Optical Dissection of the Neural Circuitry Controlling Sensorimotor Gating

The fact that individual mental illnesses can result from a host of diverse genetic and environmental risk factors has made it exceedingly difficult to therapeutically target their underlying causes. One explanation for this ‘many pathways to one disease’ relationship is that the brain region responsible for a given set of symptoms can become disrupted by distinct connections from multiple other brain regions. Thus a better understanding disease-related neural circuitry might explain the many ways the circuitry can be disrupted to yield the same set of symptoms. To address this idea, we will use a viral-genetic approach to optogenetically manipulate or image calcium activity in distinct neuronal populations that project to the brain nucleus that controls sensorimotor gating. Deficits in sensorimotor gating occur in a wide range of diverse neuropsychiatric disorders, suggesting that there are multiple ways for the circuitry controlling the behavior to become disrupted. Sensorimotor gating is readily assessed in rodents by measuring pre-pulse inhibiton (PPI), which tests the ability of a weak, auditory pre-stimulus to attenuate an animal’s acoustic startle response (ASR). The basic neural circuit controlling the ASR is well characterized: the caudal pontine nucleus (PnC) modulates the amplitude of the startle response based on auditory information from the cochlear nucleus. To determine how and which brain regions modulate the ASR and PPI, we will use a retrogradely transported Crerecombinase expressing virus (CAV2-Cre) to selectively express the genetically encoded calcium sensor (GCaMP6) or excitatory/inhibitory opsins (ChR2/NpHR) in neurons that directly project to the PnC. We will then use miniature fluorescence microscopes to image calcium activity in PnC-projecting neurons during acoustic startle and PPI. To establish a causal role for the dynamics we observe in PnC-projecting neurons during PPI, we will also optogenetically manipulate these neurons during acoustic startle and PPI. Our preliminary data reveal two newly discovered direct projections to the PnC, one that is likely excitatory and one that is likely inhibitory. Based on this difference, we hypothesize that these upstream nuclei make opposing contributions to PnC activity and PPI. As these nuclei may contribute to neuropsychiatric symptoms other than PPI, our findings potentially provide novel therapeutic targets for treating diverse neuropsychiatric disorders.