A longitudinal study of COVID-19 preventive behavior fatigue in Hong Kong: a city with previous pandemic experience.

BACKGROUND: In addition to high vaccination levels, COVID-19 control requires uptake and continued adherence to personal hygiene and social distancing behaviors. It is unclear whether residents of a city with successive experience in worldwide pandemics such as SARS, would quickly adopt and maintain preventive behaviors. METHODS: A population-based, longitudinal telephone survey was conducted between in first local wave of the COVID-19 pandemic (April 2020) and third local wave (December 2020) (n = 403). The study examined factors associated with personal hygiene and social distancing behavior fatigue, as measured by reduced adherence. RESULTS: Over 9 months, face mask use increased (96.5-100%, p < 0.001). Although habitual hand hygiene remained unchanged (92.0%), blue collar workers and non-working individuals showed higher risk of hand hygiene fatigue. There was a decline (p < 0.05) in avoidance of social gatherings (81.1 to 70.7%), avoidance of public places (52.9-27.5%) and avoidance of international travel (81.9-77.4%) even with rising caseloads. Lowered perception of COVID-19 disease severity was associated with decreased avoidance of social gatherings and public places while lower education was associated with decline in avoidance of social gatherings. CONCLUSION: Even in regions with past pandemic experience, maintaining social distancing behaviors during a protracted pandemic remains a major public health challenge.

Estimation of Vaccine Effectiveness of CoronaVac and BNT162b2 Against Severe Outcomes Over Time Among Patients With SARS-CoV-2 Omicron.

Importance: Few studies have evaluated the waning of vaccine effectiveness against severe outcomes caused by SARS-CoV-2 Omicron infection. Hong Kong is providing inactivated and mRNA vaccines, but the population had limited protection from natural infections before the Omicron variant emerged. Objective: To examine the change in vaccine effectiveness against hospitalization and mortality due to the Omicron variant over time. Design, Setting, and Participants: This case-control study included adults with SARS-CoV-2 Omicron variant infection who died or were hospitalized in Hong Kong from January 1 to June 5, 2022 (ie, case participants), and adults with SARS-CoV-2 Omicron, sampled from the public health registry during the study period (ie, control participants), who were matched to case participants by propensity score. Exposures: Vaccination status of the individuals. Main Outcomes and Measures: Estimated vaccine effectiveness against death, death or hospitalization, and death among hospitalized patients. Vaccine effectiveness was calculated as 1 - adjusted odds ratio obtained by conditional logistic regression adjusted with covariates for each period following vaccination. Results: There were 32 823 case participants (25 546 [77.8%] ≥65 years; 16 930 [47.4%] female) and 131 328 control participants (100 041 [76.2%] ≥65 years; 66 625 [46.6%] female) in the sample analyzed for the death or hospitalization outcome. Vaccine effectiveness against death or hospitalization was maintained for at least 6 months after the second dose of both CoronaVac (74.0%; 95% CI, 71.8%-75.8%) and BNT162b2 (77.4%; 95% CI, 75.5%-79.0%) vaccines. Vaccine effectiveness against death in those aged 18 to 49 years was 86.4% (95% CI, 85.8%-87.0%) and 92.9% (95% CI, 92.6%-93.2%) for those receiving 2 doses of CoronaVac and BNT162b2, respectively, while for patients aged 80 years or older, it dropped to 61.4% (95% CI, 59.8%-63.2%) and 52.7% (95% CI, 50.2%-55.6%) for CoronaVac and BNT162b2, respectively. Nevertheless, overall vaccine effectiveness against death at 4 to 6 months after the third dose was greater than 90% for CoronaVac, BNT162b2, and the mixed vaccine schedule (eg, mixed vaccines: vaccine effectiveness, 92.2%; 95% CI, 89.2%-95.1%). Conclusions and Relevance: While vaccines were generally estimated to be effective against severe outcomes caused by SARS-CoV-2 Omicron infection, this analysis found that protection in older patients was more likely to wane 6 months after the second dose. Hence, a booster dose is recommended for older patients to restore immunity. This is especially critical in a setting like Hong Kong, where third-dose coverage is still insufficient among older residents.

