Role Of Medial Prefrontal Cortex During Trace Eyeblink Conditioning In Guinea Pigs And The Underlying Mechanisms

Aim and method:Associative motor learning is critical for working and sport activities. Trace eyeblinkconditioning (TEBC) is an experimentally tractable model of associative motor learningwhich provides exciting chances for studying the interactions among distributed brainsystems. Typically, this paradigm of conditioning involves paired presentations of a neutralconditioned stimulus and a reinforcing unconditioned stimulus, which are separated by astimulus-free interval.Previous researches have demonstrated the involvement of medial prefronral cortex(mPFC) and cerebellum in TEBC. The current question is what the role of mPFC is duringcerebellum-dependent TEBC and the underlying mechanisms. Thus, the aims of the currentstudy are:(1) to determine whether the mPFC controls cerebellum-dependent associativemotor learning through its persistent outputs and examine how the persistent outputs areinvolved in differential paradigms of eyeblink conditioning by in vivo microstimulation andreversible inactivation;(2) by simultaneously recording local field potential (LFP) signalsfrom the mPFC and the cerebellum in guinea pigs during TEBC, to test whether oscillationsin the theta range between the mPFC and the cerebellum are synchronized and whethertheta-band oscillation synchronization between the mPFC and the cerebellum is contributedto the performance of trace conditioning response (CR);(3) by recording LFP from themPFC in guinea pigs during TEBC, to test whether spontaneous mPFC theta activity willinfluence subsequent acquisition and/or performance of trace CRs.Results:(1) The role of persistent outputs from the mPFC to the cerebellum for the acquisitionand expression of trace CRs.1) After7days trace interval switch training, the guinea pigs showed the double-peak trace CRs.2) Microinjections of the muscimol (1.25μg) into intermediate cerebellum preventedthe expression of both CR1and CR2; whereas bilateral microinjections of the muscimol(1.25μg) into the mPFC prevented the expression of CR2, rather than CR1;3) The guinea pigs that received the850-ms mPFC stimulation learned robust eyeblinkresponses, in comparison with the350-ms mPFC-stimulation and the complex mPFC-stimulation guinea pigs. When merged eyeblink responses in stage2with the CR1evokedby the tone CS, the850-ms mPFC-stimulation guinea pigs seemed to exhibit bimodal-likeCRs;4) The guinea pigs that receive850-ms mPFC electrical stimulation and100ms airpuffstimulation with a500ms trace interval showed on obvious eyeblink responses during stage2;5) Microinjections of muscimol (1.25μg) into the right lateral portion of pontine nuclei(LPN) prevented the expression of CR2-like responses;6) The placement of cannula tips in the faster extinction group animals was verified inthe anterior/middle part of right LPN, whereas in the slower extionction group animals wasverified in the middle/posterior part of right LPN;7) Bilateral microinjections of SOCP (10μg) into the mPFC prevented the expressionof CR2, whereas bilateral microinjections of D-APV (10μg) into the mPFC showed nosignificant effects on the expression of CR2.(2) The contribution of theta-band coherence between mPFC and the cerebellum to theacquisition and expression of trace CRs.1) Obvious oscillation syncronizaiton between the mPFCand the cerebellum wasobserved during the trace interval, which predominantly peaked in the theta range.2) Stronger mPFC-cerebellum theta-band synchronization was observed in theadaptive learners. Additionally, the stronger theta-band coherence in the adaptive learnerswas attributed to temporal alignment of the mPFC and the cerebellum theta-rhythmic neuralactivities, rather than correlated fluctuations in power;3) The association of adaptive CR performance with the mPFC-cerebellum theta-bandsynchrony was specially occurred in the early-learning stage;4) Microinjections of SB334867(1.6μg) into the intermediate cerebellum significantly decreased the mPFC-cerebellum coherence in theta-frequency band, accompanied by theimpaired performance of adaptive trace CRs;(3)The correlation between spontaneous mPFC theta oscillations and the acquisitionand expression of trace CRs.1) The baseline mPFC theta activity did not contribute to the subsequent acquisition oftrace CRs;2) During the well-learning stage, the trace CRs occurred in the trial with the baselinemPFC theta activity tended to be more adaptive;3) There was no significant relationship between the trace interval theta activity in themPFC and the performance of trace CRs;4) There was no significant relationship between the baseline mPFC theta activity andthe performance of CRs during TEBC with a100-ms trace interval.Conclusion：(1) Persistent outputs from the caudal mPFC to the cerebellum are necessary for theacquisition and expression of trace CRs;(2) There is obvious theta-band oscillation synchronization between the mPFC and thecerebellum during TEBC. Importantly, the adaptive trace CRs were performed specificallywhen the theta coherence was higher. Moreover, both the mPFC-cerebellum theta coherenceand the adaptive CR performance were impaired in a positively correlated manner after thedisruption of endogenous orexins in the cerebellum;(3) The baseline spontaneous theta oscillations in the mPFC are correlated with the CRperformance in the late, rather than the early stage of associative motor learning.