Carvell, PhD, PTUniversity
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
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.
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.