The Effect of Social Isolation on Sarcopenia: A Longitudinal Study among the Middle-Aged and Older Population in China.

INTRODUCTION: Although social isolation is associated with premature death and somatic and mental diseases, evidence of its long-term effect on sarcopenia is scarce. This study aimed to examine the longitudinal association between social isolation and possible sarcopenia. METHODS: We extracted baseline and 4-year follow-up data from the China Health and Retirement Longitudinal Study and included participants aged 45 years or above. Social isolation was measured by factors including living alone, marital status, frequency of contact with adult children and friends, and participation in social activity. The change in social isolation from baseline to follow-up was classified into stable, progressive, and regressive groups. Possible sarcopenia was detected using the handgrip strength and five-time chair-stand test. Using mixed-effects logistic regression, we studied the effect of baseline isolation and the change in isolation status on possible sarcopenia at a 4-year follow-up. RESULTS: A total of 5,289 participants aged 45-90 years and without possible sarcopenia at baseline were included. After 4 years, possible sarcopenia was detected in 21.7% (1,146/5,289) of the participants. Compared with the low social isolation group, the middle (OR = 1.53, 95% confidence interval [CI] = 1.16-2.04, p = 0.003) and high social isolation groups (OR = 1.65, 95% CI = 1.26-2.18, p < 0.001) were associated with a higher risk of possible sarcopenia. Being not married/cohabiting (OR = 1.58, 95% CI = 1.19-2.10, p = 0.002), lack of contact with children (OR = 1.86, 95% CI = 1.21-2.85, p = 0.004), and lack of social activities (OR = 1.26, 95% CI = 1.04-1.53, p = 0.019) were associated with an increased risk of possible sarcopenia. Compared with the stable social isolation group, the progressive group was associated with a greater risk of possible sarcopenia (OR = 1.51, 95% CI = 1.17-1.95, p = 0.001). CONCLUSIONS: Social isolation is associated with an increased risk of possible sarcopenia. Progressive social isolation further elevates the risk. The most vulnerable groups are middle-aged and older people who live alone, are not socially active, and lack contact with their children.

Prevalence and Factors Associated with Risky Sexual Behaviors Among Sexually Active Female Adolescents in Zambia.

Despite decades long commitment to women's reproductive health rights, sexually transmitted diseases and unintended pregnancies continue to be major public health concerns in sub-Saharan Africa. In order to provide an evidence base for future policy and services, this study aims to explore the prevalence and factors associated with risky sexual behaviors (RSB) among sexually active Zambian female adolescents using a nationally representative sample. Data on females, aged 15-19 (n = 3000), were obtained from the 2018 Zambia Demographic and Health Survey, an interviewer-administered, nationally representative survey that used multistage sampling. The study conducted multiple logistic regression to explore the correlates of RSB. Of the 3000 respondents, 49.7% (1490) reported ever having sexual intercourse of which 71.1% reported engaging in RSB. Among sexually active female adolescents, the following RSB percentage were reported: intercourse before age 16 (50.6%), nonuse of condoms at last intercourse (37.8%), engaging in transactional sex (6.2%), alcohol use at last intercourse (4.6%), and multiple sexual partners (1.9%). Educational attainment and household wealth showed strong inverse trends with RSB risk and there were notably large geographic differences in RSB within Zambia (22.1% in Lusaka region vs. 62.4% in Western province). The multiple logistic regression results revealed that those who were younger, unmarried, with less than secondary education, without access to Internet, and residents of Western Zambia were significantly more likely to have engaged in RSB (AOR: 1.74-7.69, p < 0.05). Given the negative health outcomes associated with RSB, Zambian adolescent health care programs may strategically target limited resources to the identified risk groups.

The differential impacts of early detection and accelerated antiretroviral therapy on the epidemiologic trend of sexually acquired HIV infection in Hong Kong.

