Involvement of CRFergic neurotransmission in the functional lateralization of the medial Prefrontal Cortex (mPFC) in the cardiovascular and behavioral responses observed in the contextual fear conditioning model

Abstract

The medial prefrontal cortex (mPFC) is a limbic structure involved in the expression of physiological and behavioral responses to conditioned aversive stimuli, including those evoked by contextual fear conditioning (CFC). However, the local neurochemical mechanisms in the mPFC involved in controlling the responses to CRC are still poorly understood. In this sense, the presence of peptides from the corticotropin-releasing factor (CRF) system in gabaergic interneurons and axon terminals, as well as the CRFergic receptors, have been reported within the mPFC. Despite the evidence that aversive stimuli activate CRF-expressing neurons and increase the local release of CRF within the mPFC, a role of this neurochemical mechanism in the control of cardiovascular and freezing responses to CFC by mPFC has never been reported. Thus, a first hypothesis to be investigated in the present study is that the control of cardiovascular and freezing responses to CFC by the mPFC is mediated by local CRFergic neurotransmission. Another relevant aspect regarding the mPFC is the evidence of a functional lateralization in the control of responses to aversive stimuli. In this sense, results from previous studies indicated that the right mPFC (RmPFC) is more directly related to the control of physiological and behavioral responses during stressful situations, whereas the left mPFC (LmPFC) seems to have a counter-regulatory role inhibiting the RmPFC. Despite these pieces of evidence, a possible lateralization in the control of CFC responses by the mPFC has never been evaluated. In this sense, a second hypothesis to be tested in the present study is that the control of freezing and cardiovascular responses to CFC by the mPFC is lateralized. We will also evaluate the role of CRFergic neurotransmission in a possible lateralized control of the responses to CFC by the mPFC. A lateralization in the morphological consequences within the mPFC resulting from chronic exposure to stressful stimuli has also been reported, so that the LmPFC seems to be more affected. It is also well described in the literature that exposure to chronic stressors before training in conditioning models increases fear memory and, consequently, conditioned defensive responses. Although the involvement of mPFC CRFergic neurotransmission in influence of chronic stress on conditioned aversive responses has never been reported, the hypothesis of an involvement of this neurochemical mechanism of the mPFC is supported by a recent report that the increase in conditioned freezing response in animals submitted to a protocol of chronic variable stress (CVS) was accompanied by an increase in CRF1 receptor mRNA in the mPFC. Thus, a final hypothesis to be investigated is that CRFergic neurotransmission in the mPFC is involved in local morphological changes and in facilitated responses to CFC resulting from previous exposure to an ECV protocol, and this participation is lateralized. In view of the above-mentioned information, the aims of this proposal are: (1) to investigate whether the control of freezing and cardiovascular responses to CFC by the mPFC is lateralized; (2) to characterize the role of CRFergic neurotransmission in the mPFC in control of freezing and cardiovascular responses to MCC; and investigate whether this control is lateralized; and (3) to evaluate the involvement of CRFergic neurotransmission in the mPFC in local morphological changes and in changes on freezing and cardiovascular responses to MCC evoked by previous exposure to an ECV protocol; and assess whether these effects are lateralized. (AU)