BURSTING AND OSCILLATING NEURONS OF THE CAT BASOLATERAL AMYGDALOID COMPLEX
IN VIVO : ELECTROPHYSIOLOGICAL PROPERTIES AND MORPHOLOGICAL FEATURES.
Denis Pare, Hans-Christian Pape and Jianming Dong.
Departement de Physiologie, Faculte de Medecine, Universite Laval, Quebec,
(QUE), CANADA, G1K 7P4, Institut fur Physiologie, Medizinische Fakultat, Otto-
von-Guericke-Universit[umlaut]at, D-39120 Magdeburg, Germany.
APStracts 2:0136N, 1995.
SUMMARY AND CONCLUSIONS
1. To characterize the physiological properties of lateral and basolateral
(BL) amygdaloid neurons, intracellular recordings were performed in
barbiturate-anesthetized cats. Morphological identification of recorded cells
was achieved by intracellular injection of neurobiotin. Two types of
physiologically-identified projection neurons were distinguished in the BL and
lateral nuclei. 2. The first type of neurons prevailed in the BL nucleus (80%
of BL cells). Their resting membrane potential (Vm) averaged -66 ¯+ 4.9 mV
(average ¯+ standard error). They generated stereotyped spike doublets or
bursts in response to threshold depolarizing pulses. In most cells,
depolarizing pulses of higher amplitude elicited spike bursts or doublets at a
shorter latency followed by a non-adapting train of single spikes whose
frequency rose with the amplitude of the current pulses. However, 15% of BL
bursting neurons generated repetitive spike bursts or doublets in response to
prolonged depolarizing current pulses. The response of BL bursting neurons to
hyperpolarizing current pulses revealed the presence of slow inward
rectification in the form of a depolarizing sag thus suggesting the presence
of an hyperpolarization-activated current. 3. The second type of neurons
prevailed in the lateral nucleus. Their resting Vm was quite polarized (-74 ¯+
2.85 mV) and they generated slow Vm oscillations (2 to 10 Hz) upon steady
depolarization beyond ¯ -62 mV. The frequency of the oscillation increased
with the amount of depolarizing current. In the majority of cells, analysis of
voltage responses to subthreshold current pulses revealed the presence of
voltage- and time-dependent rectification in the depolarizing direction.
Current pulses that brought the Vm to -65 mV and beyond elicited a voltage
response that reached an early peak and then decayed. Increasing the amplitude
of the pulse decreased the latency of the early peak until it triggered an
action potential. Current-voltage plots demonstrated inward rectification in
the depolarizing direction. At the break of hyperpolarizing current pulses
applied at depolarized levels, the Vm overshot pre-pulse values and generated
one or more oscillatory cycles. 4. An important proportion of bursting and
oscillating neurons (45.8 and 29%, respectively) were physiologically
identified as projection neurons by antidromic invasion from the basal
forebrain, entorhinal cortex or perirhinal cortex. The conduction velocity of
bursting and oscillating neurons estimated from the latency of antidromic
spikes was low ( ¯< 2.5 m/s). 5. Most bursting and oscillating neurons of
the BL nucleus were spiny cells with a pyramidal morphology. Four to eight
dendritic trunks emerged from the apex, base and sides of their triangular
soma. When the plane of the section was not parallel to the dominant dendrite,
these multiple proximal dendrites gave a stellate appearance to the cells.
Oscillating neurons of the lateral nucleus were spiny neurons with a variable
morphology. Cells located close to the external capsule appeared stellate
whereas those located more medially often looked like pyramidal neurons.
6. In light of previous findings, these results suggest that BL bursting
neurons could amplify transient synaptic inputs and, through their axon
collaterals, recruit other BL neurons in a population burst that will be
transmitted to target structures. 7. Considering that the entorhino-
hippocampal circuit displays network oscillations at 3-7 Hz in EEG-activated
states, it is suggested that the predisposition of lateral amygdala neurons to
oscillate in this range of frequency might potentiate coherent network
oscillations in these limbic structures. Such oscillations would favor the
emergence of recurring time windows when synaptic interactions would be
facilitated.
Received 13 January 1994; accepted in final form 20 April 1995.
APS Manuscript Number J32-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 9 May 1995.