Related Experiment Videos
Plasticity in the mediodorsal thalamo-prefrontal cortical transmission in behaving mice
C Herry1, R M Vouimba, R Garcia
1Laboratoire de Neurosciences Cognitives, Centre National de la Recherche Scientifique Unité Mixte de Recherche 5807, Université de Bordeaux I, 33405 Talence, France.
Abstract:
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.
Insights
Low-frequency stimulation of the mediodorsal thalamus (MD) in mice induced either depression or potentiation of thalamo-prefrontal cortical transmission. Fear extinction also altered this transmission, showing initial depression followed by long-lasting potentiation.
Area of Science:
- Neuroscience
- Synaptic Plasticity
- Fear Memory
Background:
- Thalamo-prefrontal cortical pathways are crucial for cognitive functions.
- Understanding synaptic plasticity in these pathways is key to deciphering learning and memory processes.
- Fear conditioning and extinction involve complex neural circuit modifications.
Purpose of the Study:
- To investigate the effects of low-frequency stimulation of the mediodorsal thalamus (MD) on thalamo-prefrontal cortical transmission in behaving mice.
- To examine changes in prefrontal synaptic transmission during the extinction of conditioned fear responses.
- To characterize the plasticity of the N1-P2 amplitude in the medial prefrontal cortex (mPFC) following MD stimulation and fear extinction.
Main Methods:
- Electrical stimulation of the MD to induce field potentials in the mPFC.
- Low-frequency stimulation protocol (1,200 pulses at 2 Hz) applied to the MD.
- Fear conditioning using tone-shock association followed by extinction trials (tone-alone presentations).
- Measurement of N1-P2 amplitude changes in the mPFC to assess synaptic plasticity.
Main Results:
- Low-frequency MD stimulation induced either long-term depression or potentiation of the mPFC N1-P2 amplitude (lasting at least 32 min).
- During the first day of fear extinction, a depression of prefrontal transmission was observed.
- On the second day of extinction, this transmission shifted to potentiation, lasting at least 24 hours.
Conclusions:
- Low-frequency thalamic stimulation can bidirectionally modulate prefrontal synaptic transmission in behaving mice.
- Initial depression of mPFC transmission during fear extinction may reflect the processing of a highly predictive aversive stimulus.
- Subsequent potentiation suggests a role in processing the cognitive shift that the conditioned stimulus no longer predicts an aversive outcome.