Chapter IX Glutamate neurotransmission in the mammalian inner ear

Publisher Summary This chapter describes the central glutamate synapses and the principles underlying their structural and molecular organization by focusing on a set of putative glutamatergic synapses in the inner ear. The inner ear contains the cochlea, the vestibular endorgans, and the sensory organs for hearing and equilibrium. The receptor cells in these organs are termed “hair cells” because they are equipped with stereocilia that respond to mechanical stimulation. The first synapse in the sensory pathways is that between hair cells and primary afferent neurons. Glutamate is considered as the most likely neurotransmitter candidate in this synapse. This view is supported by a series of pharmacological and electrophysiological studies and by recent neurochemical and immunocytochemical investigations. Phosphate-activated glutaminase (PAG) is responsible for most of the glutaminase activity in the central nervous system (CNS). The hair cells are unable to maintain an intracellular gradient of PAG and the synaptic pole of these cells is not defined at any step prior to vesicular transmitter uptake.