Faculty Bibliography

Studies have demonstrated non-myocytes, including fibroblasts, can electrically couple to myocytes in culture. However, evidence demonstrating current can passively spread across scar tissue in the intact heart remains elusive. We hypothesize electrotonic conduction occurs across non-myocyte gaps in the heart and is partly mediated by Connexin43 (Cx43). We investigated whether non-myocytes in ventricular scar tissue are electrically connected to surrounding myocardial tissue in wild type and fibroblast-specific protein-1 driven conditional Cx43 knock-out mice (Cx43fsp1KO). Electrical coupling between the scar and uninjured myocardium was demonstrated by injecting current into the myocardium and recording depolarization in the scar through optical mapping. Coupling was significantly reduced in Cx43fsp1KO hearts. Voltage signals were recorded using microelectrodes from control scars but no signals were obtained from Cx43fsp1KO hearts. Recordings showed significantly decreased amplitude, depolarized resting membrane potential, increased duration and reduced upstroke velocity compared to surrounding myocytes, suggesting that the non-excitable cells in the scar closely follow myocyte action potentials. These results were further validated by mathematical simulations. Optical mapping demonstrated that current delivered within the scar could induce activation of the surrounding myocardium. These data demonstrate non-myocytes in the scar are electrically coupled to myocytes, and coupling depends on Cx43 expression.

As information propagates along the ventral visual hierarchy, neuronal responses become both more specific for particular image features and more tolerant of image transformations that preserve those features. Here, we present evidence that neurons in area V2 are selective for local statistics that occur in natural visual textures, and tolerant of manipulations that preserve these statistics. Texture stimuli were generated by sampling from a statistical model, with parameters chosen to match the parameters of a set of visually distinct natural texture images. Stimuli generated with the same statistics are perceptually similar to each other despite differences, arising from the sampling process, in the precise spatial location of features. We assessed the accuracy with which these textures could be classified based on the responses of V1 and V2 neurons recorded individually in anesthetized macaque monkeys. We also assessed the accuracy with which particular samples could be identified, relative to other statistically matched samples. For populations of up to 100 cells, V1 neurons supported better performance in the sample identification task, whereas V2 neurons exhibited better performance in texture classification. Relative to V1, the responses of V2 show greater selectivity and tolerance for the representation of texture statistics.

Alzheimer's disease (AD) is characterized by a decrease in the enzymatic activity of the enzyme acetylcholinesterase (AChE). AChE is expressed as multiple splice variants, which may serve both cholinergic degradative functions and non-cholinergic functions unrelated with their capacity to hydrolyze acetylcholine. We have recently demonstrated that a prominent pool of enzymatically inactive AChE protein exists in the AD brain. In this study, we analyzed protein and transcript levels of individual AChE variants in human frontal cortex from AD patients by western blot analysis using specific anti-AChE antibodies and by quantitative real-time PCR (qRT-PCR). We found similar protein and mRNA levels of the major cholinergic "tailed"-variant (AChE-T) and the anchoring subunit, proline-rich membrane anchor (PRiMA-1) in frontal cortex obtained from AD patients and non-demented controls. Interestingly, we found an increase in the protein and transcript levels of the non-cholinergic "readthrough" AChE (AChE-R) variants in AD patients compared to controls. Similar increases were detected by western blot using an antibody raised against the specific N-terminal domain, exclusive of alternative N-extended variants of AChE (N-AChE). In accordance with a subset of AChE-R monomers that display amphiphilic properties that are upregulated in the AD brain, we demonstrate that the increase of N-AChE species is due, at least in part, to N-AChE-R variants. In conclusion, we demonstrate selective alterations in specific AChE variants in AD cortex, with no correlation in enzymatic activity. Therefore, differential expression of AChE variants in AD may reflect changes in the pathophysiological role of AChE, independent of cholinergic impairment or its role in degrading acetylcholine.

The mechanism of memory remains one of the great unsolved problems of biology. Grappling with the question more than a hundred years ago, the German zoologist Richard Semon formulated the concept of the engram, lasting connections in the brain that result from simultaneous "excitations", whose precise physical nature and consequences were out of reach of the biology of his day. Neuroscientists now have the knowledge and tools to tackle this question, however, and this Forum brings together leading contemporary views on the mechanisms of memory and what the engram means today.

