Gene-Environment Interaction in a Conditional NMDAR-Knockout Model of Schizophrenia

Interactions between genetic and environmental risk factors take center stage in the pathology of schizophrenia. We assessed if the stressor of reduced environmental enrichment applied in adulthood provokes deficits in the positive, negative or cognitive symptom domains of schizophrenia in a mouse line modeling NMDA-receptor (NMDAR) hypofunction in forebrain inhibitory interneurons (Grin1ΔPpp1r2). We find that Grin1ΔPpp1r2 mice, when group-housed in highly enriched cages, appear largely normal across a wide range of schizophrenia-related behavioral tests. However, they display various short-term memory deficits when exposed to minimal enrichment. This demonstrates that the interaction between risk genes causing NMDA-receptor hypofunction and environmental risk factors may negatively impact cognition later in life

Open-source, Python-based, hardware and software for controlling behavioural neuroscience experiments

Laboratory behavioural tasks are an essential research tool. As questions asked of behaviour and brain activity become more sophisticated, the ability to specify and run richly structured tasks becomes more important. An increasing focus on reproducibility also necessitates accurate communication of task logic to other researchers. To these ends, we developed pyControl, a system of open-source hardware and software for controlling behavioural experiments comprising a simple yet flexible Python-based syntax for specifying tasks as extended state machines, hardware modules for building behavioural setups, and a graphical user interface designed for efficiently running high-throughput experiments on many setups in parallel, all with extensive online documentation. These tools make it quicker, easier, and cheaper to implement rich behavioural tasks at scale. As important, pyControl facilitates communication and reproducibility of behavioural experiments through a highly readable task definition syntax and self-documenting features. Here, we outline the system’s design and rationale, present validation experiments characterising system performance, and demonstrate example applications in freely moving and head-fixed mouse behaviour

Optogenetic analysis of inhibitory circuits in the neocortex

Information processing in the brain involves circuits composed of different classes of neurons. Inhibitory interneurons are by far the most diverse subgroup in terms of physiology and morphology, and the principles that govern their connectivity are far from understood. Their excitatory counterparts, pyramidal and spiny stellate cells, have been found to be governed by a compartmentalized horizontal and vertical structure – forming layers and columns – as well as by a stereotypic or “canonical” pattern of connections between them. However, it has remained unclear whether similar, general organizing principles exist for inhibitory circuits. To map the sources of inhibitory inputs to neocortical pyramidal cells, a Cre-lox-based mouse knock-in line, that conditionally expresses the light-sensitive ion channel channelrhodopsin-2 in GABAergic neurons, was generated. Expression levels were sufficient to drive interneuron spiking at up to 40 Hz, but too low to activate synaptic terminals allowing perisomatic activation and thus mapping of local connections. I found, that inhibitory inputs to excitatory cells in all layers in primary motor (M1), somatosensory (S1), and visual cortex (V1) derive largely from the same layer and putative column. However, four translaminar inhibitory connections were found, which differ significantly both, between as well as within a cortical area. Most notably, (some) excitatory cells in layers 2/3, 4 and 5B of V1 receive prominent, putative feedback inhibition from their direct or indirect output layers. Furthermore, while a columnar structure is visible also in inhibitory circuits, their laminar organization is degenerate in an area-specific manner. Neocortical inhibitory microcircuits thus display significant variations, which potentially reflect the localization of function.</p

Optogenetic analysis of inhibitory circuits in the neocortex

&nbsp;This thesis is not currently available in ORA

Optogenetic mapping of neuronal connections and their plasticity

No abstract available

Sensory deprivation causes motif-specific changes in inhibitory connection strength.

<p>Voltage-clamp recordings at a holding potential of 0 mV from L2/3 pyramidal neurons in barrel-related columns representing intact (left, <i>n</i> = 23), trimmed (center left, <i>n</i> = 23), or previously deprived whiskers after regrowth for 1 mo (center right, <i>n</i> = 19) or 3 mo (right, <i>n</i> = 17). IPSCs were evoked by optical stimulation of interneurons in the indicated cortical layers; traces of all individual IPSCs (gray) were aligned to the time at which the rising IPSC reached half-maximal amplitude. Bold black traces indicate group averages. Colored columns represent the mean integrated current (charge transfer) per IPSC. Red columns mark significant differences associated with partial whisker regrowth (<i>p</i><0.05; ANOVA); dark yellow columns indicate groups whose means differ from the state of partial whisker regrowth (Bonferroni-corrected <i>t</i> test). Asterisks mark pairwise differences remaining after whisker regrowth for 3 mo (<i>p</i><0.05; ANOVA followed by Bonferroni-corrected <i>t</i> test). See also <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001798#pbio.1001798.s003" target="_blank">Figure S3</a> and <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001798#pbio.1001798.s004" target="_blank">Figure S4</a>.</p

Sensory deprivation causes motif-specific changes in inhibitory input numbers.

