Biology subjects

Nagarajan, R.

Publications and source records attributed to Nagarajan, R..

6 recordsLinked to original sources

bioRxiv2022

Genetic ablation of dentate hilar somatostatin-positive GABAergic interneurons is sufficient to induce cognitive impairment

Aging is often associated with a decline in cognitive function. A reduction in the number of somatostatin-positive (SOM+) interneurons in the dentate gyrus (DG) has been described in cognitively impaired but not in unimpaired aged rodents. However, it remains unclear whether the reduction in SOM+ interneurons in the DG hilus is causal for age-related cognitive dysfunction. We hypothesized that hilar SOM+ interneurons play an essential role in maintaining cognitive function and that a reduction in the number of hilar SOM+ interneurons might be sufficient to induce cognitive dysfunction. Hilar SOM+ interneurons were ablated by expressing a diphtheria toxin transgene specifically in these interneurons, which resulted in a reduction in the number of SOM+/GAD-67+ neurons and dendritic spine density in the DG. C-fos and Iba-1 immunostainings were increased in DG and CA3 but not in CA1. Behavioral testing revealed a reduced recognition index in the novel object recognition test, a reduction in the percentage of correct alternations in the Y maze tests, and increased latencies and path lengths in the learning and the reversal learning phase of the Morris water maze. Our results show that partial genetic ablation of SOM+ hilar interneurons is sufficient to increase activity in DG and CA3, as has been described to occur with aging and to induce an impairment of learning and memory functions. Thus, partial ablation of hilar SOM+ interneurons may be a significant contributing factor to age-related cognitive dysfunction. These mice may also be useful as a cellularly defined model of hippocampal aging.

neuroscience↗

bioRxiv2022

Chronic intermittent propofol attenuates surgery-induced neuroinflammation, apoptosis, and cognitive impairment in aged mice

Surgery may lead to long-lasting cognitive deficits that are referred to as perioperative neurocognitive disorder (NCD), particularly in elderly patients. Currently, no interventions are routinely employed in clinical practice to prevent perioperative NCD. Here we show that perioperative chronic intermittent administration of propofol to aged mice undergoing laparotomy under isoflurane anesthesia effectively blocks the surgery-induced increase in nitrosative stress, increased expression of proapoptotic proteins, microglial activation, and cognitive deficits. By contrast, in the absence of surgery and anesthesia, propofol had little effect on biochemical parameters and led to cognitive improvement only in a subset of behavioral paradigms. The actions of propofol were largely absent in mice lacking the GABAA receptor 5-subunit, indicating that they are mediated by 5-containing GABAA receptors. These results demonstrate that propofol - via 5-containing GABAA receptors that are redistributed to the cell surface membranes in a sustained manner - can attenuate surgery-induced neuroinflammation and postsurgical cognitive deficits.

neuroscience↗

bioRxiv2022

Dissecting the cellular basis of age-related cognitive dysfunction: Chronic chemogenetic inhibition of somatostatin-positive interneurons in the dentate gyrus hilus induces memory impairments

The cellular basis of age-related impairments of hippocampal function is not fully understood. In order to evaluate the role of somatostatin-positive (Sst+) interneurons in the dentate gyrus hilus in this process, we chemogenetically inhibited Sst+ interneurons in the dentate gyrus (DG) hilus. Chronic chemogenetic inhibition (CCI) of these neurons resulted in increased c-Fos staining in the DG hilus, a decrease in the percentage of Gad67- and of Sst-expressing interneurons in the DG, and increased microglial activation in DG, CA3, and CA1. Total dendritic length and spine density were reduced in DG and CA1, suggesting reduced dendritic complexity. Behaviorally, the recognition index in an object recognition task and the percentage of spontaneous alternations in the Y maze were decreased, while in both initial and reversal learning in the Morris water maze the latencies to find the hidden platform were increased, suggesting cognitive dysfunction. Our findings establish a causal role for a reduced function of Sst+ interneurons in the DG hilus for cognitive decline and suggest that this reduced function may contribute to age-related impairments of learning and memory. Furthermore, our CCI mice may represent a cellularly defined model of hippocampal aging. SIGNIFICANCE STATEMENTNeuronal circuits and cellular processes underlying age-related cognitive dysfunction are not well understood. We observed that chronic chemogenetic inhibition of a defined cell type, somatostatin-positive interneurons in the dentate gyrus hilus, which have previously been found to be associated with cognitive dysfunction in aged rodents, is necessary and sufficient to elicit changes in expression of interneuronal markers, an increase in the activity of dentate gyrus granule cells, increased microglial activation across the entire hippocampus and an impairment of learning and memory-related tasks. Thus, inhibition of somatostatin-positive interneurons in the dentate gyrus hilus replicates changes that are also seen with normal aging, representing a novel cellularly defined animal model of hippocampal aging.

