The Journal of Neuroscience, July 15, 2001, 21(14):4969-4976
Predominance of Late-Spiking Neurons in Layer VI of Rat
Perirhinal Cortex
John P.
McGann1,
James
R.
Moyer Jr2, and
Thomas H.
Brown1, 2, 3
1 Interdepartmental Neuroscience Program and
Departments of 2 Psychology and 3 Cellular and
Molecular Physiology, Yale University, New Haven, Connecticut 06520
Recent work demonstrated the importance of perirhinal cortex (PR)
in a variety of behavioral tasks and disease processes. Studies from
our laboratory revealed that some layers of PR contain neurons with
unusual properties. Here we report a detailed examination of the
cellular neurobiology of layer VI of PR, using whole-cell recordings
and biocytin cell fills in horizontal rat brain slices. The most
striking finding is that an overwhelming majority (~86%) of neurons
are late-spiking (LS) cells, which can delay the onset of their spike
trains by several seconds or more relative to the onset of a
depolarizing current step. LS neurons previously have been shown
to exist only in very small numbers in a limited number of other
cortical regions. Anatomical reconstructions have revealed that the LS
neurons vary greatly in morphology, including both pyramidal and
nonpyramidal cells. Another surprising physiological finding is the
fact that single-spiking (SS) neurons are the second most common cell
type (~7%). SS neurons issue only a single action potential even in
response to extreme depolarization. They have been seen previously in
the amygdala, but never in cortex. A third remarkable finding is that
there are almost no regular spiking (RS) neurons, unlike all
other cortical regions that have been studied. This unique abundance of
LS neurons in layer VI, along with the presence of SS neurons and the
absence of RS neurons, demonstrates that layer VI of PR is unlike any
other cortical region that has been studied to date.
Key words:
perirhinal; amygdala; late spiking; temporal cortex; slowly inactivating; timing; classical conditioning; entorhinal; morphology; delay; pyramidal; nonpyramidal
Copyright © 2001 Society for Neuroscience 0270-6474/01/21144969-08$05.00/0