<p>Absolute number of locations in the indicated source layers (rows) giving rise to IPSCs in L2/3 pyramidal neurons in barrel-related columns representing intact (left, <i>n</i> = 23), trimmed (center left, <i>n</i> = 23), and previously deprived whiskers after regrowth for 1 mo (center right, <i>n</i> = 19) and 3 mo (right, <i>n</i> = 17). Colored columns represent group averages. Red columns mark significant differences associated with whisker trimming (<i>p</i><0.05; ANOVA); dark yellow columns indicate groups whose means differ from the whisker-trimmed state (Bonferroni-corrected <i>t</i> test). No significant differences exist between control and regrowth conditions (<i>p</i>>0.05; ANOVA).</p

Sensory deprivation causes motif-specific changes in laminar inhibitory connectivity.

<p>(A) Maps of inhibitory inputs to L2/3 pyramidal neurons in columns representing intact (left, <i>n</i> = 23), trimmed (center left, <i>n</i> = 23), or previously deprived whiskers after regrowth for 1 mo (center right, <i>n</i> = 19) or 3 mo (right, <i>n</i> = 17). The maps are scaled to the size of a standard barrel (yellow outline) and overlaid to depict the distribution of inhibitory input sources. The intensity of gray shading at each location indicates the cumulative inhibitory charge transfer. This normalized index measures the frequency with which IPSCs are elicited from corresponding locations in different slices, weighted by the average charge transfer per IPSC. (B) Normalized inhibitory charge flow from the indicated source layers (rows) to L2/3 pyramidal neurons in columns representing intact (left, <i>n</i> = 23), trimmed (center left, <i>n</i> = 23), or previously deprived whiskers after regrowth for 1 mo (center right, <i>n</i> = 19) or 3 mo (right, <i>n</i> = 17). Values are represented numerically (±1 SD) and in normalized gray scale. Red outlines mark significant differences associated with whisker trimming (<i>p</i><0.05; ANOVA); blue outlines indicate groups whose means differ from the whisker-trimmed state (Bonferroni-corrected <i>t</i> test). (C) Same display as (B), but illustrating absolute laminar inhibitory charge flow in pC (mean ± 1 SD). An additional significant difference exists in L1 between the 1-mo-regrowth condition (red asterisk) and columns representing intact and fully regrown whiskers (blue asterisks) (<i>p</i><0.05; Bonferroni-corrected <i>t</i> test).</p

Sensory deprivation causes motif-specific changes in inhibitory input numbers also in spared barrel-related columns.

<p>Absolute number of locations in the indicated source layers (rows) giving rise to IPSCs in L2/3 pyramidal neurons in barrel-related columns representing intact (left, <i>n</i> = 13, column C), spared (spared, <i>n</i> = 12, column C), or deprived whiskers (right, <i>n</i> = 23, columns A, B, D, and E; same data as in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001798#pbio-1001798-g006" target="_blank">Figure 6</a>, center left). Colored columns represent group averages. Red columns mark significant differences between the spared barrel-related column in deprived cortex and the comparison groups indicated in dark yellow (<i>p</i><0.05, <i>t</i> test).</p

Plasticity of inhibitory wiring motifs in a functional context.

<p>(A) L2/3 pyramidal cells in barrel cortex of mice with intact whiskers receive feed-forward (yellow), feedback (blue), and top-down inhibition (red). Interneurons providing these different forms of inhibition are located in different cortical layers, where they are driven, respectively, by thalamocortical afferents and cortical excitatory neurons (L4 and L2/3 interneurons, yellow); by intracortical or cortico-thalamo-cortical loops (L4 septal and L5B interneurons, blue); and by interareal excitatory connections terminating in L1 (red). (B) Whisker trimming leads to motif-specific changes in connection probabilities: existing inhibitory connections from L4 and L5B are eliminated, whereas new inhibitory connections from L1 are formed. (C) Partial whisker regrowth leads to overcompensation of deprivation-induced changes in connection probabilities and a large reduction in the strength of inhibitory connections from L1 and L2/3. (D) Full whisker regrowth restores connection probabilities to baseline. The strength of inhibitory connections from L1 and L2/3 recovers only partially.</p