OBJECTIVES: To assess impacts of early detection and prompt antiretroviral therapy (ART) on the latest epidemiologic situation to inform intervention strategy. METHODS: We analysed data from two clinical cohorts in Hong Kong where sexual transmission accounted for the majority of HIV infections. The two cohorts comprised patients newly diagnosed in 2007-2008 and 2016-2018 respectively. Secular trend and differences between men who have sex with men (MSM) and heterosexual patients were examined. Predictors of late presentation (defined as CD4 ≤350 or AIDS-defining illness within 3 months of diagnosis) and prolonged interval between diagnosis and ART initiation were assessed by multivariable regressions. RESULTS: There were 1,136 newly diagnosed HIV patients with 644 in the first and 492 in the second cohort, a majority (91.7%) presented with sexually acquired infection. There were less MSM in the first than the second cohort (50.3%% vs 87.8%, χ2 = 117.05, p<0.001). The mean (SD) number of days between diagnosis and ART initiation decreased from 514.3 (516.1) to 61.8 (94.2) days across the two cohorts. Younger age, non-Chinese, outpatient-based service and lower CD4 count were predictors of faster ART initiation in the first but not in the second cohort. Interval between diagnosis and ART initiation became highly uniform among groups in the second cohort. Nearly 60% were classified as late presenters in both cohorts. Heterosexuals (aOR 1.58, 95% CI 1.13-2.19) had a higher risk of late presentation. CONCLUSIONS: There was remarkable improvement in acceleration of ART initiation. Clinical implementation of accelerated ART recommendations has been effective for both MSM and heterosexuals. Late presentation was more marked among heterosexuals and remained a problem. The continued phenomenon of late presentation could offset the epidemiologic gains from accelerated ART initiation.

Global Burden, Regional Differences, Trends, and Health Consequences of Medication Nonadherence for Hypertension During 2010 to 2020: A Meta-Analysis Involving 27 Million Patients.

Background Nonadherence to antihypertensive medications is the leading cause of poor blood pressure control and thereby cardiovascular diseases and mortality worldwide. Methods and Results We investigated the global epidemiology, regional differences, and trend of antihypertensive medication nonadherence via a systematic review and meta-analyses of data from 2010 to 2020. Multiple medical databases and clinicaltrials.gov were searched for articles. Observational studies reporting the proportion of patients with anti-hypertensive medication nonadherence were included. The proportion of nonadherence, publication year, year of first recruitment, country, and health outcomes attributable to antihypertensive medication nonadherence were extracted. Two reviewers screened abstracts and full texts, classified countries according to levels of income and locations, and extracted data. The Joanna Briggs Institute prevalence critical appraisal tool was used to rate the included studies. Prevalence meta-analyses were conducted using a fixed-effects model, and trends in prevalence were analyzed using meta-regression. The certainty of evidence concerning the effect of health consequences of nonadherence was rated according to Grading of Recommendations, Assessment, Development and Evaluations. A total of 161 studies were included. Subject to different detection methods, the global prevalence of anti-hypertensive medication nonadherence was 27% to 40%. Nonadherence was more prevalent in low- to middle-income countries than in high-income countries, and in non-Western countries than in Western countries. No significant trend in prevalence was detected between 2010 and 2020. Patients with antihypertensive medication nonadherence had suboptimal blood pressure control, complications from hypertension, all-cause hospitalization, and all-cause mortality. Conclusions While high prevalence of anti-hypertensive medication nonadherence was detected worldwide, higher prevalence was detected in low- to middle-income and non-Western countries. Interventions are urgently required, especially in these regions. Current evidence is limited by high heterogeneity. Registration URL: www.crd.york.ac.uk/prospero/; Unique identifier: CRD42021259860.

Vaccine Resistance and Hesitancy among Older Adults Who Live Alone or Only with an Older Partner in Community in the Early Stage of the Fifth Wave of COVID-19 in Hong Kong.

