The development of spatial behaviour and the hippocampal neural representation of space

The role of the hippocampal formation in spatial cognition is thought to be supported by distinct classes of neurons whose firing is tuned to an organism's position and orientation in space. In this article, we review recent research focused on how and when this neural representation of space emerges during development: each class of spatially tuned neurons appears at a different age, and matures at a different rate, but all the main spatial responses tested so far are present by three weeks of age in the rat. We also summarize the development of spatial behaviour in the rat, describing how active exploration of space emerges during the third week of life, the first evidence of learning in formal tests of hippocampus-dependent spatial cognition is observed in the fourth week, whereas fully adult-like spatial cognitive abilities require another few weeks to be achieved. We argue that the development of spatially tuned neurons needs to be considered within the context of the development of spatial behaviour in order to achieve an integrated understanding of the emergence of hippocampal function and spatial cognition

Place Cell Networks in Pre-weanling Rats Show Associative Memory Properties from the Onset of Exploratory Behavior

Place cells are hippocampal pyramidal cells that are active when an animal visits a restricted area of the environment, and collectively their activity constitutes a neural representation of space. Place cell populations in the adult rat hippocampus display fundamental properties consistent with an associative memory network: the ability to 1) generate new and distinct spatial firing patterns when encountering novel spatial contexts or changes in sensory input ("remapping") and 2) reinstate previously stored firing patterns when encountering a familiar context, including on the basis of an incomplete/degraded set of sensory cues ("pattern completion"). To date, it is unknown when these spatial memory responses emerge during brain development. Here, we show that, from the age of first exploration (postnatal day 16) onwards, place cell populations already exhibit these key features: they generate new representations upon exposure to a novel context and can reactivate familiar representations on the basis of an incomplete set of sensory cues. These results demonstrate that, as early as exploratory behaviors emerge, and despite the absence of an adult-like grid cell network, the developing hippocampus processes incoming sensory information as an associative memory network

Strategies and outcomes of HIV status disclosure in HIV-positive young women with abuse histories

Young women with HIV and histories of physical and/or sexual abuse in childhood may be vulnerable to difficulties with disclosure to sexual partners. Abuse in childhood is highly prevalent in HIV-positive women, and has been associated with poorer communication, low assertiveness, low self worth, and increased risk for sexual and other risk behaviors that increase the risk of secondary transmission of HIV. HIV disclosure may be an important link between abuse and sexual risk behaviors. Qualitative interviews with 40 HIV-positive young women with childhood physical and/or sexual abuse were conducted; some women had also experienced adult victimization. Results suggest that HIV-positive women with abuse histories use a host of strategies to deal with disclosure of HIV status, including delaying disclosure, assessing hypothetical responses of partners, and determining appropriate stages in a relationship to disclose. Stigma was an important theme related to disclosure. We discuss how these disclosure processes impact sexual behavior and relationships and discuss intervention opportunities based on our findings

Coordinated Emergence of Hippocampal Replay and Theta Sequences during Post-natal Development

Hippocampal place cells encode an animal's current position in space during exploration [1]. During sleep, hippocampal network activity recapitulates patterns observed during recent experience: place cells with overlapping spatial fields show a greater tendency to co-fire ("reactivation") [2], and temporally ordered and compressed sequences of place cell firing observed during wakefulness are reinstated ("replay") [3-5]. Reactivation and replay may underlie memory consolidation [6-10]. Compressed sequences of place cell firing also occur during exploration: during each cycle of the theta oscillation, the set of active place cells shifts from those signaling positions behind to those signaling positions ahead of an animal's current location [11, 12]. These "theta sequences" have been linked to spatial planning [13]. Here, we demonstrate that, before weaning (post-natal day [P]21), offline place cell activity associated with sharp-wave ripples (SWRs) reflects predominantly stationary locations in recently visited environments. By contrast, sequential place cell firing, describing extended trajectories through space during exploration (theta sequences) and subsequent rest (replay), emerge gradually after weaning in a coordinated fashion, possibly due to a progressive decrease in the threshold for experience-driven plasticity. Hippocampus-dependent learning and memory emerge late in altricial mammals [14-17], appearing around weaning in rats and slowly maturing thereafter [14,15]. In contrast, spatially localized firing is observed 1 week earlier (with reduced spatial tuning and stability) [18-21]. By examining the development of hippocampal reactivation, replay, and theta sequences, we show that the coordinated maturation of offline consolidation and online sequence generation parallels the late emergence of hippocampal memory in the rat

Examining how health navigation affects mental health among gay, bisexual, and other men who have sex with men living with human immunodeficiency virus in Guatemala

