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George E. Carvell, PhD, PT   University of Pittsburgh
 
LOCAL POTENTIALS VIII: Inhibitory Control 2 “Life is hard enough, your will should not be preoccupied with calming an endless storm of electrochemical chaos” GEC ‘01
Inhibitory synapses have a key role in controlling levels of neuronal excitability. The amount of neuronal activity can be measured at the cellular, metabolic level. Glucose is the major source of energy for neurons. Radioactively labeled glucose: 2-Deoxy-glucose (2DG) can be measured at the level of single cells in the brain. If a rat is actively exploring its environment, the brain will ‘light-up’ in those areas that are most metabolically active. One such area is the whisker representation in the somato-sensory ‘barrel’ cortex since rats use their whiskers to explore and engage their environment. When 2DG label is quantified, it has been shown that the most active neurons are GABAergic (inhibitory neurons) in the barrel cortex (see GAD+2DG in fig 13) despite the fact that inhibitory neurons represent only a small fraction of the total number of neurons found there (see fig 10). GAD is an enzyme found in GABAergic neurons (fig 6.16), so GAD+ = presumed inhibitory neurons and GAD- = presumed excitatory neurons. Thus, the few inhibitory neurons are very active and provide the necessary control to reduce the total excitatory activity of the brain- a critical factor in preventing an overload of circuits that could lead to a ‘blackout’ or worse in the brain.
J.S. McCasland and L.S. Hibbard, GABAergic Neurons in Barrel Cortex Show Strong, Whisker-Dependent Metabolic Activation During Normal Behavior. J Neurosci 17: 5509-            5527, 1997.
= INHIBITORY NEURONS (GAD+)
= EXCITATORY NEURONS (GAD-)
Fig 10,
p 5523
Fig 13,
p 5525
BC&P Fig 6.16  p 146
GAD converts Glu to GABA in Inhib. Neurons
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