Anatomy of the inferior colliculus in rat

Abstract

This paper defines the pattern of subdivision of the inferior colliculus in rat. It is based on serial sections of brains of albino and hooded rats cut in the frontal, sagittal and horizontal planes using Golgi, Nissl and a combined cell-myelin method. In rat, like in other mammals, the inferior colliculus consists of a central nucleus, an external cortex, and a dorsal cortex. The central nucleus is flattened in the frontal plane and confined to the caudomedial part of the inferior colliculus. It is characterized by a lamellar organization of disc-shaped neurons interspersed with multipolar cells. The cells are small to medium-sized. Although there is a dorsoventral gradient in size and packing density of cells within the nucleus, the overall size is smaller and the packing density larger than in adjacent subdivisions. The two cortices each consists of three layers. The outer-most layer is common to the two cortices, forming a fibrocellular capsule continuous along most of the circumference of the inferior colliculus. The external cortex is located lateral, rostral, ventral and ventrocaudal to the central nucleus. Its second layer, deep to the superficial capsule, is characterized by clusters of many small and a few medium-sized neurons in a myelin-dense neuropil. Layer 3, which constitutes the major portion of the subdivision, consists of relatively scattered, small, medium and large cells, the most characteristic element being large multipolar neurons with coarse Nissl granules. The dorsal cortex is located dorsocaudal and dorsomedial to the central nucleus. Its second layer is composed of small neurons, while the third, deep layer in addition contains medium-sized neurons. The cell density is intermediate to that of the central nucleus and the deep part of the external cortex. We have tried to facilitate the parcellation by reference to easily recognizable, nearby structures and to standard stereotaxic coordinates.

Identification of cell types in brain slices of the inferior colliculus

“…In experiments using sharp electrodes, 46/58 neurons were located in the central nucleus of the IC as de®ned by Faye-Lund and Osen. 7 The remaining 12 were studied in the rostral IC that contains several subdivisions, the intercollicular tegmentum, commissural nuclei, brachium of the IC, and remnants of the central nucleus. It corresponds to the rostral portion of external cortex.…”

“…It corresponds to the rostral portion of external cortex. 7 The majority of neurons studied with patch electrodes (n 41) were also in the central nucleus with additional neurons in the external and dorsal cortex.…”

The TLC: A Novel Auditory Nucleus of the Mammalian Brain

“…Third, with respect to the caudal third of the TLC, located within the IC, previous authors have mentioned a "commissural nucleus" or "interstitial nucleus" between the midline and the medial border of the dorsal cortex of the IC. However, the commissural region identified by these authors includes, but is not limited to, the caudal third of the TLC, and its continuity with the rostral two-thirds of the TLC was not in general noted (Geniec and Morest, 1971;Willard and Ryugo, 1983;Morest and Oliver, 1984;Faye-Lund and Osen, 1985;Herrera et al, 1987Herrera et al, , 1988a. Finally, another reason that the TLC may have gone unnoticed is that many commonly used neurochemical markers do not highlight the nucleus.…”

Immunolocalization of vesicular glutamate transporters 1 and 2 in the rat inferior colliculus

“…Neurons in the IC were differentiated based on size (Faye-Lund and Osen, 1985; Malmierca et al, 1993Malmierca et al, , 1995Morest & Oliver, 1984; Oliver refs. Peruzzi et al, 2000).…”