Awake Electrophysiological Profiling of the Ventromedial Prefrontal Cortex in a Mouse Model of Depression and Parkinson's Disease.

While Parkinson's disease (PD) is primarily known as a motor disorder, non-motor symptoms often emerge before motor deficits and significantly impact disease progression, being crucial at all disease stages. Among these, depression and anxiety are the most prevalent symptoms and cause a higher symptom burden in women than in men. Alterations in the serotonergic (5-HT) system are frequently linked to mood disorders, and accumulations of α-synuclein (α-Syn) have been observed in the 5-HT raphe nuclei (RN) of patients with Parkinson's disease (PD) and depression. Understanding the neural circuits underlying these non-motor symptoms is therefore critical. Here, we present an improved protocol to investigate the role of the ventromedial prefrontal cortex (vmPFC)-dorsal raphe nucleus (DR) circuit in PD-associated mood disorders using a female mouse model overexpressing the mutant A53T form of human α-syn (h-α-Syn) in the DR. Our method allows high-resolution assessment of neuronal activity in the infralimbic (IL) and prelimbic (PL) cortices under both basal conditions and during aversive conditioning and extinction. Using a tone-light sensory conditioning paradigm in awake, head-fixed mice, we employ multichannel electrophysiological probes to record neuronal responses. Experiments were conducted in virtual reality corridors, combining a cylindrical treadmill with a dual-screen visual display to maintain behavioral engagement while ensuring precise control of sensory stimuli and recording stability. This protocol builds on the established involvement of the IL and PL cortices in fear conditioning and extinction and provides a robust framework to examine dynamic neural activity in circuits implicated in depressive and anxiety-like behaviors in PD. By enabling simultaneous behavioral and electrophysiological measurements under controlled conditions, this approach offers a powerful tool for elucidating the neurobiological mechanisms of non-motor symptoms in PD and for testing potential interventions.