EFFECTS OF INTRASEPTAL CARBACHOL ON BURST PROPERTIES OF CA1 PYRAMIDAL NEURONS

1
EFFECTS OF INTRASEPTAL CARBACHOL ON BURST
PROPERTIES OF CA1 PYRAMIDAL NEURONS S. Sava1,2,
G.J. Peters1,3, E.J. Markus1 1Psych. Dept., Univ
of Conn., Storrs, CT 2McLean Hospital/Harvard
Medical School, Belmont, MA 3Psych. Dept., Univ
of Delaware, Newark, DE.
ABSTRACT
HISTOLOGY
EFFECT OF CARBACHOL ON BURST PROPERTIES
EFFECT OF NOVELTY ON BURST PROPERTIES
Single-unit recordings in the hippocampus show
that, like cortical neurons, hippocampal
pyramidal cells can fire single spikes or trains
of high-frequency spikes, commonly called bursts
(Rank, 1973). Hippocampal bursts are often
assumed to have distinct physiological (Pike et
al., 1999 Buzsáki et al., 2002) and/or
computational functions (Lisman, 1997 Kepecs et
al., 2002). The functional significance of bursts
however is not clear. Tropp-Sneider and
colleagues (2006) showed that the degree of CA1
bursting decreased when the animal ran on the
maze compared to being at rest. These data may
not indicate a functional change since bursting
increases during sharp-wave oscillations
(Buzsáki, 1989 Harris et al, 2001 Wong and
Prince, 1978). The cholinergic agonist carbachol
was infused into the medial septum, and
hippocampal CA1 cells were recorded in freely
moving rats in a familiar or novel
environment. Septal activation disrupted the
retrieval of a previously stored hippocampal
place cell representation of a familiar
environment regardless of age. When the
environment was changed, medial septal activation
disrupted the encoding process in young, but
facilitated the encoding of the new information
in aged rats. In contrast, burst properties of
CA1 pyramidal cells were not affected by
intraseptal carbachol. While burst firing was
reduced when the animal was running on the maze,
this was not related to the degree of
environmental novelty or to septal
activation. Supported by UConn FRS445142 NIH
R29-A613941-01A1 to E.J.M.
Carbachol increases hippocampal theta power
during drinking
After all single unit recordings were done, each
rat received a series of 5 carbachol infusions.
The hippocampal theta power was measured while
the rat was drinking, before and after carbachol
administration.
INTRODUCTION
Hippocampal pyramidal cells exhibit
place-specific discharge in relation to the
location of the animal (O'Keefe Dostrovsky,
1971). CA1 pyramidal neurons can fire single
spikes or a fast series of spikes commonly
referred to as a burst. Typically bursts contain
2-6 spikes at short intervals, with a progressive
attenuation in the amplitude of the spikes within
the burst (Ranck, 1973 Quirk and Wilson, 1999
Quirk et al., 2001). Both the burst and
attenuation phenomena have been postulated to
play an important role in information processing
(Lisman, 1997 Quirk et al., 2001). Previous
studies showed that behavioral state can affect
the bursting of CA1 neurons specifically, CA1
neurons have a greater propensity to burst during
awake immobility than during maze running (Harris
al., 2001 Tropp Sneider et al., 2006). The
present study examined differences in the
bursting properties of CA1 neurons in
awake-behaving young and old rats during distinct
behavioral states (awake immobility and maze
performance). We also investigated the effects of
intraseptal carbachol and novelty on the burst
properties of CA1 cells.
EFFECT OF AGE AND BEHAVIORAL STATE
.
Are there differences in the burst properties of
CA1 neurons as a function of behavioral state,
age, or novelty?
GENERAL METHODS
T-test , p 0.024

• Bursting of CA1 cells was not affected by the
  novel configuration.

CONCLUSIONS CA1 neurons burst more during awake
immobility than during maze running. Bursting of
CA1 neurons does not seem to be affected by age,
novelty, or intraseptal carbachol infusion.

• Burst spike train having an interspike interval
  less than 10 ms.
• Within-cell examination of the effects of
  behavioral state, age and novelty
• Average number of spikes in burst
• Burst spike interstimulus interval (ISI)
• Burstiness (proportion of spikes in burst out
  of total number of spikes)
• Attenuation (calculated only for bursts of 3 or
  more spikes)

Summary of recorded cells by rat condition
REFERENCES
T-tests , p lt 0.006 , p 0.06

• On holder, CA1 neurons exhibited higher
  proportion of spikes in bursts bursts had more
  spikes and shorter ISI.
• There were no differences between burst
  properties of neurons recorded from young and old
  rats.

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• Despite altering the place field
  characteristics, carbachol did not affect the
  burst properties of CA1 neurons.
• There was less attenuation on the second run on
  the familiar maze.