Synaptic Transmission and Neural Circuits

Northeastern Ohio Universities
College of Medicine
4209 St. Rt. 44, P.O. Box 95
Rootstown, Ohio 44272-0095
Phone: (330) 325-6639
Fax: (330) 325-5916
Email: ssivaram@neoucom.edu
Auditory Neuroscience Research Focus Group
Synaptic Transmission and Neural Circuits Laboratory
Department of Neurobiology

Education:

Professional Experience:

Research Interests:

We are interested in determining the criteria that sensory nuclei use to decide which incoming stimulus to enhance and which to suppress, and how a neural network maximizes the information between the input (e.g. an auditory stimulus) and the output (the neural response). The number of neurons activated by an input, the balance between excitation and inhibition, and intrinsic membrane properties and local circuitry, limit the amount of information that can be conveyed by the network about the input, and the maximization of the output becomes a complex task.

Our laboratory focuses primarily on the inferior colliculus, an auditory midbrain nucleus. The organization of the inferior colliculus and its importance to auditory function make it an excellent model system to address the functional importance of intrinsic membrane properties, synaptic transmission and network organization in controlling excitability. In particular, we are examining the characteristics of inputs and how they change with stimulus strength and frequency, and the role of voltage-gated ion channels and local circuitry in shaping neuronal responses to changing inputs.

To understand how the inferior colliculus functions, we examine the constraints imposed on response patterns by a basic circuit defined in terms of cell types and connections. Important elements of the circuit include 1) parallel excitatory and inhibitory inputs to the central nucleus of the inferior colliculus; 2) local circuitry contained within single (iso-frequency) laminae of the central nucleus; 3) inter-laminar circuitry (cross-frequency connections) within one colliculus, and 4) commissural connections between the two colliculi.

Our primary experimental model is the rat brain slice. We stimulate inputs to the inferior colliculus through the lateral lemniscus, and simultaneously record activity in identified neurons with the whole-cell patch clamp technique, and in neuronal populations with voltage-sensitive dyes; this allows us to link specific cell types with spatio-temporal activity patterns.

Two slice planes are used. The laminar slice plane, cut parallel to IC laminae, allows the study of circuits within an iso-frequency lamina. The transverse slice plane, cut across laminae, allows the study of inter-laminar, cross-frequency circuitry within one colliculus, as well as inter-collicular connections.

Selected Publications:

• Peruzzi, D, Sivaramakrishnan, S. & Oliver, D. L. (2000) Identification of cell types in brain slices of the inferior colliculus. Neuroscience, Vol 101 (2):403-416.

• Sivaramakrishnan, S. & Oliver, D. L. (2001) Distinct K currents result in physiologically distinct cell types in the inferior colliculus of the rat. J. Neuroscience, Vol 21(8):2861-2877.

• Wu, S-H, Ma, C-L, Sivaramakrishnan, S. & Oliver, D. L. (2002). Synaptic modification in neurons of the central nucleus of the inferior colliculus. Hearing Research, 3904:1-12.

• Sivaramakrishnan, S., Sterbing-D'Angelo, S. J., Filipovic, B., D'Angelo, W. R., Oliver, D. L. and Kuwada, S. (2004). The effect of inhibition on rate-level functions in neurons of the mammalian inferior colliculus. J. Neurosci. 24(21):5031-5043.

• Sivaramakrishnan, S. & Oliver, D. L. (2006) Neuronal responses to lemniscal stimulation in laminar brain slices of the inferior colliculus. J Assoc Res Otolaryngol. 2006 Mar 7(1):1-14.