NI Neurofiziologijos laboratorija (11.06)

Author: Jonathan Kozal. Thesis: Optogenetic analysis of ON and OFF response in the rodent visual cortex (V1): Effects on Receptive field size and signal-to-noise ratio. The aim is to investigate whether for OFF responses optogenetic CamKll-expressing neuron stimulation can improve the accuracy of pinpointing the location of visual stimulus and reduce noise interference in area V1 in rats. Additionally, to examine whether these effects correlate between ON and OFF responses for single neurons. The objectives: 1. To determine the RF area change for OFF responses during pyramidal neuron stimulation. 2. To determine the SNR change for OFF responses during pyramidal neuron stimulation. 3. To compare the RF area change for ON and OFF responses. 4. To compare SNR changes for ON and OFF responses Methods: Wistar rats were anesthetized by peritoneal injections of urethane, then they were placed in a stereotaxic frame. The recordings were done 4-6 weeks following an injection in the visual cortex area of a virus containing channelrhodopsin (ChR2) under a short CamKII promoter. ChR2 reacts to blue 465nm light presentation by the opening of ion channels allowing for depolarization and activation of the neuron. A stereotaxic frame was used to fix the body of the rodent to accurately place the tetrode in the correct head location. An optic fiber for a 465nm blue LED stimulation was placed in the viral injected area (within deep cortical layers of area V1). A tetrode was inserted into area V1 to obtain real-time recordings of APs produced by the cells within area V1. Bright spots were presented on a dark grey background for visual stimulation. Initially, a single neuron RF area was determined during visual stimulation and then the RF area was evaluated again during optic fiber induced stimulation. Further analysis of recorded data performed by employing Igor pro, Matlab, KlustKwik software packages. Results: The RF area for OFF responses was reduced during optogenetic stimulation of pyramidal neurons, The area was 65.2% of control during stimulation (two-tail p value of 0.0063, Wilcoxon signed-rank test). SNR of OFF responses during stimulation of pyramidal neurons was 228% of control (two-tail p value of 2.67029e-005, Wilcoxon signed-rank test). No correlation was found for the RF area size change between ON and OFF responses during pyramidal neuron stimulation (Spearman R = -0.0769992, p >0.1), however, the extent of stimulation effect on RF area was similar: a median value was 79% for ON and 75% for OFF responses of the control RF area. Both ON and OFF responses responded by increasing SNR (medians- ON 250%, OFF 228%) Conclusions: LED light induced activation of pyramidal cells reduced the RF area of the OFF responses, which improved the precision of the visual object location detection. The stimulation increased SNR for OFF responses as well, improving information transmission quality by filtering out noise. Pyramidal cell stimulation resulted in similar reductions in RF area for ON and OFF responses, but these changes did not correlate for single neurons, suggesting that ON and OFF responses are independent in area V1. SNR improvements were similar for ON and OFF responses, demonstrating an overall improvement in signal clarity.

ABSTRACT Lena Green. Optogenetic Investigation of the Neuronal Population’s Effects on Visual lnformation Processing in the Rodent Primary Visual Cortex (Area V 1) The aim: to investigate whether visual information processing is improved in the primary visual cortex area V1 during local parvalbumin and CamKll-expressing neuron stimulation. The Objectives of the study. 1. To determine if the receptive field (RF) area is reduced in the area V1 Pyramidal Neurons during parvalbumin (PV) and CamKll neuron stimulation. 2. To determine if the RF area is reduced in the area V1 Interneurons during PV and CamKll neuron stimulation. 3.To determine if the background noise is reduced in the area V1 Pyramidal neurons during PV and CamKll neuron stimulation. 4. To determine if the background noise is reduced in the area V1 Interneurons during PV and CamKll neuron stimulation. Methods. Wistar rats were urethane anaesthetised and placed in a stereotactic frame; craniotomy with intact dura was made to reach the V1 area. A tetrode was lowered perpendicular to the superficial cortical layer. Visual stimuli were given as bright round spots on a dark screen; extracellular recordings were used to record action potentials. The RF area was measured as a visual field area in which stimulus presentation induced a significant increase in the unit firing rate. The responses modulated by the 480 nm laser light were measured after the injection of the PV_ChR134 virus and CamKIIa_ChR134 virus, that led to expression photosensitive ChR134 channels in PV interneurons and pyramidal (CaMKII+) neurons respectively. Results. The RF area was reduced in pyramidal neurons during both PV and pyramidal neuron stimulation. The background noise was reduced in pyramidal neurons during both PV and pyramidal neuron stimulation. In interneurons only RF area was reduced during both PV and pyramidal neuron stimulation. Conclusions. PV neuron activation, also via pyramidal neuron stimulation, can increase visual input reliability in V1 area by reducing background noise, improving signal-to-noise ratio, and better detection of visual stimulus location via reduced RF area. PV interneurons are fundamental for reliable visual information processing and an impairment of PV interneuron function in brain disorders should inevitably lead to deterioration of some aspects of vision. That can be used for diagnostics of such diseases

Author: Alend Mulla Ismail Title: Superior Colliculus and its link to Cervical Dystonia Aim: To better understand the function of the superior colliculus (SC) neurons located in deep layers (DLSC neurons) and to review papers suggesting that a disruption of basic processes in the DLSC can lead to the emergence of Cervical Dystonia (CD) symptoms. Objectives: 1. Investigate CD symptoms. 2. Investigate pathophysiological processes pertaining to CD. 3. Investigate processes within the SC that may lead to the emergence of CD symptoms. Methods and Materials: All papers reviewed in this thesis were found on PubMed and Google Scholar. All reviewed literature was written in English.
Results: This paper is a review of 20 articles, 4 of which include hypotheses that strongly align to the question of my thesis, these papers include both experiments and literature analyses. Out of these 20 articles, 2 described pharmacological disinhibition of DLSC neurons and the neurons of substantia nigra pars reticulata (microinfusions into the brain areas of interest of a GABA A receptor antagonist or an agonist, bicuculline or muscimol) in order to elicit conditions similar to those that researchers believe to cause the emergence of CD. The results of both papers support the notion that the reduced inhibitory activity in the SC neural circuits mediates the manifestation of symptoms that may be categorized as CD. Another important article was a systematic literature review on the same topic that attributed the cause of the excessive burst firing of premotor neurons in the SC to disinhibition of projections coming from the superficial layers of SC. The last article of major significance described an experiment that measured Temporal Discrimination Threshold (TDT) values in CD patients and their unaffected relatives. The obtained results strongly supported previous ideas that an abnormal TDT highly correlated with the presence of CD symptoms and was the feature of the disrupted processes within the SC itself. Conclusions: Recent research on the topic has demonstrated that the SC is indeed the most likely structure responsible for the CD symptoms since the disruption of intrinsic SC processes may cause these symptoms. However, the root cause of CD is likely to be found in the upstream neural circuits of the basal ganglia.