Vaccination is an effective way in providing protection against COVID-19 infection and severe outcomes. However, vaccine resistance and hesitancy are a great concern among vulnerable populations including older adults who live alone or only with an older partner. This study examined their vaccination status and reasons and associated factors of vaccine resistance and hesitancy. A cross-sectional study was conducted among older adults living alone or only with an older partner in communities in Hong Kong. Participants were interviewed between October 2021 and February 2022. Logistic regression analyses were employed to examine factors associated with vaccine resistance and hesitancy. Of the 2109 included participants, the mean age was 79.3 years (SD 7.6), 1460 (69.2%) were female, 1334 (63.3%) lived alone, and 1621 (76.9%) were receiving social security support. The vaccine uptake, non-uptake (i.e., resistance), and hesitancy rates were 50.1%, 34.4%, and 15.5%, respectively. The top four reasons for vaccine resistance and hesitancy were "Not feeling in good health" (27%), "Worry about vaccine side effects" (18%), "Feeling no need" (10%), and "Lack of recommendation from doctors" (9%). Vaccine resistance and hesitancy was significantly associated with older age, living alone, more chronic conditions, fewer types of social media use, and lower self-rated health status. Similar associations can be observed in their separate analysis for vaccine resistance and vaccine hesitancy, and ever hospital admission over the past 6 months was additionally related to vaccine hesitancy. Older people who live alone or only with an older partner had a low vaccination rate. Poor health or worry about vaccine side effects were the most common reasons for their vaccine resistance and hesitancy. Actions are greatly needed to improve the uptake rate among this vulnerable population, especially those who were older, have poorer health, and use less social media.

Handgrip strength but not SARC-F score predicts cognitive impairment in older adults with multimorbidity in primary care: a cohort study.

BACKGROUND: Assessing motor function is a simple way to track cognitive impairment. We analysed the associations between cognitive and motor function and assessed the predictive value of two motor function measuring tools for cognitive impairment in older adults with multimorbidity in primary care settings. METHODS: We conducted a prospective cohort study with a 1 year follow-up. Patients aged ≥60 years with ≥2 morbidities were recruited from four primary care clinics. Motor function was assessed using handgrip strength and a sarcopenia screening scale (SARC-F). Cognitive function was measured using the Hong Kong Montreal Cognitive Assessment (HK-MoCA). We defined cognitive impairment as an HK-MoCA score < 22. The associations between cognitive and motor functions were examined from a bidirectional perspective. RESULTS: We included 477 participants (mean age 69.4, 68.6% female) with a mean (SD) HK-MoCA score of 25.5 (3.38), SARC-F score of 1.1 (1.36), and handgrip strength of 21.2 (6.99) kg at baseline. Multivariable linear regression models showed bidirectional cross-sectional associations of the HK-MoCA score and cognitive impairment with SARC-F score and handgrip strength at baseline and 1 year. Cox regression revealed a longitudinal association between baseline handgrip strength and cognitive impairment at 1 year (hazard ratio: 0.48, 95% CI 0.33-0.69) but no longitudinal association between SARC-F and cognitive impairment. Variation in the SARC-F score increased with decreasing HK-MoCA score (Brown-Forsythe test F statistic = 17.9, p < 0.001), while variability in the handgrip strength remained small (modified signed-likelihood ratio test, p < 0.001). CONCLUSIONS: Primary healthcare providers may use handgrip strength to track cognitive function decline in older adults with multimorbidity. However, the SARC-F scale may not have the same predictive value. Further research is needed to evaluate the performance and variability of the SARC-F score in individuals with poor cognitive function.

Controlled-release oral melatonin supplementation for hypertension and nocturnal hypertension: A systematic review and meta-analysis.

