A COMPARISON OF HIPPOCAMPAL CA1 AND CA3 BURST PROPERTIES IN BEHAVING ANIMALS' E' J' Markus,1 J' Trop

1
A COMPARISON OF HIPPOCAMPAL CA1 AND CA3 BURST
PROPERTIES IN BEHAVING ANIMALS. E. J. Markus,1
J. Tropp1, J. J. Chrobak1, M. C. Quirk2, J. A.
Oler1. 1Psych. Dept., Behav. Neurosci. Div., Univ
of Conn., Storrs, CT 2Cold Spring Harbor
Laboratories, Cold Spring Harbor, NY.
1007.9
ABSTRACT
HIPPOCAMPAL CIRCUITRY
BURST PROPERTIES CA1 versus CA3
EFFECT OF BEHAVIORAL STATE
In order to know how the hippocampus functions
one must understand the inter-relations among its
different components, such as differences between
CA1 and CA3 pyramidal neurons. There are a
number of anatomical and basic physiological
differences between neurons in these two regions.
However, little is known about how these
differences influence burst discharge in
freely-behaving rats. The present study examined
differences between CA1 and CA3 during two
behavioral states (theta and awake immobility).
Female Sprague-Dawley rats were trained to
alternate on a U shaped runway for food
reinforcement. Single unit recordings of
hippocampal CA1 and CA3 cells were conducted in
rats at rest on a holder and while running on the
maze. CA3 cells showed larger spikes, more
spike amplitude attenuation, had a greater
average number of spikes in a burst, and a
shorter inter-spike interval. There was no
difference in tendency to burst between CA1 and
CA3 cells. Behavioral state also affected
firing. When the animals were at rest, cells had
higher amplitude peaks and tended to burst more
than when they were running on the maze. Notably,
CA1 cells were more affected by the behavioral
state of the animal than CA3 cells. The data
indicate important differences between CA1 and
CA3 and these differences have theoretical
implications with regard to (1) the relationship
between connectivity and physiological firing
characteristics (2) segregation of function
within the hippocampus. Supported by NSF IBN
9809958 NIH R29-A613941-01A1 (Markus)
AVERAGE SPIKES IN BURST
BURSTINESS
RATIO OF BURST EVENTS TO SS EVENTS
Plt0.01
Plt0.001
CA1 r.58, plt.001 CA3 r.61, plt.001
CA1 r.52, plt.001 CA3 r.60, plt.001
INTERSPIKE INTERVAL
Behav. Plt0.01 Interaction Plt0.01
Behav. Plt0.001 Interaction Plt0.01
Surgery Animals were implanted with a miniature
recording device to allow for extracellular
single unit recordings. Each microdrive
contained four movable tetrode recording probes.
A comparison of the recording signal from each
electrode allowed for a differentiation of the
firing of one cell from another. Recording
Procedure Animals wore a multi-channel headstage
device that contained two arrays of infrared
light emitting diodes. During the recording
session, the animals were connected to the
recording apparatus by a fine wire bundle. An
overhead video tracking system provided
information about the rat's location and head
direction. An analysis of the multi-single unit
recordings from each probe was conducted off-line
using a spike parameter clustering method
(McNaughton et al., 1989 Mizumori et al., 1989).
The clustering was based on the relative
amplitudes of the signals and the spike durations
(Wilson McNaughton, 1993). During analysis a
velocity filter was used to assure that all of
the data collected was taken only if the animal
moved faster than 2.0 cm/sec. After
surgery, animals were re-trained on the
alternation task in the recording room. Data
were collected in two stages HOLDER DATA
Approximately ten minutes of recordings of
cells were obtained while the animal sat quietly
on a small platform outside the maze room.
MAZE RUNNING DATA This was followed by 40
alternations on the maze. The total recording
session lasted less than 30 minutes.
INTRODUCTION
Plt0.05
Plt0.001
Hippocampal pyramidal cells exhibit
place-specific discharge in relation to the
location of the animal (O'Keefe Dostrovsky,
1971). CA1 and CA3 pyramidal place cells 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). Both CA1 and CA3 pyramidal
neurons exhibit burst discharges during both
locomotion associated with hippocampal theta, as
well as during immobility and slow-wave sleep
when the hippocampus exhibits sharp wave bursts
(Buzsaki, 1989). Data however are quite limited
about differences in the burst characteristics
across behavioral states and between the CA3 and
CA1 sub-region. Further, CA3 and CA1 pyramidal
neurons have distinct cellular properties and
receive quite distinct inputs. The present
study examined differences in the bursting
properties of CA1 and CA3 neurons within the
hippocampus in awake-behaving rats across
distinct behavioral states awake immobility and
maze performance.
AVERAGE SPIKES IN BURST
.
CA1 r.08, pgt.1, n.s. CA3 r.23, pgt.1, n.s.
CA1 r.42, plt.01 CA3 r.29, pgt.1, n.s.
frequency
Behav. Plt0.001 Interaction N.S.
Behav. Plt0.05 Interaction N.S.
AMPLITUDE OF SINGLE SPIKE
AMPLITUDE OF FIRST SPIKE IN BURST
Are there differences in the bursts
characteristics of CA3 and CA1 neurons as a
function of behavioral state?
CA1 r.88, plt.001 CA3 r.95, plt.001
CA1 r.93, plt.001 CA3 r.98, plt.001
Behav. Plt0.01 Interaction N.S.
Behav. Plt0.01 Interaction N.S.
DATA ANALYSIS BURST PROPERTIES

• CA3 neurons exhibited more spikes per burst,
  greater spike frequency, and larger amplitude
  spikes than CA1 neurons.
• However, there were no differences between CA3
  and CA1 neurons in their tendency to burst or
  duration of burst.

METHODS

• A burst was defined as a spike having an
  interspike interval less than 10 ms.
• The data were examined in two stages
• I. Examination of the characteristics between CA1
  and CA3 bursts and single spikes independent of
  behavioral state.
• II. A within-cell examination of the effects of
  behavioral state and whether and how they
  interact with bursts within each subregion (CA3
  vs. CA1)

Subjects Thirteen female (approximately
6-8months of age) Sprague-Dawley rats (Harlan
Sprague-Dawley, IN) were used in the experiment.
Rats were singly housed in transparent plastic
tubs, in a room with a 1212-h light dark cycle.
All animals were food deprived to 95 of their ad
libitum weights (Tropp Markus, 2001) and
trained to alternate for pellet reinforcement.

• CA1 neurons exhibit significantly less
  burstiness during maze running than CA3
  neurons, while bursting as often as CA3 neurons
  during awake immobility.
• CA1 neurons are more sensitive to changes in
  behavioral state than CA3 neurons.

SPIKE AMPLITUDE ATTENUATION
CA1 r-.08, pgt.1, n.s. CA3 r .26, pgt.1, n.s.
HISTOLOGY
REFERENCES
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• CA3 neurons exhibited more spike amplitude
• attenuation than CA1 neurons.