The Effect of Optogenetic Manipulation of SS interneurons within Malformed, Epileptogenic Cortex

A large percentage of individuals with intractable epilepsies have an accompanying cortical malformation, the underlying cellular mechanisms of which are poorly understood. It is known however that in an animal model for one such malformation, polymicrogyria, epileptogenesis occurs most easily from an adjacent area termed the paramicrogyral region (PMR). Previous studies implicate SS interneurons as a potential contributor to this pathology, which lead to our hypothesis: in PMR, SS interneurons exert a higher modulatory influence on excitatory pyramidal cells, as compared to the same by SS interneurons within homologous control cortex. Using a freeze-lesion model for polymicrogyria in transgenic mice that selectively express either Channelrhodopsin or Archaerhodopsin optogenetic channels in these cells, we assessed the contribution of SS interneurons as it potentially differs between layer V of PMR and control cortex. These studies provided the following biological examples in support of previous extrapolations that indicate SS over-activation within PMR: (1) SS interneuron mediated evocation of inhibitory events in layer V excitatory neurons is more robust in PMR than in control. Similarly, electrically-evoked inhibitory events in these excitatory neurons trend towards being larger, signifying a larger contribution by interneurons. (2) SS interneuron mediated suppression of electrically-evoked responses trends towards being stronger in PMR; and (3) the selective silencing of SS interneurons might not impart an effect on spontaneous inhibitory postsynaptic events

Focal Augmentation of Somatostatin Interneuron Function and Subsequent Circuit Effects in Developmentally Malformed, Epileptogenic Cortex

Drug-resistant epilepsy (DRE) is a common clinical sequela of developmental cortical malformations such as polymicrogyria. Unfortunately, much remains unknown about the aberrant GABA-mediated circuit alterations that underlie DRE\u27s onset and persistence in this context. To address this knowledge gap, we utilized the transcranial freeze lesion model in optogenetic mice lines (Somatostatin (SST)-Cre or Parvalbumin (PV)-Cre x floxed channelrhodopsin-2) to dissect features of the SST, PV, and pyramidal neuron microcircuit that are potentially associated with DRE. Investigations took place within developmental microgyria’s known pathological substrate, the adjoined and epileptogenic paramicrogyral region (PMR). As well, microcircuit relationships within the previously unexplored range of normal-appearing cortex beyond PMR’s terminus were also interrogated. We previously demonstrated SST interneuron output enhancement onto postsynaptic layer V pyramidal neurons of PMR. Dissertation studies elaborated on this SST-interneuron mediated effect through the utilization of ex vivo slice electrophysiology in conjunction with selective optical activation of either SST or PV interneurons. An ostensible mechanism was identified in the form of a novel structural schematic for SST interneurons of PMR whereby they exhibit wider reaching, within-layer arborization of axons within this pathological substrate. Also, within PMR, SST interneuron output was not enhanced onto postsynaptic layer V PV interneurons, indicating targeting specificity of the SST to pyramidal neuron effect. Moving beyond PMR, past its terminus, SST interneuron output onto layer V pyramidal cells was found to be equivalent to controls, indicating effect focality. Finally, a novel disinhibitory relationship was demonstrated beyond PMR’s terminus, wherein PV interneurons exhibited output enhancement onto postsynaptic layer V SST interneurons. This indicates a putative in vivo mechanism for the PMR-focality of the SST to pyramidal neuron output enhancement scheme. These novel discoveries will provide the field with more context as to the role SST and PV interneurons potentially play in the emergence and/or modulation of drug-resistant epilepsy in and outside the terminus of PMR

Rubinstein-Taybi syndrome in diverse populations

Rubinstein-Taybi syndrome (RSTS) is an autosomal dominant disorder, caused by loss-of-function variants in CREBBP or EP300. Affected individuals present with distinctive craniofacial features, broad thumbs and/or halluces, and intellectual disability. RSTS phenotype has been well characterized in individuals of European descent but not in other populations. In this study, individuals from diverse populations with RSTS were assessed by clinical examination and facial analysis technology. Clinical data of 38 individuals from 14 different countries were analyzed. The median age was 7 years (age range: 7 months to 47 years), and 63% were females. The most common phenotypic features in all population groups included broad thumbs and/or halluces in 97%, convex nasal ridge in 94%, and arched eyebrows in 92%. Face images of 87 individuals with RSTS (age range: 2 months to 47 years) were collected for evaluation using facial analysis technology. We compared images from 82 individuals with RSTS against 82 age- and sex-matched controls and obtained an area under the receiver operating characteristic curve (AUC) of 0.99 (p < .001), demonstrating excellent discrimination efficacy. The discrimination was, however, poor in the African group (AUC: 0.79; p = .145). Individuals with EP300 variants were more effectively discriminated (AUC: 0.95) compared with those with CREBBP variants (AUC: 0.93). This study shows that clinical examination combined with facial analysis technology may enable earlier and improved diagnosis of RSTS in diverse populations