Medial prefrontal cortex TRPV1 channels modulate the baroreflex cardiac activity in rats.

BACKGROUND AND PURPOSE: The ventral portion of the medial prefrontal cortex (vMPFC) comprises the infralimbic (IL), prelimbic (PL) and dorsopenducular (DP) cortices. The IL and PL regions facilitate the baroreceptor reflex arc. This facilitatory effect on the baroreflex is thought to be mediated by vMPFC glutamatergic transmission, through NMDA receptors. The glutamatergic transmission can be modulated by other neurotransmitters, such as the endocannabinoids, which are agonists of the TRPV1 receptor. TRPV1 channels facilitate glutamatergic transmission in the brain. Thus, we hypothesized that TRPV1 receptors in the vMPFC enhance the cardiac baroreflex response. EXPERIMENTAL APPROACH: Stainless steel guide cannulae were bilaterally implanted into the vMPFC of male Wistar rats. Afterwards, a catheter was inserted into the femoral artery, for recording MAP and HR, and into the femoral vein for assessing baroreflex activation. KEY RESULTS: Microinjections of the TRPV1 receptor antagonists capsazepine and 6-iodo-nordihydrocapsaicin (6-IODO) into the vMPFC reduced the cardiac baroreflex activity in unanaesthetized rats. Capsaicin microinjected into the vMPFC increased the cardiac baroreflex activity in unanaesthetized rats. When an ineffective dose of the TRPV1 receptor antagonist 6-IODO was used, the capsaicin-induced increase in the cardiac baroreflex response was abolished. The higher doses of capsaicin administered into the vMPFC after the ineffective dose of 6-IODO displaced the dose-response curve of the baroreflex parameters to the right, with no alteration in the maximum effect of capsaicin. CONCLUSIONS AND IMPLICATIONS: The results of the present study show that stimulation of the TRPV1 receptors in the vMPFC increases the cardiac baroreceptor reflex response.

The object pattern separation (OPS) task: a behavioral paradigm derived from the object recognition task.

The object recognition task (ORT) is widely used to measure object memory processes in rodents. Recently, the memory process known as pattern separation has received increasing attention, as impaired pattern separation can be one of the cognitive symptoms of multiple neurological and psychiatric disorders. Pattern separation is the formation of distinct representations out of similar inputs. In the search for an easily implemented task for rodents that can be used to measure pattern separation, we developed a task derived from the ORT and the object location task (OLT), which we called the object pattern separation (OPS) task. This task aims to measure spatial pattern separation per se, which utilizes memory processes centered in the DG and CA3 region of the hippocampus. Adult male C57BL/6 mice and adult male Wistar rats were used to validate different object locations which can be used to measure spatial pattern separation. Furthermore, different inter-trial time intervals were tested with the most optimal object location, to further evaluate pattern separation-related memory in mice. We found that specific object locations show gradual effects, which is indicative of pattern separation, and that the OPS task allows the detection of spatial pattern separation bi-directionally at intermediate spatial separations. Thus, object locations and time intervals can be specifically adjusted as needed, in order to investigate an expected improvement or impairment. We conclude that the current spatial OPS task can be best described as a specific version of the ORT, which can be used to investigate pattern separation processes.