Projection from the inferior colliculus to the superior olivary complex in the albino rat

Abstract

The origin and termination of the fibers projecting from the inferior colliculus to the superior olivary complex have been studied in rat by means of the Fink and Heimer and horseradish peroxidase techniques (anterograde and retrograde transport of free horseradish peroxidase and peroxidase conjugated to wheat germ agglutinin). The colliculoolivary fibers originate in layer 3 of the external cortex and the adjacent part of the central nucleus, particularly in the former. Via the lateral lemniscus the fibers reach the ipsilateral periolivary region where they terminate in the rostral and medioventral zones. The terminal field contains at least two types of cells which could constitute the next link in the descending projection to the cochlea and/or the cochlear nuclei. One of these is the large olivocochlear neuron, and the other a smaller neuron projecting to the cochlear nuclei. Judged by their topographic relationship in the inferior colliculus and in the superior olive, the colliculoolivary neurons may form a link in a oligosynaptic projection from the auditory cortex to the cochlea and/or the cochlear nuclei. The observations are based on light microscopy, however, and do not allow conclusions concerning synaptic contacts.

Distribution and possible functional roles of some neuroactive peptides in the mammalian superior olivary complex

“…mRNA for CCK is found abundantly in neurones of the central nucleus of the inferior colliculus (Schiffmann and Vanderhaeghen, 1991;Wynne et al, 1995) and this higher centre is known to be a source of descending projections to the SOC (Caicedo and Herbert, 1993;Faye-Lund, 1986;Schofield and Cant, 1999;Thompson and Thompson, 1993;Vetter et al, 1993). As has already been mentioned, injection of anterograde tracer into the central nucleus of inferior colliculus gives rise to terminals within the ventral-most parts of the VNTB whose distribution within this nucleus is similar to that of CCKlabeled fibres.…”

Ultrastructure of synaptic input to medial olivocochlear neurons

“…Previous work has shown that OC neurons receive inputs from two subdivisions of the cochlear nucleus (Warr, 1969;Robertson and Winter, 1988;Thompson and Thompson, 1991a;Ye et al, 2000), from the inferior colliculus (Faye-Lund, 1986;Thompson Fig. 8.…”

“…One descending source of input is from the inferior colliculus (Faye-Lund, 1986;Thompson and Thompson, 1993;Vetter et al, 1993). The MOC neurons can be activated by stimulating the inferior colliculus and the activation produces cochlear effects (Mulders and Robertson, 2000c;Ota et al, 2004).…”

Distribution of descending projections from primary auditory neocortex to inferior colliculus mimics the topography of intracollicular projections

“…Recent anatomical Vetter et al, 1993) and physiological (Rajan, 1990) data indicate that descending collicular fibers contact medial olivocochlear neurons, suggesting a direct relationship between the second and the third steps of the descending auditory pathway. The situation, however, is less clear within the IC: Whereas most descending neocortical fibers seem to innervate the dorsal and lateral regions of the IC, but not its central nucleus (CNIC; reviewed by Faye-Lund, 1985;Herbert et al, 1991), most colliculoolivary neurons are located more ventrally, mainly in the CNIC and the external cortex of the IC (ECIC; Faye-Lund, 1986). According to these data, there would be a partial, but presumably significant, segregation between the place of termination of the corticocollicular fibers and the location of the colliculoolivary neurons; those colliculoolivary neurons located in the CNIC do not appear to be under direct neocortical influence.…”