Oral melatonin is a potential alternative treatment for hypertension and nocturnal hypertension. However, high-quality and relevant meta-analyses are lacking. This meta-analysis aimed to investigate whether oral melatonin supplementation reduces daytime/asleep blood pressure and cardiovascular risk, improves sleep quality, and is well-tolerated compared with placebo. Relevant articles were searched in multiple databases, including MEDLINE, EMBASE, CINAHL Complete, and the Cochrane Library, from their inception to June 2021. The included studies were randomized controlled trials recruiting patients with hypertension, using oral melatonin as the sole intervention, and investigating its effect on blood pressure. The mean out-of-office (including 24-h, daytime, and asleep) systolic and diastolic blood pressures, sleep quality, and side effects were compared between the melatonin and placebo arms using pairwise random-effect meta-analyses. A risk of bias assessment was performed using the Cochrane risk-of-bias tool. Four studies were included in the analysis and only one study was considered to have a low risk of bias. No study reported on cardiovascular risk or outcomes. Only controlled-release melatonin (not an immediate-release preparation) reduced asleep systolic blood pressure by 3.57 mm Hg (95% confidence interval: -7.88 to .73; I2  = 0%). It also reduced asleep and awake diastolic blood pressure, but these differences were not statistically significant. Melatonin improves sleep efficacy and total sleep time and is safe and well-tolerated. Due to the limited number of high-quality trials, the quality of evidence was low to very low. Therefore, adequately powered randomized controlled trials on melatonin are warranted.

Poor health literacy associated with stronger perceived barriers to breast cancer screening and overestimated breast cancer risk.

Background: Low health literacy (HL) is negatively associated with mammography screening uptake. However, evidence of the links between poor HL and low mammography screening participation is scarce. Methods: We conducted a cross-sectional questionnaire survey among participants of a cancer screening program. We measured HL using a validated Chinese instrument. We assessed breast cancer screening-related beliefs using the Health Belief Model and the accuracy of risk perception. We used multivariable regression models to estimate the relationship between HL and the outcomes. Results: A total of 821 females were included. 264 (32.2%) had excellent or sufficient, 353 (43.0%) had problematic, and 204 (24.8%) had inadequate health literacy (IHL). Women with IHL were more likely to agree that high price (ß = -0.211, 95% CI -0.354 to -0.069), lack of time (ß = -0.219, 95% CI -0.351 to -0.088), inconvenient service time (ß = -0.291, 95% CI -0.421 to -0.160), long waiting time (ß = -0.305, 95% CI -0.447 to -0.164), fear of positive results (ß = -0.200, 95% CI -0.342 to -0.058), embarrassment (ß = -0.225, 95% CI -0.364 to -0.086), fear of pain (ß = -0.154, 95% CI -0.298 to -0.010), fear of radiation (ß = -0.177, 95% CI -0.298 to -0.056), lack of knowledge on service location (ß = -0.475, 95% CI -0.615 to -0.335), and lack of knowledge on mammography (ß = -0.360, 95% CI -0.492 to -0.228) were barriers. They were also less likely to have an accurate breast cancer risk perception (aOR 0.572, 95% CI 0.341 to 0.956). Conclusion: Women with lower HL could have stronger perceived barriers to BC screening and an over-estimation of their breast cancer risk. Tackling emotional and knowledge barriers, financial and logistical assistance, and guidance on risk perception are needed to increase their breast cancer screening uptake.

Recommending COVID-19 Vaccines to Patients: Practice and Concerns of Frontline Family Doctors.

