J Neurophysiol (November 1, 2002). 10.1152/jn.00085.2002
Submitted on 7 February 2002
Accepted on 18 July 2002
Rhythmic Properties of Neurons in the Rostral Ventrolateral
Medulla of the Rat In Vitro: Effects of Clonidine
Antonio R.
Granata1,2 and
Morton I.
Cohen2,3
1Department of Psychiatry and
2Department of Physiology, New York Medical
College, Valhalla 10595; and 3Department of
Physiology and Biophysics, Albert Einstein College of Medicine, Bronx,
New York 10461
Granata, Antonio R. and
Morton I. Cohen.
Rhythmic Properties of Neurons in the Rostral Ventrolateral
Medulla of the Rat In Vitro: Effects of Clonidine. J. Neurophysiol. 88: 2262-2279, 2002. The rostral
ventrolateral medulla (RVLM) is thought to be the main central site for
generation of tonic sympathetic activity. In the rat in vitro slice
preparation, we used intracellular recordings to identify different
populations of neurons in the RVLM: 43 spontaneously active neurons
with regular (R) or irregular (I) patterns of spike firing and 10 silent neurons. The degree of regularity was quantified by the
coefficient of variation (CV = SD/mean) of interspike interval durations, as well as by the rhythmic properties of the spike autospectrum and autocorrelation. The distribution of CVs was clustered: R and I neurons were defined as those with CVs 
12% (n = 21) or >12% (n = 22),
respectively. The R-type and I-type neurons resemble the type II and
type I neurons, respectively, which were previously characterized in
the RVLM in vivo as barosensitive and bulbospinal. Both types may be
important in generation of sympathetic tone. Clonidine (1-100 µM)
was applied to 10 R-type neurons and 16 I-type neurons. The firing of
21/26 was depressed to the point of silence. However, 18/26 neurons
were excited earlier in the perfusion. The later depression of firing
occurred in both I and R neurons and in different cases was associated
with either hyperpolarization or depolarization.