The zebra finch brain features a set of clearly defined and hierarchically arranged motor nuclei that are selectively responsible for producing singing behavior. One of these regions, a critical forebrain structure called HVC, contains premotor neurons that are active at precise time points during song production. However, the neural representation of this behavior at a population level remains elusive. We used two-photon microscopy to monitor ensemble activity during singing, integrating across multiple trials by adopting a Bayesian inference approach to more precisely estimate burst timing. Additionally, we examined spiking and motor-related synaptic inputs using intracellular recordings during singing. With both experimental approaches, we find that premotor events do not occur preferentially at the onsets or offsets of song syllables or at specific subsyllabic motor landmarks. These results strongly support the notion that HVC projection neurons collectively exhibit a temporal sequence during singing that is uncoupled from ongoing movements.

Sleep exerts many effects on mammalian forebrain networks, including homeostatic effects on both synaptic strengths and firing rates. We used large-scale recordings to examine the activity of neurons in the frontal cortex of rats and first observed that the distribution of pyramidal cell firing rates was wide and strongly skewed toward high firing rates. Moreover, neurons from different parts of that distribution were differentially modulated by sleep substates. Periods of nonREM sleep reduced the activity of high firing rate neurons and tended to upregulate firing of slow-firing neurons. By contrast, the effect of REM was to reduce firing rates across the entire rate spectrum. Microarousals, interspersed within nonREM epochs, increased firing rates of slow-firing neurons. The net result of sleep was to homogenize the firing rate distribution. These findings are at variance with current homeostatic models and provide a novel view of sleep in adjusting network excitability.

Developmental ethanol exposure can lead to long-lasting cognitive impairment, hyperactivity, and emotional dysregulation among other problems. In healthy adults, sleep plays an important role in each of these behavioral manifestations. Here we explored circadian rhythms (activity, temperature) and slow-wave sleep in adult mice that had received a single day of ethanol exposure on postnatal day 7 and saline littermate controls. We tested for correlations between slow-wave activity and both contextual fear conditioning and hyperactivity. Developmental ethanol resulted in adult hyperactivity within the home cage compared to controls but did not significantly modify circadian cycles in activity or temperature. It also resulted in reduced and fragmented slow-wave sleep, including reduced slow-wave bout duration and increased slow-wave/fast-wave transitions over 24 hour periods. In the same animals, developmental ethanol exposure also resulted in impaired contextual fear conditioning memory. The impairment in memory was significantly correlated with slow-wave sleep fragmentation. Furthermore, ethanol treated animals did not display a post-training modification in slow-wave sleep which occurred in controls. In contrast to the memory impairment, sleep fragmentation was not correlated with the developmental ethanol-induced hyperactivity. Together these results suggest that disruption of slow-wave sleep and its plasticity are a secondary contributor to a subset of developmental ethanol exposure's long-lasting consequences.

Oxytocin promotes social interactions and recognition of conspecifics that rely on olfaction in most species. The circuit mechanisms through which oxytocin modifies olfactory processing are incompletely understood. Here, we observed that optogenetically induced oxytocin release enhanced olfactory exploration and same-sex recognition of adult rats. Consistent with oxytocin's function in the anterior olfactory cortex, particularly in social cue processing, region-selective receptor deletion impaired social recognition but left odor discrimination and recognition intact outside a social context. Oxytocin transiently increased the drive of the anterior olfactory cortex projecting to olfactory bulb interneurons. Cortical top-down recruitment of interneurons dynamically enhanced the inhibitory input to olfactory bulb projection neurons and increased the signal-to-noise of their output. In summary, oxytocin generates states for optimized information extraction in an early cortical top-down network that is required for social interactions with potential implications for sensory processing deficits in autism spectrum disorders.

Allosteric regulation promises to open up new therapeutic avenues by increasing drug specificity at G-protein-coupled receptors (GPCRs). However, drug discovery efforts are at present hampered by an inability to precisely control the allosteric site. Herein, we describe the design, synthesis, and testing of PhotoETP, a light-activated positive allosteric modulator of the glucagon-like peptide-1 receptor (GLP-1R), a class B GPCR involved in the maintenance of glucose homeostasis in humans. PhotoETP potentiates Ca(2+) , cAMP, and insulin responses to glucagon-like peptide-1 and its metabolites following illumination of cells with blue light. PhotoETP thus provides a blueprint for the production of small-molecule class B GPCR allosteric photoswitches, and may represent a useful tool for understanding positive cooperativity at the GLP-1R.