Background: Recommendation from doctors is a well-recognized motivator toward vaccine uptake. Family doctors are in the prime position to advise the public on COVID-19 vaccination. We studied the practice and concerns of frontline family doctors concerning COVID-19 vaccination recommendations to patients. Methods: We conducted a cross-sectional online survey of all family doctors in the Hong Kong College of Family Physicians between June and July 2021. Their practice of making COVID-19 recommendation to patients was assessed. Based on the Health Belief Model, factors associated with doctors' recommendation practices were explored and examined. Multivariate logistic regression models were used to investigate the factors, including COVID-19 vaccine attributes, associated with doctors' practices in making recommendations. Their own vaccination status and psychological antecedents to vaccine hesitancy were measured. Results: A total of 312 family doctors responded (a 17.6% response rate). The proportion of doctors who had received COVID-19 vaccines was 90.1%. The proportion of doctors who would recommend all patients without contraindications for the vaccination was 64.4%. The proportion of doctors who would proactively discuss COVID-19 vaccines with patients was 52.9%. Multivariate logistic regression analysis showed that doctors' own COVID-19 vaccination status was the strongest predictor of family doctors making a recommendation to patients (aOR 12.23 95% CI 3.45-43.33). Longer duration of practice, willingness to initiate the relevant discussion with patients and less worry about vaccine side effects on chronic illness patients were the other factors associated with making a COVID-19 vaccination recommendation. Conclusions: Family doctors should be encouraged to get vaccinated themselves and initiate discussions with patients about COVID-19 vaccines. Vaccine safety data on patients with chronic illness, training and guidelines for junior doctors may facilitate the COVID-19 vaccination recommendation practices of family doctors.

Joint effect between bisphenol A and alcohol consumption on benign prostatic hyperplasia: A case-control study in Hong Kong Chinese males.

BACKGROUND: Whether bisphenol A (BPA) exposure is a contributing factor to benign prostatic hyperplasia (BPH) remains unclear. This study evaluated the association between chronic BPA exposure and BPH risk, and explored whether this association was modified by alcohol drinking. METHODS: This study included a total of 650 BPH cases and 650 controls recruited from the same hospital in Hong Kong during 2011-2016. Chronic BPA exposure level was estimated by a validated cumulative BPA exposure index (CBPAI). We performed unconditional logistic regression model to examine the association of BPH risk with potential sources of BPA exposure via oral intake and CBPAI. We further tested the interactions between CBPAI and alcohol consumption habits on BPH risk. RESULTS: A positive exposure-response relationship was observed between CBPAI and BPH risk. Frequent BPA exposure via oral intake of foods heated in a plastic box/bag (odds ratio [OR] = 3.52, 95% confidence interval [CI]: 1.51-8.22), cooling water in a plastic bottle (OR = 2.65, 95% CI: 1.33-5.27), or using a plastic cup to contain hot water (OR = 4.14, 95% CI: 1.02-16.89), was significantly associated with increased BPH risk. Compared with nonalcohol drinkers, alcohol drinkers was insignificantly associated with BPH risk (OR = 1.10, 95% CI: 0.77-1.57), but it demonstrated a more remarkable positive gradient between CBPAI exposure and BPH risk among alcohol drinkers, indicating an additive interaction between CBPAI and alcohol on BPH risk (synergy index = 4.24, 95% CI: 1.21-14.94). CONCLUSIONS: Chronic oral BPA exposure increased BPH risk with a positive exposure-response relationship among Hong Kong Chinese, and alcohol drinking amplified the effect of BPA on BPH. Hence, minimizations of containing food or water/beverage in plastic containers and drinking alcohol are recommended in the community to mitigate BPH risk. Future larger and designated studies are warranted.

Altered intensity coding in the salicylate-overdose animal model of tinnitus.

Tinnitus is one of the leading disorders of hearing with no effective cure as its pathophysiological mechanisms remain unclear. While the sensitivity to sound is well-known to be affected, exactly how intensity coding per se is altered remains unclear. To address this issue, we used a salicylate-overdose animal model of tinnitus to measure auditory cortical evoked potentials at various stimulus levels, and analyzed on single-trial basis the response strength and its variance for the computation of the lower bound of Fisher information. Based on Fisher information profiles, we compared the precision or efficiency of intensity coding before and after salicylate-treatment. We found that after salicylate treatment, intensity coding was unexpectedly improved, rather than impaired. Also, the improvement varied in a sound-dependent way. The observed changes are likely due to some central compensatory mechanisms that are activated during tinnitus to bring out the full capacity of intensity coding which is expressed only in part under normal conditions.

Frequency discrimination in rats exposed to noise as juveniles.