Gay, bisexual, and other men who have sex with men (GBMSM) are disproportionately affected by mental health problems and human immunodeficiency virus (HIV). Health navigation has the potential to improve both HIV and mental health outcomes; however, few studies have measured the impact of navigation on mental health among people living with HIV. We analyzed longitudinal data from a sociobehavioral survey and navigation monitoring system with GBMSM living with HIV in Guatemala (n = 346) that participated in a 12-month differentiated care intervention. We examined relationships between navigation characteristics (frequency, duration, mode of interactions, and level of emotional, instrumental, and informational navigation support) and anxiety and depression using fixed-effects regression. We also examined if these relationships were moderated by baseline social support. We found that as navigation interactions increased, anxiety significantly improved [B = -0.03, standard error (SE) = 0.01 p = 0.05]. Participants who received high levels of informational navigator support also experienced a significant improvement in anxiety compared with those receiving low levels of informational support (B = -0.81, SE = 0.40, p = 0.04). Unexpectedly, we found that as the proportion of in-person navigation interactions increased, anxiety worsened (B = 1.12, SE = 0.54, p = 0.04). No aspects of navigation were significantly associated with depression and baseline social support did not moderate the relationship between navigation and anxiety and depression. To improve the mental health of key populations affected by HIV, health navigation programs should prioritize frequent interaction and informational navigation support for clients with anxiety while considering other strategies that specifically target reducing depressive symptoms, including other cost-effective modalities, such as mobile apps

Willingness to act upon beliefs about 'treatment as prevention' among Australian gay and bisexual men

HIV 'treatment as prevention' (TasP) is highly effective in reducing HIV transmission in serodiscordant couples. There has been little examination of gay and bisexual men's attitudes towards TasP, particularly regarding men's willingness to act on beliefs about TasP. We conducted an online cross-sectional survey of Australian men in late 2012 to investigate knowledge and beliefs about new developments in HIV prevention. Amongst 839 men (mean age 39.5 years), men tended to disagree that TasP was sufficiently effective to justify reduced condom use, although HIV-positive men had more favourable attitudes. Only a minority of men were aware of any evidence for TasP; and one-quarter incorrectly believed that evidence for the effectiveness of TasP already existed for the homosexual population. One-fifth (20.5%) of men reported that they would be willing to have condomless anal intercourse with an opposite-status sexual partner when the HIV-positive partner was taking HIV treatments. Factors independently associated with such willingness were: HIV-positive serostatus, reporting any serodiscordant or serononconcordant condomless anal intercourse with a regular male partner in the previous six months, reporting any condomless anal intercourse with a casual male partner in the previous six months, and having greater beliefs in the effectiveness of TasP. This indicated that the men most willing to rely on TasP to prevent transmission were already engaging in higher risk practices. Biomedical HIV prevention represents a rapidly changing environment with new research as well as community and policy responses emerging at a fast pace. For men with serodiscordant sexual partners to successfully apply TasP to reducing transmission risk, more support and education is needed to enable better utilisation of TasP in specific relational and sexual contexts

An instant messaging mobile phone application for promoting HIV pre-exposure prophylaxis uptake among Chinese gay, bisexual and other men who have sex with men: A mixed methods feasibility and piloting randomized controlled trial study

Background Mobile health (mHealth) is a promising intervention mode for HIV prevention, but little is known about its feasibility and effects in promoting pre-exposure prophylaxis (PrEP) uptake among Chinese gay, bisexual and other men who have sex with men (GBMSM). Methods We evaluated an instant messaging application using a WeChat-based mini-app to promote PrEP uptake among GBMSM via a mixed-methods design that includes a 12-week, two-arm randomized controlled pilot trial and in-depth progress interviews in Guangzhou, China. Primary outcomes include the number of PrEP initiations, individual-level psychosocial variables related to PrEP initiation, and usability of the PrEP mini-app. Results Between November 2020 and April 2021, 70 GBMSM were successfully enrolled and randomized into two arms at 2:1 ratio (46 to the intervention arm, 24 to the control arm). By the end of 12-week follow-up, 22 (31.4%) participants completed the initial consultation and lab tests for PrEP, and 13 (18.6%) filled their initial PrEP prescription. We observed modest but non-significant improvements in participants’ intention to use PrEP, actual PrEP initiation, PrEP-related self-efficacy, stigma, and attitudes over 12 weeks when comparing the mini-app and the control arms. Qualitative interviews revealed the key barriers to PrEP uptake include anticipated stigma and discrimination in clinical settings, burden of PrEP care, and limited operating hours of the PrEP clinic. In-person clinic navigation support was highly valued. Conclusions This pilot trial of a mobile phone-based PrEP mini-app demonstrated feasibility and identified limitations in facilitating PrEP uptake among Chinese GBMSM. Future improvements may include diversifying the content presentation in engaging media formats, adding user engagement features, and providing off-line in-clinic navigation support during initial PrEP visit. More efforts are needed to understand optimal strategies to identify and implement alternative PrEP provision models especially in highly stigmatized settings with diverse needs. Trial registration Trial registration: The study was prospectively registered on clinicaltrials.gov (NCT04426656) on 11 June, 2020

