Molecular Mechanisms of Synapse Development and Plasticity

National Institute Of Mental Health

Investigators

Linked publications & trials

Abstract

1. Regulation of spine plasticity in proximal and distal dendrites. Experience-dependent modification of synapses, the brain’s cellular substrate for learning and memory,(such as caspases and autophagy) for NMDA receptor-dependent long-term depression (NMDAR-LTD). Our previous work demonstrates that the uneven distribution of autophagosomes in dendrites underlies the distinct inducibility of NMDAR-LTD in proximal and distal parts of the To investigate this question, we conducted 3D neuron reconstruction to analyze the volume, density, and subtype proportions of spines. To probe the role of long-term depression and autophagy in structural plasticity, we utilized caspase-3 and ATG5 knockout mice with known deficits in NMDAR-LTD and autophagy. ATG5 knockouts, but not caspase-3 knockouts, have larger spines in distal dendrites than do proximal dendrites. Both caspase-3 and ATG5 knockout mice have increased spine volume in all three spine subtypes: thin, stubby, and mushroom. ATG5 knockout mice had less spine density than controls. Both caspase-3 and ATG5 knockout mice exhibited redistribution of spine subtype, with reduced proportions of thin subtype and increased proportions of stubby and mushroom subtypes. These findings indicate that disrupting autophagy and caspase-3 alters spine volume and subtype morphology, while disrupting autophagy alters spine volume differently in proximal and distal dendrites. 2. Establish a protocol for preparing mouse hippocampal slices for ex vivo recordings of the temporoammonic pathway (TAP). This pathway consists of direct projections from the entorhinal cortex to distal dendrites of hippocampus CA1. With inputs traveling directly from the entorhinal cortex to the hippocampus, TAP provides an important model structure for investigating synaptic plasticity. While the ability of the TAP to modulate hippocampal output is established, ex vivo electrophysiological characterization requires a specific preparation to preserve the input. To conduct extracellular recordings of TAP inputs, we established a protocol for preparing TAP containing ex vivo slices from mice. We published a protocol paper that describes the specific slicing plane, an angled horizontal slice preparation, along with anatomical hallmarks for the identification of stimulation and recording electrode placement. We additionally described techniques to verify TAP electrical stimulation via pharmacological and optogenetic manipulations. Our protocol allows for electrophysiological assessment of TAP ideally suited for investigations centered around long-term plasticity, made possible by our improved extracellular recording paradigm. The slicing paradigm for preserving and selectively stimulating the TAP can also be applied to whole-cell recording applications and can also be readily adapted to other rodent models, such as rat or prairie vole. 3. Characterize the Brain Circuitry and Neural Activity Mediating Frustration. Omission of expected reward can induce an aversive emotion—known as frustrative nonreward (FNR)—which can influence subsequent behavior and physiology. FNR is an integral mediator of irritability, motivation, anxiety, learning, and social behavior. Aberrant response to FNR is a core feature of irritability, which is an impairing symptom especially prevalent in youth, where it is a common reason for psychiatric assessment and treatment. Irritability is also present in many psychiatric disorders, including disruptive mood dysregulation disorder (DMDD), oppositional defiant disorder, intermittent explosive disorder, attention-deficit/hyperactivity disorder, autism spectrum disorder, bipolar disorder, major depressive disorder, and anxiety disorders in both youth and adults. Despite the significant public health impact of irritability, little is known about its brain mechanism, and there are no FDA-approved treatments outside the context of autism. To facilitate the search for neural mechanisms of frustration and novel treatments for irritability in youth, we designed a human frustration task and developed a human study protocol (NCT06484088) to analyze the participant’s brain activity during the frustration task with magnetoencephalography. To date, we have been enrolling healthy volunteers and conducting MEG recording. This work will lay a foundation for future research on the neural mechanism of FNR and irritability.