Dissertation Defense - Carlos Puentes-Mestril
Diversity and mechanisms of state-dependent regulation of synaptic plasticity
Dr. Sara Aton, Chair
The Synaptic Homeostasis Hypothesis (SHY) posits that sleep regulates synaptic strengths through synaptic weakening. Researchers have found structural, molecular, and electrophysiological evidence in support of SHY. However, prior studies have only investigated specific regions of the neocortex while focusing on excitatory synapses. Thus, it’s unclear how inhibitory cell types respond to sleep loss, their role in sleep dependent synaptic weakening, or whether all brain regions undergo sleep dependent weakening. We begin addressing these gaps by using translating ribosome affinity purification (TRAP) and in situ hybridization to characterize the effects of sleep vs. SD on abundance of ribosome-associated transcripts in Camk2a-expressing (Camk2a+) pyramidal neurons and parvalbumin-expressing (PV+) interneurons in mouse hippocampus and neocortex. We find that while both Camk2a+ neurons and PV+ interneurons in neocortex show concurrent SD-driven increases in ribosome-associated transcripts for activity-regulated effectors of plasticity and transcriptional regulation, these transcripts are minimally affected by SD in hippocampus. Similarly, we find that while SD alters several ribosome-associated transcripts involved in cellular timekeeping in neocortical Camk2a+ and PV+ neurons, effects on circadian clock transcripts in hippocampus are minimal, and restricted to Camk2a+ neurons. To interrogate a hypothesized mechanism for state-dependent regulation of synaptic plasticity, we use optogenetics to rhythmically activate Layer 6 corticothalamic neurons in the slow wave activity frequency band during wakefulness and look to see if activity-regulated effectors of plasticity express sleep-like patterns of expression. Taken together, our results indicate that SD effects on transcripts destined for translation are both cell type- and brain region-specific, and that these effects are substantially more pronounced in the neocortex than the hippocampus.