Sound exposure during the early postnatal period can significantly influence the function of the auditory system in rats during adulthood. In the present study, rat pups (strain Long-Evans) were exposed to broad-band noise at 125dB SPL for 8, 12 or 25min on postnatal day 14 and then at the age of 3-5months their frequency discrimination at 4 and 16kHz was assessed using a modified method of the prepulse inhibition of the acoustic startle reflex. In all groups of exposed rats, an altered frequency discrimination of the tonal stimuli was observed, in comparison with controls, at 70dB SPL. A worsening of frequency discrimination was observed even in animals exposed for 8min, the auditory thresholds of which were almost identical to that of control animals. The individual auditory thresholds did not correlate with frequency discrimination. The difference in frequency discrimination between the exposed and control animals disappeared at 85-90dB SPL. Our data suggests that brief noise exposure during the critical period of development results in the altered frequency discrimination at moderate sound intensities in adult rats, which may appear even in individuals with normal hearing thresholds.

Evaluation of microvasculature at the auditory midbrain--the benefits of sectioning at a tangential angle.

Vascular remodeling in the brain occurs as a plastic change following neural over-activity. The auditory midbrain (or inferior colliculus, IC) is an ideal place to study sound-induced vascular changes because it is the brain's most vascularized structure and it is tonotopically organized. However, its micro-vascular pattern remains poorly understood. Since the IC is a sphere-like structure, the histological assessment of vasculature could depend on the angle of sectioning. Here, we studied the effects of cutting the IC at different angles on microvascular assessment, specifically: micro-vascular density and the shape of microvascular lumen. Photomicrographs were taken from 5 µm toluidine blue-stained histological sections obtained at two angles of sectioning: (a) the conventional coronal sectioning, and (b) a novel "tangential" sectioning (tangential to the dorso-medial surface of the IC). Results showed that the tangential sections, in comparison with the coronal sections, yielded (a) a higher count of micro-vascular density and (b) a higher proportion of round-shaped micro-vascular lumens. This discrepancy in results between two cut angles is likely related to the spatial pattern of blood vessels supplying the IC. We propose that the tangential sectioning should be adopted as standard for the accurate study of microvasculature in the IC.

Prolonged sound exposure has different effects on increasing neuronal size in the auditory cortex and brainstem.

Tone at moderate levels presented to young rats at a stage (postnatal week-4) presumably that has passed the cortical critical period still can enlarge neurons in the auditory cortex. It remains unclear whether this delayed plastic change occurs only in the cortex, or reflects a change taking place in the auditory brainstem. Here we compared sound-exposure effects on neuronal size in the auditory cortex and the midbrain. Starting from postnatal day 22, young rats were exposed to a low-frequency tone (4 kHz at 65 dB SPL) for a period of 3 (postnatal day 22-25) or 7 (postnatal day 22-29) days before sacrifice. Neurons were analyzed morphometrically from 7 µm-thick histological sections. A marked increase in neuronal size (32%) was found at the cortex in the high-frequency region distant from the exposing tone. The increase in the midbrain was even larger (67%) and was found in both the low and high frequency regions. While cell enlargements were clear at day 29, only in the high frequency region of the cortex a slight enlargement was found at day 22, suggesting that the cortical and subcortical changes are synchronized, if not slightly preceded by the cortex. In contrast, no changes in neuronal size were found in the cochlear nucleus or the visual midbrain. Such differential effects of sound-exposure at the auditory centers across cortical and subcortical levels cannot be explained by a simple activity-driven change occurring earlier in the brainstem, and might involve function of other structures as for example the descending auditory system.

Modeling complex responses of FM-sensitive cells in the auditory midbrain using a committee machine.

