The neuronal organization of the inferior colliculus of the adult cat. I. The central nucleus

Abstract

The intrinsic organization of the central nucleus of the inferior colliculus has been studied in the adult cat by means of the Golgi and Nauta techniques. On the basis of cytoarchitecture and fiber connections, the central nucleus can be divided into: (i) a smaller, dorsomedial division. consisting mainly of large cells and receiving fibers from the auditory cortex, lateral lemniscus and probably the central nucleus of the other side; (ii) a larger, ventrolatenzl division consisting mainly of medium and small cells but with some intermingled larger types. This part receives fibers from the lateral lemniscus only.The ventrolateral division has a pronounced laminar arrangement of cells, dendrites and axons. The laminae, although overlapping extensively, form an onion-like series of concentric, curved shells, most of which are incomplete except for those closest to the center of curvature in the dorsolateral part of the nucleus. It is probable that these laminae provide a basis for the pronounced tonotopic organization of neurons in the nucleus. The thickness of the laminae is determined by the dendritic ramifications of two principal cell types which are fusiform or bi-tufted. Other, multipolar and large cells have dendrites which lie across one or several laminae and may form a basis for interaction between laminae.Four axon types can be distinguished: T y p e I (lateral lemniscal) and type II (corticofugal) axons run parallel to the laminae but in opposite directions, though type I1 axons are confined to the parts of the laminae projecting into the large-celled, dorsomedial division. T y p e 111 axons are widely ramifying and may arise within the central nucleus or be another form of afferent fiber. Type I and I11 axons end in dense clusters of terminals on principal cells but as single e n passant terminals on multipolar cells. Type IV axons are the efferents of the inferior colIiculus and run a recurrent course through the central nucleus giving off collaterals which sometimes end on the parent cell.

Identification of cell types in brain slices of the inferior colliculus

“…In the cat, disc-shaped neurons have dendrites oriented in parallel to create ®bro-dendritic laminae, while stellate neurons are perpendicular to the laminae. 26,32,33,51,52 In the rat, the thickness of the dendritic tree, rather than the orientation is more diagnostic. Two neuron classes (¯at and less-¯at) are seen in adult rats, but both types parallel the laminae.…”

“…Morphology suggests the central nucleus of the IC should have two types of neurons based on the shape and orientation of the dendritic tree. 9,22,25,33,51 The principal neuron is discshaped (called the¯at neuron in rats) with dendrites that parallel the ®bro-dendritic laminae. A second, less common neuron with a different dendritic morphology is also found in all species studied (e.g.…”

Quantitative assessment of developing afferent patterns in the cat inferior colliculus revealed with calbindin immunohistochemistry and tract tracing methods

“…In the auditory midbrain, the inferior colliculus (IC) is comprised of a large, seemingly homogeneous, central nucleus (CNIC) surrounded by a complex and heterogeneous arrangement of several paracentral nuclei (Berman, 1968;Rockel and Jones, 1973a,b;Morest and Oliver, 1984 (Rockel and Jones, 1973a;Oliver and Morest, 1984). With only a few exceptions, all ascending hindbrain auditory pathways project to the CNIC and end in cochleotopic fashion within a series of these fibrodendritic layers.…”

“…The results reveal a neurochemical marker for one type of synaptic compartment in CNIC layers, banding, that is organized before hearing onset in kittens, but that may undergo some postnatal pruning. Keywords fibrodendritic laminae; banding pattern; calcium-binding proteins; lateral superior olivary nucleus; carbocyanine dyeIn the auditory midbrain, the inferior colliculus (IC) is comprised of a large, seemingly homogeneous, central nucleus (CNIC) surrounded by a complex and heterogeneous arrangement of several paracentral nuclei (Berman, 1968;Rockel and Jones, 1973a,b;Morest and Oliver, 1984 (Rockel and Jones, 1973a;Oliver and Morest, 1984). With only a few exceptions, all ascending hindbrain auditory pathways project to the CNIC and end in cochleotopic fashion within a series of these fibrodendritic layers.…”

“…aligned in parallel with overlapping sheets of afferent fibers (Rockel and Jones, 1973a;Oliver and Morest, 1984). With only a few exceptions, all ascending hindbrain auditory pathways project to the CNIC and end in cochleotopic fashion within a series of these fibrodendritic layers.…”