The Journal of Neuroscience, December 15, 2000, 20(24):9252-9263
Discharge Profiles of Juxtacellularly Labeled and
Immunohistochemically Identified GABAergic Basal Forebrain Neurons
Recorded in Association with the Electroencephalogram in Anesthetized
Rats
Ian D.
Manns,
Angel
Alonso, and
Barbara E.
Jones
Department of Neurology and Neurosurgery, McGill University,
Montreal Neurological Institute, Montreal, Quebec, Canada H3A 2B4
The basal forebrain ostensibly plays a dual role in the modulation
of cortical activation and behavioral state. It is essential for
stimulating cortical activation in association with waking (and
paradoxical sleep), yet also important for attenuating cortical activation and promoting slow wave sleep. Using juxtacellular recording
and labeling of neurons with Neurobiotin followed by immunohistochemical staining for glutamic acid decarboxylase (GAD), we
studied the discharge properties of identified GABAergic basal forebrain neurons in relation to electroencephalographic (EEG) activity
in urethane-anesthetized rats to determine the part or parts that they
may play in this dual role.
The GABAergic neurons displayed distinct discharge profiles in relation
to somatosensory stimulation-evoked cortical activation. Whereas a
significant minority increased its average discharge rate, the majority
decreased its average discharge rate in association with cortical
activation. Moreover, subgroups displayed distinct discharge patterns
related to different cortical activities, including very regular
high-frequency tonic spiking within a gamma EEG frequency range and
rhythmic cluster spiking within a theta-like frequency range during
cortical activation. During irregular slow EEG activity in absence of
stimulation, one subgroup displayed spike bursts correlated with
cortical slow oscillations. As relatively large in size and also
antidromically activated from the cortex, many GABAergic neurons
recorded were considered to be cortically projecting and thus capable
of directly modulating cortical activity. Subgroups of GABAergic basal
forebrain neurons would thus have the capacity to promote cortical
activation by modulating gamma or theta activity and others to
attenuate cortical activation by modulating irregular slow oscillations
that normally occur during slow wave sleep.
Key words:
juxtacellular labeling; gamma; paradoxical sleep; slow
wave sleep; theta; waking
Copyright © 2000 Society for Neuroscience 0270-6474/00/20249252-12$05.00/0
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