Connections of the dorsal nucleus of the lateral lemniscus: An inhibitory parallel pathway in the ascending auditory system?

Oct 8, 1988The Journal of comparative neurology

Inhibitory connections of the upper brainstem hearing pathway's dorsal lateral lemniscus nucleus

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Abstract

The dorsal nucleus of the lateral lemniscus (DNLL) has distinct afferent connections from the anteroventral cochlear nucleus and lateral superior olive.

DNLL is divided into three parts: dorsal, ventral, and lateral, which can be differentiated by cell size, shape, and orientation.
Afferent connections to DNLL include bilateral inputs from the anteroventral cochlear nucleus and lateral superior olive, and unilateral inputs from the medial superior olive and contralateral DNLL.
Connections to DNLL exhibit a tonotopic organization, with afferent fibers forming horizontal bands that span mediolaterally and rostrocaudally.
DNLL projects to the inferior colliculus and the contralateral DNLL, with projections showing a correspondence to areas of similar tonotopic organization.
In the inferior colliculus, DNLL axons terminate in prominent bands on the contralateral side and more diffuse patterns on the ipsilateral side.
Neurons in DNLL may utilize GABA as a neurotransmitter, suggesting a potential inhibitory function in the pathway to the inferior colliculus.

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This study examines the dorsal nucleus of the lateral lemniscus (DNLL) and its afferent and efferent connections. In Nissl-stained material, DNLL has three parts: dorsal, ventral, and lateral. Although each part contains neurons with similar Nissl patterns, the subdivisions may be distinguished by the size, shape, and orientation of the cells. The lateral DNLL contains a mixture of DNLL neurons and cells from the sagulum. Afferent connections to DNLL were investigated with anterograde axonal transport techniques. Bilateral inputs to DNLL arise from the anteroventral cochlear nucleus and lateral superior olive, while unilateral inputs are provided by the ipsilateral medial superior olive and the contralateral DNLL. The inputs appear to have a tonotopic organization. Afferent fibers to DNLL form horizontal bands that are continuous both mediolaterally and rostrocaudally. All parts of DNLL do not share the same inputs, and a medial-to-lateral gradient in the labeling of some pathways is evident. To study the efferent connections of DNLL, both retrograde and anterograde axonal transport techniques were used. The DNLL projects to the inferior colliculus and the contralateral DNLL. The topography of these projections suggests that areas of similar tonotopic organization are connected. In the inferior colliculus, the projection is heaviest to the central nucleus and extends to the adjacent dorsal and caudal cortex, the rostral pole nucleus, and the ventrolateral nucleus. Axons from DNLL terminate along the fibrodendritic laminae of the central nucleus as bands that are prominent on the contralateral side, whereas those on the ipsilateral colliculus are more diffuse. The afferent and efferent connections of DNLL constitute a multisynaptic pathway, parallel to the other ascending pathways to the inferior colliculus. The other ascending pathways include the direct pathways from the cochlear nucleus to the inferior colliculus and the indirect pathways via the superior olivary complex. Ascending pathways are discussed as to their relationship to the subdivisions of the inferior colliculus, the laterality of their projections, and their banding patterns in the central nucleus. In contrast to the excitatory pathways to the inferior colliculus, the neurons in DNLL may use GABA as a neurotransmitter. Axons from the DNLL terminate in the inferior colliculus as bands that could have a unique inhibitory function. Thus, the multisynaptic, DNLL pathway may provide feed-forward inhibitory inputs to the inferior colliculus, bilaterally, and to the contralateral DNLL.

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Connections of the dorsal nucleus of the lateral lemniscus: An inhibitory parallel pathway in the ascending auditory system?

Abstract

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