neuroscience↗

bioRxiv2022

Control of contextual memory through interneuronal α5-GABAA receptors

{gamma}-aminobutyric acid type A receptors that incorporate 5 subunits (5-GABAARs) are highly enriched in the hippocampus and are strongly implicated in control of learning and memory. Receptors located on pyramidal neuron dendrites have long been considered responsible, but here we report that their selective knockout from either interneurons (5-i-KO) or pyramidal neurons (5-pyr-KO) interferes with the ability of the general anesthetic etomidate to suppress contextual conditioning. Using Ca2+ imaging of CA1 pyramidal neuron activity in freely exploring mice to assess hippocampal function directly, we found that etomidate blocked the development of place cells and spatial engrams in wild type (WT) and 5-pyr-KO mice, but not in 5-i-KO mice. In addition, 5-i-KO mice developed weaker spatial engrams than WT mice under control conditions. These findings show that interneuronal 5-GABAARs serve a physiological role in promoting spatial learning, and that they mediate the suppression of hippocampus-dependent memory by etomidate.

neuroscience↗

bioRxiv2021

Mapping QTLs for phenotypic and morpho-physiological traits related to grain yield under late sown conditions in wheat (Triticum aestivum L.)

The elevating temperature makes heat stress one of the major issues for wheat production globally. To elucidate genetic basis and map heat tolerance traits, a set of 166 doubled haploid lines (DHLs) derived from the cross between PBW3438/IC252874 was used. The population was evaluated under Normal sown (NS) and late sown (LS) conditions, by exposing to heat stress during rabi season. The canopy temperature (CT) showed positive correlations with grain yield, whereas Soil plant analysis development (SPAD) was not significantly correlated and associated with GY in both the normal and late sown conditions. Composite interval mapping (CIM) identified total 12 Quantitative trait loci (QTLs) viz., 2 (Normal sown), 10 (late sown) mapped on linkage groups 1A, 1D, 2B, 2D, 3B, 4D, 5B and 6D, during both the crop seasons 2017-18 and 2018-19. Combining the results of these QTLs revealed a major stable QTL for grain yield (GY) on chromosome 3B with 11.84% to 21.24% explaining phenotypic variance under both sowing conditions. QTL for CT and SPAD was detected on chromosome 1A while QTL for GY on chromosome 3B and 5B. The identified QTLs in the genomic regions could be targeted for genetic improvement and marker assisted selection for heat tolerance in wheat. The tools like SPAD and CT could be exploited to screen the large number of breeding lines.

plant biology↗

bioRxiv2021

Development of the Wheat Practical Haplotype Graph Database as a Resource for Genotyping Data Storage and Genotype Imputation

To improve the efficiency of high-density genotype data storage and imputation in bread wheat (Triticum aestivum L.), we applied the Practical Haplotype Graph (PHG) tool. The wheat PHG database was built using whole-exome capture sequencing data from a diverse set of 65 wheat accessions. Population haplotypes were inferred for the reference genome intervals defined by the boundaries of the high-quality gene models. Missing genotypes in the inference panels, composed of wheat cultivars or recombinant inbred lines genotyped by exome capture, genotyping-by-sequencing (GBS), or whole-genome skim-seq sequencing approaches, were imputed using the wheat PHG database. Though imputation accuracy varied depending on the method of sequencing and coverage depth, we found 93% imputation accuracy with 0.01x sequence coverage, which was only slightly lower than the accuracy obtained using the 0.5x sequence coverage (96.9%). Compared to Beagle, on average, PHG imputation was ~4% (p-value = 0.00027) more accurate, and showed 27% higher accuracy at imputing a rare haplotype introgressed from a wild relative into wheat. The reduced accuracy of imputation with GBS data (90.4%) is likely associated with the small overlap between GBS markers and the exome capture dataset, which was used for constructing PHG. The highest imputation accuracy was obtained with exome capture for the wheat D genome, which also showed the highest levels of linkage disequlibrium and proportion of identity-by-descent regions among accessions in our reference panel. We demonstrate that genetic mapping based on genotypes imputed using PHG identifies SNPs with a broader range of effect sizes that together explain a higher proportion of genetic variance for heading date and meiotic crossover rate compared to previous studies.

genomics↗