Acoustic and Current-Pulse Responses of Identified Neurons in the Dorsal Cochlear Nucleus of Unanesthetized, Decerebrate Gerbils

Abstract

In an effort to establish relationships between cell physiology and morphology in the dorsal cochlear nucleus (DCN), intracellular single-unit recording and marking experiments were conducted on decerebrate gerbils using horseradish peroxidase (HRP)- or neurobiotin-filled micropipettes. Intracellular responses to acoustic (tone and broadband noise bursts) and electric current-pulse stimuli were recorded and associated with cell morphology. Units were classified according to the response map scheme (type I to type V). Results from 19 identified neurons, including 13 fusiform cells, 2 giant cells, and 4 cartwheel cells, reveal correlations between cell morphology of these neurons and their acoustic responses. Most fusiform cells (8/13) are associated with type III unit response properties. A subset of fusiform cells was type I/III units (2), type III-i units (2), and a type IV-T unit. The giant cells were associated with type IV-i unit response properties. Cartwheel cells all had weak acoustic responses that were difficult to classify. Some measures of membrane properties also were correlated with cell morphology but to a lesser degree. Giant cells and all but one fusiform cell fired only simple action potentials (APs), whereas all cartwheel cells discharged complex APs. Giant and fusiform cells all had monotonic rate versus current level curves, whereas cartwheel cells had nonmonotonic curves. This implies that inhibitory acoustic responses, resulting in nonmonotonic rate versus sound level curves, are due to local inhibitory interactions rather than strictly to membrane properties. A complex-spiking fusiform cell with type III unit properties suggests that cartwheel cells are not the only complex-spiking cells in DCN. The diverse response properties of the DCN's fusiform cells suggests that they are very sensitive to the specific complement of excitatory and inhibitory inputs they receive.

Dorsal cochlear nucleus response properties following acoustic trauma: Response maps and spontaneous activity

“…Type II responses are recorded from vertical cells (Young, 1980;Rhode, 1999), which are one source of inhibition to DCN principal cells (Voigt and Young, 1990). The remaining examples, types III, IV-T, and IV are probably recorded from DCN principal cells (Young, 1980;Rhode and Kettner, 1987;Davis et al, 1996;Ding et al, 1999). They vary in the amount of inhibition, from Type III responses ( Fig.…”

“…Assuming that the relative numbers of principal-cell and non-principal cell types are the same in regions with elevated thresholds, we conclude that about half of the neurons with tail or non-classifiable responses were recorded from principal cells. The remainder would therefore come from vertical cells, which give type II responses in non-exposed animals, or type I/III neurons, whose anatomical sources are diverse and unknown, but probably include some principal cells (Ding et al, 1999;Spirou et al, 1999;Anderson and Young, 2004).…”

Encoding the Timing of Inhibitory Inputs

“…In response to sound, pyramidal cells can fire in one of four different discharge patterns: buildup, pauser, regular, or a combination of pauser and regular (Ding et al 1999;Godfrey et al 1975;Pfeiffer 1966;Rhode et al 1983). These patterns are distinguished by different FSLs and FISIs.…”

Early multisensory integration of self and source motion in the auditory system

“…Thus, monaural spectral cues that are processed within the DCN can contribute to horizontal sound localization (8). Furthermore, it has been shown that lesions of the DCN in cats result in increased error of head orientation to sound source, both in the vertical and horizontal plane (18).The auditory responses of the PNs in the DCN have been well characterized in cats (9, 19) and rodents (20)(21)(22). PNs have complex frequency response areas, showing both excitation and inhibition, and may therefore be especially sensitive to the spectral modulations introduced into the sound by the directionselective filtering action of the head and pinna (23,24).…”

“…The auditory responses of the PNs in the DCN have been well characterized in cats (9, 19) and rodents (20)(21)(22). PNs have complex frequency response areas, showing both excitation and inhibition, and may therefore be especially sensitive to the spectral modulations introduced into the sound by the directionselective filtering action of the head and pinna (23,24).…”