateral excitatory inputs from spherical bushy cells of the anterior ventral cochlear nuclei (AVCN). The MSO also receives a unilateral inhibitory synaptic input from globular bushy cells of the contralateral AVCN, via the medial nucleus of the trapezoid body (MNTB). Investigations in this thesis focus on the inhibitory synaptic input.;Transverse brain stem slices were prepared from 6-13 day old Lister Hooded rats and whole cell patch clamp recordings were made from visually identified MSO neurones. Synaptic currents were evoked using a bipolar platinum stimulating electrode positioned over the ipsilateral MNTB.;The excitatory synaptic input from the contralateral AVCN was mediated by glutamate receptors. Inhibitory postsynaptic currents (IPSCs), generated by stimulation of the ipsilateral MNTB reversed around the chloride equilibrium potential and were blocked by 1microM strychnine, suggesting them to be glycine receptor mediated. The EPSCs had a mean 10-90% rise time of 0.71+/-0.12ms (n=9) and decayed over a double exponential time course with time constants of 8.54+/-0.44ms and 41.50+/-1.84ms (n=81) at 25Â°C. The decay time course of the IPSC had a Q10 of ~2 and was slightly voltage-dependent. The IPSCs were also modulated by 5HT, metabotropic glutamate and GABA B receptors, the latter of which, based on miniature current analysis was suggested to be via a presynaptic site.;This work confirms that there is a functional synapse between the MNTB and MSO which is mediated by the inhibitory transmitter, glycine and hence suggests that models of sound source localisation should incorporate this important observation.