Frequency modulation (FM) is an important building block of complex sounds that include speech signals. Exploring the neural mechanisms of FM coding with computer modeling could help understand how speech sounds are processed in the brain. Here, we modeled the single unit responses of auditory neurons recorded from the midbrain of anesthetized rats. These neurons displayed spectral temporal receptive fields (STRFs) that had multiple-trigger features, and were more complex than those with single-trigger features. Their responses have not been modeled satisfactorily with simple artificial neural networks, unlike neurons with simple-trigger features. To improve model performance, here we tested an approach with the committee machine. For a given neuron, the peri-stimulus time histogram (PSTH) was first generated in response to a repeated random FM tone, and peaks in the PSTH were segregated into groups based on the similarity of their pre-spike FM trigger features. Each group was then modeled using an artificial neural network with simple architecture, and, when necessary, by increasing the number of neurons in the hidden layer. After initial training, the artificial neural networks with their optimized weighting coefficients were pooled into a committee machine for training. Finally, the model performance was tested by prediction of the response of the same cell to a novel FM tone. The results showed improvement over simple artificial neural networks, supporting that trigger-feature-based modeling can be extended to cells with complex responses. This article is part of a Special Issue entitled Neural Coding 2012. This article is part of a Special Issue entitled Neural Coding 2012.

Deactivation of the inferior colliculus by cooling demonstrates intercollicular modulation of neuronal activity.

The auditory pathways coursing through the brainstem are organized bilaterally in mirror image about the midline and at several levels the two sides are interconnected. One of the most prominent points of interconnection is the commissure of the inferior colliculus (CoIC). Anatomical studies have revealed that these fibers make reciprocal connections which follow the tonotopic organization of the inferior colliculus (IC), and that the commissure contains both excitatory and, albeit fewer, inhibitory fibers. The role of these connections in sound processing is largely unknown. Here we describe a method to address this question in the anaesthetized guinea pig. We used a cryoloop placed on one IC to produce reversible deactivation while recording electrophysiological responses to sounds in both ICs. We recorded single units, multi-unit clusters and local field potentials (LFPs) before, during and after cooling. The degree and spread of cooling was measured with a thermocouple placed in the IC and other auditory structures. Cooling sufficient to eliminate firing was restricted to the IC contacted by the cryoloop. The temperature of other auditory brainstem structures, including the contralateral IC and the cochlea were minimally affected. Cooling below 20°C reduced or eliminated the firing of action potentials in frequency laminae at depths corresponding to characteristic frequencies up to ~8 kHz. Modulation of neural activity also occurred in the un-cooled IC with changes in single unit firing and LFPs. Components of LFPs signaling lemniscal afferent input to the IC showed little change in amplitude or latency with cooling, whereas the later components, which likely reflect inter- and intra-collicular processing, showed marked changes in form and amplitude. We conclude that the cryoloop is an effective method of selectively deactivating one IC in guinea pig, and demonstrate that auditory processing in the IC is strongly influenced by the other.

Age-related changes in the acoustic startle reflex in Fischer 344 and Long Evans rats.

The behavioral consequences of age-related changes in the auditory system were studied in Fischer 344 (F344) rats as a model of fast aging and in Long Evans (LE) rats as a model of normal aging. Hearing thresholds, the strength of the acoustic startle responses (ASRs) to noise and tonal stimuli, and the efficiency of the prepulse inhibition (PPI) of ASR were assessed in young-adult, middle-aged, and aged rats of both strains. Compared with LE rats, F344 rats showed larger age-related hearing threshold shifts, and the amplitudes of their startle responses were mostly lower. Both rat strains demonstrated a significant decrease of startle reactivity during aging. For tonal stimuli, this decrease occurred at an earlier age in the F344 rats: middle-aged F344 animals expressed similar startle reactivity as aged F344 animals, whereas middle-aged LE animals had similar startle reactivity as young-adult LE animals. For noise stimuli, on the other hand, a similar progression of age-related ASR changes was found in both strains. No significant relationship between the hearing thresholds and the ASR amplitudes was found within any age group. Auditory PPI was less efficient in F344 rats than in LE rats. An age-related reduction of the PPI of ASR was observed in rats of both strains; however, a significant reduction of PPI occurred only in aged rats. The results indicate that the ASR may serve as an indicator of central presbycusis.