Synaptic excitation in the dorsal nucleus of the lateral lemniscus

Abstract

The dorsal nucleus of the lateral lemniscus (DNLL) is a distinct auditory neuronal group located ventral to the inferior colliculus (IC). It receives excitatory and inhibitory afferent inputs from various structures of the auditory lower brainstem and sends GABAergic inhibitory efferents mainly to the contralateral DNLL and the bilateral IC. The synaptic excitation in DNLL neurons consists of two components, an early fast depolarization and a later long lasting one. Glutamate is the probable excitatory neurotransmitter for DNLL neurons. alpha-Amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors mediate the early part of the excitation while N-Methyl-D-aspartate (NMDA) receptors mediate the long lasting component. The long lasting NMDA receptor-mediated component in the DNLL may contribute to a prolonged inhibition in the IC. The DNLL is thought to be a structure for processing binaural information. Most DNLL neurons in rat and bat are sensitive to interaural intensity differences (IIDs). They are excited by stimulation of the contralateral ear and inhibited by stimulation of the ipsilateral ear, showing an excitatory/inhibitory (EI) binaural response pattern. The EI pattern can be attributed to synaptic inputs that originate from various structures in the lower auditory brainstem and impinge on the DNLL neurons. In cat some DNLL neurons are sensitive to IIDs and some are sensitive to interaural time differences. In addition, DNLL neurons exhibit different temporal response patterns to contralateral tonal stimulation and respond to amplitude modulated tones, implying that DNLL may contribute to processing temporally complex acoustic information. DNLL neurons shape binaural responses in the contralateral inferior colliculus and auditory cortex through their inhibitory brainstem projections and contribute to the accuracy with which animals localize sounds in space.