Plasticity in the Mediodorsal Thalamo-Prefrontal Cortical Transmission in Behaving Mice

Cyril Herry, Rose-Marie Vouimba, René Garcia
Journal of Neurophysiology. 1999-11-01; 82(5): 2827-2832
DOI: 10.1152/jn.1999.82.5.2827

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We studied changes in thalamo-prefrontal cortical transmission in behaving mice
following both low-frequency stimulation of the mediodorsal thalamus (MD) and
during extinction of a conditioned fear response. Electrical stimulation of the
MD induces a field potential in the medial prefrontal cortex (mPFC) characterized
by two initial negative-positive complexes (N1-P1 and N2-P2) followed by two
positive-negative complexes (P2-N3 and P3-N4). The N1-P1 and N2-P2 complexes were
identified as resulting from orthodromic and antidromic prefrontal activation,
respectively. Because the two complexes were not often easily dissociated,
plasticity in the prefrontal synaptic transmission was considered to result from
changes in N1-P2 amplitude. Low-frequency thalamic stimulation (1, 200 pulses at
2 Hz) produced either long-term (at least 32 min) depression or potentiation of
the N1-P2 amplitude. Mice submitted to fear conditioning (tone-shock
association), displayed on the first day of extinction (tone-alone presentations)
a strong freezing behavior, which decreased progressively, but was still high the
following day. Extinction of conditioned fear was accompanied the first day by a
depression of prefrontal transmission, which was converted into potentiation the
following day. Potentiation of prefrontal transmission lasted at least 24 h
following the second day of the fear extinction procedure. In conclusion,
low-frequency thalamic stimulation can produce, in behaving mice, either
depression or potentiation of prefrontal synaptic transmission. Decrease in
prefrontal synaptic transmission observed during the first day of extinction may
reflect processing of the high degree of predictiveness of danger (unconditioned
stimulus: US) by the aversive conditioned stimulus (CS). However, the subsequent
potentiation of transmission in the mPFC may be related to processing of
cognitive information such as the CS will no longer be followed by the US, even
if emotional response (freezing) to the CS is still high.

DOI: 10.1152/jn.1999.82.5.2827
PMID: 10561450 [Indexed for MEDLINE]


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