Intracellular Recordings in Response to Monaural and Binaural Stimulation of Neurons in the Inferior Colliculus of the Cat

Abstract

The inferior colliculus (IC) is a major auditory structure that integrates synaptic inputs from ascending, descending, and intrinsic sources. Intracellular recording in situ allows direct examination of synaptic inputs to the IC in response to acoustic stimulation. Using this technique and monaural or binaural stimulation, responses in the IC that reflect input from a lower center can be distinguished from responses that reflect synaptic integration within the IC. Our results indicate that many IC neurons receive synaptic inputs from multiple sources. Few, if any, IC neurons acted as simple relay cells. Responses often displayed complex interactions between excitatory and inhibitory sources, such that different synaptic mechanisms could underlie similar response patterns. Thus, it may be an oversimplification to classify the responses of IC neurons as simply excitatory or inhibitory, as is done in many studies. In addition, inhibition and intrinsic membrane properties appeared to play key roles in creating de novo temporal response patterns in the IC.

Identification of cell types in brain slices of the inferior colliculus

“…The stimuli used for prehyperpolarization in this study were comparable in amplitude but longer than inhibitory postsynaptic potentials observed in vivo. 18,37 Examples of speci®c K 1 currents in the IC are consistent with morphological studies that show many K 1 channel subunits are present in the IC but are restricted to subsets of neurons. 34,38 Temporal coding versus signal transformations in the inferior colliculus Our present results in the IC parallel ®ndings in the auditory brainstem.…”

“…14,15,24 It is highly likely that the buildup± pauser neurons in the IC also contain an A-current 54 while other types of sustained neurons do not. The A-current in the IC buildup±pauser neuron may contribute to a buildup or pauser response after it is deinactivated by inhibitory synaptic potentials that commonly lead excitatory potentials in the IC 18 or by the larger after-hyperpolarization seen in sustained neurons (present results). The stimuli used for prehyperpolarization in this study were comparable in amplitude but longer than inhibitory postsynaptic potentials observed in vivo.…”

“…For example, neurons with similar binaural properties often have heterogenous morphology, indicating a lack of correlation, whereas the presence of inhibitory side bands is well correlated with stellate morphology. 18 The discharge patterns in the IC may be a useful method to classify neurons. Onset, sustained, buildup, and pauser discharge patterns are well-documented in many species (e.g.…”

Neuronal Responses to Lemniscal Stimulation in Laminar Brain Slices of the Inferior Colliculus

“…An underlying depolarization is seen in response to almost every acoustic stimulus unless there is a net inhibitory IPSP (Torterolo et al 1995;Kuwada et al 1997;Pedemonte et al 1997). Likewise, spikes ride on a sustained inward current in voltage-clamp recordings in vivo (Covey et al 1996).…”

“…The activation of excitatory and inhibitory synapses on ICC neurons during sound stimulation has been demonstrated by a few intracellular and wholecell recordings from ICC neurons in vivo (Torterolo et al 1995;Covey et al 1996;Kuwada et al 1997;Pedemonte et al 1997); however, most studies on excitation and inhibition in ICC have relied on extracellular recording techniques (Faingold et al 1993;Park and Pollak 1993a, b;Le Beau et al 1996; Palombi and Caspary 1996; Casseday et al 2000; Sivaramakrishnan et al 2004). Experiments in brain slices offer a controlled environment for the activation of synaptic inputs to ICC neurons and have allowed the pharmacological isolation and identification of specific synaptic currents (Moore et al 1998;Ma et al 2002a, b;Wu et al 2002Wu et al , 2004.…”