The central nucleus of the inferior colliculus in the cat

Abstract

The central nucleus of the inferior colliculus in the cat is distinguished by its unique neuropil. In Golgi-impregnated material, it is composed primarily of neurons with disc-shaped dendritic fields arranged into parallel arrays, or laminae, complemented by the laminar afferent axons from the lateral lemniscus. Large, medium-large, medium, and small varieties of disc-shaped cells are distinguished on the basis of the size of the dendritic field and cell body size, dendritic diameter, and dendritic appendages. A second major class of neurons in the central nucleus are the stellate cells with dichotomously branched, spherical-shaped dendritic trees. Simple, complex, and small stellate cells can be distinguished by their size and by the complexity of the dendritic and axonal branching. Laminar afferent axons are recognized by the nests of collateral side branches and the grapelike clusters of terminal boutons--thick, thin, and intermediate-sized varieties are apparent. Other axon types include local collaterals of central nucleus neurons, some of which are distinguished by their frequent and complex collaterals. In the central nucleus, the configuration of the fibrodendritic laminae, the presence of subdivisions, and the banding of afferent axons suggest levels of organization which are superimposed on the synaptic arrangements of the individual cell and axon types. The laminar pattern, as studied in serial Golgi-impregnated sections, differs from previous reports. The central nucleus contains subdivisions which can be distinguished by their laminar pattern, different proportions of cell types, and the packing density of the cell bodies and axonal plexus. The patterns of degeneration observed in Nauta-stained material after lesions of caudal auditory pathways show that thick and fine afferent fibers form dense bands of degeneration separated by sparse, fine-fiber degeneration. The bands are thicker than individual laminae but smaller than the subdivisions. The intrinsic organization of the neurons and axons, combined with the laminar organization, subdivisions, and banding patterns, each may contribute different aspects to the processing of auditory information in the central nucleus.

Identification of cell types in brain slices of the inferior colliculus

“…This observation is consistent with previous classi®cation of stellate cells in the central nucleus based on simple or complex branching patterns. 33 It is also consistent with the present ®ndings that neurons with these discharge patterns have a different input resistance. Different cell types in the IC de®ned by discharge pattern may have different passive dendritic electrotonic properties since those properties directly re¯ect input resistance and dendritic morphology (see for example Refs 43 and 44).…”

“…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.…”