Chemogenetic inhibition of prefrontal projection neurons constrains top-down control of attention in young but not aged rats.

The prefrontal cortex (PFC) governs top-down control of attention and is known to be vulnerable in aging. Cortical reorganization with increased PFC recruitment is suggested to account for functional compensation. Here, we hypothesized that reduced PFC output would exert differential effects on attentional capacities in young and aged rats, with the latter exhibiting a more robust decline in performance. A chemogenetic approach involving designer receptors exclusively activated by designer drugs was utilized to determine the impact of silencing PFC projection neurons in rats performing an operant attention task. Visual distractors were presented in all behavioral testing sessions to tax attentional resources. Under control conditions, aged rats exhibited impairments in discriminating signals with the shortest duration from non-signal events. Surprisingly, chemogenetic inhibition of PFC output neurons did not worsen performance amongst aged animals. Conversely, significant impairments in attentional capacities were observed in young subjects following such manipulation. Given the involvement of PFC-projecting basal forebrain cholinergic neurons in top-down regulation of attention, amperometric recordings were conducted to measure alterations in prefrontal cholinergic transmission in a separate cohort of young and aged rats. While PFC silencing resulted in a robust attenuation of tonic cholinergic signaling across age groups, the capacity to generate phasic cholinergic transients was impaired only amongst young animals. Collectively, our findings suggest a reduced efficiency of PFC-mediated top-down control of attention and cholinergic system in aging, and that activity of PFC output neurons does not reflect compensation in aged rats, at least in the attention domain.

Dynamic interplay of frontoparietal cholinergic innervation and cortical reorganization in the regulation of attentional capacities in aging.

Cortical remodeling is linked to age-related cognitive changes in humans; however, the mechanisms underlying cortical reorganization in aging remain unknown. Here we examined the consequences of mild cholinergic thinning of the prefrontal cortex (PFC) and parietal cortex (PC) on attention performance-associated changes in cortical activity in young and aged rats. Prefrontal manipulation produced attentional deficits in aged but not young rats regardless of cholinergic pruning. Stereological assessment of c-fos expression revealed age-related reductions in occipital activity and a corresponding increase in PC activity, but these patterns did not correlate with performance. PC cholinergic deafferentation produced opposite changes in PFC recruitment between young and aged rats. Cholinergic pruning reversed the effects of PFC/PC cholinergic manipulations on the activity of CaMKII- and GAD-positive neurons in aged rats. Our results indicate that cortical shifts depend on multiple factors including chronological age, cholinergic changes, and cortical insult, and that cortical reorganization is not necessarily compensatory. Moreover, the cholinergic system modulates excitation/inhibition homeostasis to improve the efficiency of reorganized cortical circuits and stabilize attentional performance.

Kinetic Characterization of ASXL1/2-Mediated Allosteric Regulation of the BAP1 Deubiquitinase.

BAP1 is an ubiquitin hydrolase whose deubiquitinase activity is mediated by polycomb group-like protein ASXL2. Cancer-related BAP1 mutations/deletions lead to loss-of-function by targeting the catalytic ubiquitin C-terminal hydrolase (UCH) or UCH37-like domain (ULD) domains of BAP1, and the latter disrupts binding to ASXL2, an obligate partner for BAP1 enzymatic activity. However, the biochemical and biophysical properties of domains involved in forming the enzymatically active complex are unknown. Here, we report the molecular dynamics, kinetics, and stoichiometry of these interactions. We demonstrate that interactions between BAP1 and ASXL2 are direct, specific, and stable to biochemical and biophysical manipulations as detected by isothermal titration calorimetry (ITC), GST association, and optical biosensor assays. Association of the ASXL2-AB box greatly stimulates BAP1 activity. A stable ternary complex is formed, comprised of the BAP1-UCH, BAP1-ULD, and ASXL2-AB domains. Stoichiometric analysis revealed that one molecule of the ULD domain directly interacts with one molecule of the AB box. Real-time kinetic analysis of the ULD/AB protein complex to the BAP1-UCH domain, based on surface plasmon resonance, indicated that formation of the ULD/AB complex with the UCH domain is a single-step event with fast association and slow dissociation rates. In vitro experiments validated in cells that the ASXL-AB box directly regulates BAP1 activity. IMPLICATIONS: Collectively, these data elucidate molecular interactions between specific protein domains regulating BAP1 deubiquitinase activity, thus establishing a foundation for small-molecule approaches to reactivate latent wild-type BAP1 catalytic activity in BAP1-mutant cancers.

Transcriptomic changes in the prefrontal cortex of rats as a function of age and cognitive engagement.

