A part of the brain known as the striatum is thought to be important for the planning and modulation of movements. A sparse population of inhibitory interneurons is found across the striatum. These neurons have direct electrical connections with each other through what are known as gap junctions. Gap junctions are composed of proteins that cross the cell membranes of adjoining cells and enable current to flow between them. It’s been suggested that these inhibitory interneurons play a role in oscillatory activity observed in gross electrical activity from the brain region.

The paper “Fast oscillations in cortical-striatal networks switch frequency following rewarding events and stimulant drugs” by Dr. Joshua Berke (published September 2009 in the European Journal of Neuroscience) examines the activity of inhibitory interneurons in the striatum in relation to gross electrical activity from the brain region (local field potentials), behavior, and drugs.

Dr. Berke found correlations between behavioral states and fast oscillations in cortical-striatal circuits. An animal’s striatum switched into high frequency oscillations (70-90Hz; gamma) for a short period of time when it was rewarded. At the single cell level he found inhibitory interneurons firing action potentials in phase with the high frequency oscillations. His observations suggest that high frequency oscillations in the striatum are behaviorally relevant and that inhibitory interneurons may be involved in the circuit generating the high frequency oscillations.

Two drugs that enhance dopamine effects in the striatum (amphetamine and apomorphine) were tested for their influences on oscillatory activity. Both drugs shifted striatum local field potentials to high frequency oscillations (70-90Hz; gamma). They also enhanced behavioral activity.

These data are particularly intriguing since circuits involving the striatum malfunction in Parkinson’s disease. In fact, switching from beta to high gamma (70-85Hz) oscillations has been seen in the brains of Parkinsonian patients after they take L-DOPA, which boosts dopamine in the brain.

Side note: I wonder if dopamine may be acting on the gap junctions between inhibitory interneurons in the striatum? It’s been shown that dopamine applied to the retina results in a decrease in electrical conductance by the gap junctions between amacrine cells.