Sources of GABAergic input to the inferior colliculus of the rat

Abstract

We have studied the GABAergic projections to the inferior colliculus (IC) of the rat by combining the retrograde transport of horseradish peroxidase (HRP) and immunohistochemistry for gamma-amino butyric acid (GABA). Medium-sized (0.06-0.14 microliter) HRP injections were made in the ventral part of the central nucleus (CNIC), in the dorsal part of the CNIC, in the dorsal cortex (DCIC), and in the external cortex (ECIC) of the IC. Single HRP-labeled and double (HRP-GABA)-labeled neurons were systematically counted in all brainstem auditory nuclei. Our results revealed that the IC receives GABAergic afferent connections from ipsi- and contralateral brainstem auditory nuclei. Most of the contralateral GABAergic input originates in the IC and the dorsal nucleus of the lateral lemniscus (DNLL). The dorsal region of the IC (DCIC and dorsal part of the CNIC) receives connections mostly from its homonimous contralateral region, and the ventral region from the contralateral DNLL. The commissural GABAergic projections originate in a morphologically heterogeneous neuronal population that includes small to medium-sized round and fusiform neurons as well as large and giant neurons. Quantitatively, the ipsilateral ventral nucleus of the lateral lemniscus is the most important source of GABAergic input to the CNIC. In the superior olivary complex, a smaller number of neurons, which lie mainly in the periolivary nuclei, display double labeling. In the contralateral cochlear nuclei, only a few of the retrogradely labeled neurons were GABA immunoreactive. These findings give us more information about the role of GABA in the auditory system, indicating that inhibitory inputs from different ipsi- and contralateral, mono- and binaural auditory brainstem centers converge in the IC.

Reversible Inactivation of the Dorsal Nucleus of the Lateral Lemniscus Reveals Its Role in the Processing of Multiple Sound Sources in the Inferior Colliculus of Bats

“…The DNLL, like the ICc, is one of the principal targets of both the ipsilateral and contralateral LSOs (Glendenning et al, 1981;Ross et al, 1988;Shneiderman et al, 1988Shneiderman et al, , 1999Yang et al, 1996). The DNLL, in turn, sends strong GABAergic projections bilaterally to the ICc (Ross et al, 1988;Shneiderman et al, 1988Shneiderman et al, , 1999Gonzalez-Hernandez et al, 1996;Kelly et al, 1998). Thus, EI cells of the ICc are strongly innervated by both LSOs and DNLLs, the lower nuclei the neuronal populations of which are EI (Fig.…”

Encoding of temporal features of auditory stimuli in the medial nucleus of the trapezoid body and superior paraolivary nucleus of the rat

“…The main projection target of the SPON is the ipsilateral IC (Beyerl, 1978;Zook and Casseday, 1982;Adams, 1983;Nordeen et al, 1983;Willard and Ryugo, 1983;Saint Marie and Baker, 1990;Schofield, 1991;Gonzalez-Hernandez et al, 1996;Saldaña and Berrebi, 2000), and neuronal correlates of gap detection attributable to the inhibitory input from the SPON might be expected there. Gap detection has been studied extensively in the mouse, and behavioral gap detection thresholds (GDTs) have been compared to GDTs recorded in the mouse IC (Walton et al 1977).…”

Unilateral cochlear ablation before hearing onset disrupts the maintenance of dorsal nucleus of the lateral lemniscus projection patterns in the rat inferior colliculus

“…Together these observations suggest that a labeled band of DNLL input together with the adjacent unlabeled space is likely to form a layer composed of ipsilateral and contralateral projections. DNLL neurons utilize the neurotransmitter GABA and make symmetric synaptic contacts with the soma and proximal dendrites of IC neurons (Brunso-Bechtold et al, 1981;Adams and Mugnaini, 1984;Shneiderman et al, 1988Shneiderman et al, ,1993Bajo et al, 1993;Merchan et al, 1994;Gonzalez-Hernandez et al, 1996;Kelly and Li, 1997;Chen et al, 1999;van Adel et al, 1999). Although much more is known about the developmental mechanisms of glutamatergic circuit formation, important progress has been made in understanding the development of inhibitory circuits in the auditory brainstem such as those in the SOC (Kandler, 2004;Kandler and Gillespie, 2005).…”