Although changes in cognitive functions including attention are well documented in aging, the neurobiological basis for such alterations is not fully understood. Increasing evidence points towards the contribution of genetic factors in age-related cognitive decline. However, genetic studies have remained inconsistent in characterizing specific genes that could predict functional decline in aging. Here we utilized next generation RNA sequencing (RNA-seq) to identify patterns of differentially expressed genes in the prefrontal cortex (PFC), a brain region implicated in attention, of young and aged animals that were either cognitively trained or had limited cognitive engagement. Consistent with previous investigations, aging alone was associated with increased expression of genes involved in multiple facets of innate and adaptive immune responses. On the contrary, the expression of immunity-related transcripts was reduced by cognitive engagement. In addition, transcripts across a wide range of cellular processes, including those associated with neuronal remodeling and plasticity, were upregulated by this behavioral manipulation. Surprisingly, aged subjects accounted for higher mean counts of upregulated transcripts and lower mean counts for downregulated transcripts as compared to the young subjects. Because aged rats exhibited lower attentional capacities, it is plausible that transcriptional changes associated with performance in these animals were reflective of compensatory changes that occurred to cope with the declining integrity of PFC functioning. Interestingly, the effects of both aging and cognitive engagement resulted in an upregulation of transcripts linked to extracellular exosomes, suggesting such extracellular vesicles may moderate a reciprocal gene by environment interaction in order to facilitate the reorganization of PFC circuitry and maintain functionality. Taken together, these findings provide novel insights into the capacities of both cognitive engagement as well as aging to alter gene expression in the PFC, and how the effects of such dynamic factors relate to variation in age-related cognitive abilities.

Clinical profile and management outcome of acute dacryocystitis: two decades of experience in a tertiary eye care center.

AIM: To report the demographic profile, clinical presentation, and management outcome of acute dacryocystitis. METHODS: Retrospective study of 347 eyes of 320 patients, who presented to the Ophthalmic Plastic Clinic of a tertiary eye care center over a period of 22 years from January 1990 to March 2012 with acute dacryocystitis, were reviewed for demographic profile, clinical presentation, and management outcome. The numbers of patients with lacrimal disorders during the same period were retrieved to assess the incidence of acute dacryocystitis. Successful anatomical outcome was defined as patency on irrigation and a successful functional outcome was defined as resolution of infection and epiphora. RESULTS: The mean age at presentation was 37 years. The female to male ratio was 2:1. There was no difference in the laterality between the right and the left eyes. Bilateral disease was noted in 8.4% (27/320) patients. 23% (80/347) eyes presented with lacrimal abscess while 2.8% (10/347) eyes had orbital cellulitis. Intensive medical care with hospital admission was needed in 4.4% (14/320) patients. The mean time to resolution of acute symptoms was 10 days. 5.6% (18/320) patients developed a fistula, among which 83% (15/18) were following a spontaneous rupture of the lacrimal abscess. Dacryocystorhinostomy was performed in 82.5% (264/320) patients with an anatomical success of 94.5% and a functional success of 93.5%. CONCLUSIONS: Acute dacryocystitis comprises 2.4% of all patients presenting with lacrimal system disorders. Fistula formation is a sequel more commonly seen with spontaneous rupture of a lacrimal abscess. The long-term outcomes in patients presenting with acute dacryocystitis are good with a surgical success rate of 94.3%.

The microbiological profile of lacrimal abscess: two decades of experience from a tertiary eye care center.

BACKGROUND: The aim of this study is to exclusively report the microbiological spectrum of lacrimal abscess and the antibiotic sensitivity patterns of the organisms. Retrospective interventional study on 112 eyes of 112 patients who presented to the ophthalmic plastic clinic of a tertiary eye care center over a period of 23 years from January 1990 to February 2013 with lacrimal abscess were reviewed for demographic and microbiological profile. The culture results, organisms isolated, and their antibiotic sensitivity were studied. RESULTS: The mean age at presentation was 37 years. The female to male ratio was 2:1. There was no significant difference in the laterality between the right and left eyes. Gram-positive organisms were the most commonly isolated accounting for 56.3% (63/112), and the commonest species isolated was Staphylococcus aureus in 25% (28/112) of the patients. Hemophilus influenzae was the commonest gram-negative isolate accounting for 30.2% of all the gram-negative isolates. Of the patients, 10.7% (12/112) showed no organisms on smear as well as sterile cultures. Gram-positive organisms were commonly sensitive to penicillins and vancomycin whereas gram-negative organisms were sensitive to quinolones and aminoglycosides. CONCLUSIONS: Gram-positive organisms are quite common as compared to gram-negative ones in cases of lacrimal abscess. The results of this study have significant bearing on the treatment of patients with lacrimal abscess.