Mossy fiber projections from the cuneate nucleus to the cochlear nucleus in the rat

Abstract

A reciprocal connection is known to exist between the cuneate nucleus, which is a first-order somatosensory nucleus, and the cochlear nucleus, which is a first-order auditory nucleus. We continued this line of study by investigating the fiber endings of this projection in the cochlear nucleus of rats using the neuronal tracer Phaseolus vulgaris leucoagglutinin in combination with ultrastructural and immunocytochemical analyses. In the cochlear nucleus, mossy fiber terminals had been described and named for their morphologic similarity to those in the cerebellum, but their origins had not been discovered. In the present study, we determined that the axonal projections from the cuneate region gave rise to mossy fiber terminals in the granule cell regions of the ipsilateral cochlear nucleus. The cuneate mossy fibers appear to be excitatory in nature, because they are filled with round synaptic vesicles, they make asymmetric synapses with postsynaptic targets, and they are labeled with an antibody to glutamate. The postsynaptic targets of the mossy fibers include dendrites of granule cells. This projection onto the granule cell interneuron circuit of the cochlear nucleus indicates that somatosensory cues are intimately involved with information processing at this early stage of the auditory system.

Granule Cell Activation of Complex-Spiking Neurons in Dorsal Cochlear Nucleus

“…These unknown cell types could then serve a role analogous to the climbing fibers in cerebellum. Unfortunately, current evidence argues against one possible candidate, the unipolar brush cell, which does not seem to receive somatosensory mossy fiber input (Wright and Ryugo, 1996).…”

“…Cartwheel cells are the subject of this paper; their axons terminate on both principal cell types as well as on other cartwheel cells (not shown) (Berrebi and Mugnaini, 1991;Golding and Oertel, 1995). Some of the mossy fiber (mf ) inputs to granule cells are from the representation of the pinna in the somatosensory dorsal column /spinal trigeminal nuclei (MSN ) (Young et al, 1995;Wright and Ryugo, 1996). Question marks indicate points of uncertainty in the circuitry.…”

Activation of muscarinic receptors increases the activity of the granule neurones of the rat dorsal cochlear nucleus—a calcium imaging study

“…Their axons travel towards the outer layers of the DCN, and eventually form the parallel fibre network which provides a major excitatory, glutamatergic input for the apical dendritic trees of the pyramidal cells, and for the superficially situated dendrites of the giant neurones ( [20,31,40]; for a review see [25]). Granule cells, in turn, are contacted by axons carrying somatosensory information, mainly originating from the cuneate nucleus.…”

“…Although the majority of the fibres contacting the granule cells are glutamatergic [1,31,40], some of them (e.g., the cochlear mossy fibres) are thought to release acetylcholine (ACh), as indirectly inferred by the acetylcholinesterase positivity detected in the granule cell region [20,31]. This observation raises the possibility that the activity of the granule cells may also be adjusted by cholinergic modulation.…”

Processing Afferent Proprioceptive Information at the Main Cuneate Nucleus of Anesthetized Cats

“…The rvCN projects to structures implicated in sensory and motor integration, including the inferior olive (Berkley et al, 1986;McCurdy et al, 1998), tectum (Hand and Van Winkle, 1977;Wiberg and Blomqvist, 1984;Berkley et al, 1986), red nucleus (Edwards, 1972;Berkley et al, 1986), and cochlear nuclei (Itoh et al, 1987;Weinberg and Rustioni, 1987;Wright and Ryugo, 1996). Accordingly, we hypothesized that the rvCN might also project to the mvCN to influence the activity of projection or cuneolemniscal (CL) cells sensitive to deep input from muscle proprioceptors.…”