The Journal of Neuroscience, September 15, 2002, 22(18):8238-8250
Serotonergic Modulation of Supragranular Neurons in Rat
Sensorimotor Cortex
R. C.
Foehring3,
J. F. M.
van Brederode1, 2,
G. A.
Kinney1, 2, and
W. J.
Spain1, 2
1 Department of Neurology, University of Washington,
Seattle, Washington 98195, 2 Department of
Neurology, Veterans Affairs Medical Center, Seattle, Washington
98108, and 3 Department of Anatomy and Neurobiology,
University of Tennessee, Memphis, Memphis, Tennessee 38163
Numerous observations suggest diverse and modulatory roles for
serotonin (5-HT) in cortex. Because of the diversity of cell types and
multiple receptor subtypes and actions of 5-HT, it has proven difficult
to determine the overall role of 5-HT in cortical function. To provide
a broader perspective of cellular actions, we studied the effects of
5-HT on morphologically and physiologically identified pyramidal and
nonpyramidal neurons from layers I-III of primary somatosensory
and motor cortex. We found cell type-specific differences in response
to 5-HT. Four cell types were observed in layer I: Cajal Retzius, pia
surface, vertical axon, and horizontal axon cells. The physiology of
these cells ranged from fast spiking (FS) to regular spiking (RS). In
layers II-III, we observed interneurons with FS, RS, and late spiking
physiology. Morphologically, these cells varied from bipolar to
multipolar and included basket-like and chandelier cells. 5-HT
depolarized or hyperpolarized pyramidal neurons and reduced the slow
afterhyperpolarization and spike frequency. Consistent with a role in
facilitating tonic inhibition, 5-HT2 receptor activation
increased the frequency of spontaneous IPSCs in pyramidal neurons. In
layers II-III, 70% of interneurons were depolarized by 5-HT. In layer
I, 57% of cells with axonal projections to layers II-III (vertical
axon) were depolarized by 5-HT, whereas 63% of cells whose axons
remain in layer I (horizontal axon) were hyperpolarized by 5-HT. We
propose a functional segregation of 5-HT effects on cortical
information processing, based on the pattern of axonal arborization.
Key words:
5-HT; interneuron; potassium; cortex; pyramidal cell; biocytin
Copyright © 2002 Society for Neuroscience 0270-6474/02/22188238-13$05.00/0
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