A TauP301L mouse model of dementia; development of pathology, synaptic transmission, microglial response and cognition throughout life

Background: Late stage Alzheimer's disease and other dementias are associated with neurofibrillary tangles and neurodegeneration. Here we describe a mouse (TauD35) carrying human Tau with the P301L mutation that results in Tau hyperphosphorylation and tangles. Previously we have compared gene expression in TauD35 mice to mice which develop plaques but no tangles. A similar comparison of other pathological features throughout disease progression is made here between amyloidβ and Tau mice. Methods: In vitro CA1 patch clamp and field recordings were used to investigate synaptic transmission and plasticity. Plaque load and microglia were investigated with immunohistochemistry. Cognition, locomotor activity and anxiety-related behaviours were assessed with a forced-alternation T-maze, open field and light/dark box. Results: Transgene copy number in TauD35 mice fell into two groups (HighTAU and LowTAU), allowing assessment of dose-dependent effects of overexpression and resulting in tangle load increasing 100-fold for a 2-fold change in protein levels. Tangles were first detected at 8 (HighTAU) or 13 months (LowTAU) but the effects on synaptic transmission and plasticity and behaviour were subtle. However severe neurodegeneration occurred in HighTAU mice at around 17 months preceded by considerable proliferation but little additional activation of microglia. Proliferation only started as neurodegeneration began at 13 months. Similarly to HighTau mice at 13 months of age, LowTAU mice at 24 months of age showed a comparable tangle load and microglial proliferation. However, LowTAU mice showed no neurodegeneration at this stage and considerable microglial activation, stressing the dependence of these effects on overexpression and/or age. Conclusions: Comparison of the effects of amyloidβ and plaques without tangles in a model of preclinical Alzheimer's disease to the effects of tangles without amyloidβ plaques in the late stage model described here may clarify the progressive stages of Alzheimer's disease. While Tau hyperphosphorylation and neurofibrillary tangles are eventually sufficient to cause severe neurodegeneration, initial effects on synaptic transmission and the immune response are subtle. In contrast while even with a heavy plaque load little if any neurodegeneration occurs, considerable effects on synaptic transmission and the immune system result, even before plaques are detectable

Tough Talks COVID-19 Digital Health Intervention for Vaccine Hesitancy Among Black Young Adults: Protocol for a Hybrid Type 1 Effectiveness Implementation Randomized Controlled Trial

Background Interventions for increasing the uptake of COVID-19 vaccination among Black young adults are central to ending the pandemic. Black young adults experience harms from structural forces, such as racism and stigma, that reduce receptivity to traditional public health messaging due to skepticism and distrust. As such, Black young adults continue to represent a priority population on which to focus efforts for promoting COVID-19 vaccine uptake. Objective In aims 1 and 2, the Tough Talks digital health intervention for HIV disclosure will be adapted to address COVID-19 vaccine hesitancy and tailored to the experiences of Black young adults in the southern United States (Tough Talks for COVID-19). In aim 3, the newly adapted Tough Talks for COVID-19 digital health intervention will be tested across the following three southern states: Alabama, Georgia, and North Carolina. Methods Our innovative digital health intervention study will include qualitative and quantitative assessments. A unique combination of methodological techniques, including web-based surveys, choose-your-own-adventures, digital storytelling, user acceptability testing, and community-based participatory approaches, will culminate in a 2-arm hybrid type 1 effectiveness implementation randomized controlled trial, wherein participants will be randomized to the Tough Talks for COVID-19 intervention arm or a standard-of-care control condition (N=360). Logistic regression will be used to determine the effect of the treatment arm on the probability of vaccination uptake (primary COVID-19 vaccine series or recommended boosters). Concurrently, the inner and outer contexts of implementation will be ascertained and catalogued to inform future scale-up. Florida State University’s institutional review board approved the study (STUDY00003617). Results Our study was funded at the end of April 2021. Aim 1 data collection concluded in early 2022. The entire study is expected to conclude in January 2025. Conclusions If effective, our digital health intervention will be poised for broad, rapid dissemination to reduce COVID-19 mortality among unvaccinated Black young adults in the southern United States. Our findings will have the potential to inform efforts that seek to address medical mistrust through participatory approaches. The lessons learned from the conduct of our study could be instrumental in improving health care engagement among Black young adults for several critical areas that disproportionately harm this community, such as tobacco control and diabetes prevention. Trial Registration ClinicalTrials.gov NCT05490329; https://clinicaltrials.gov/ct2/show/NCT05490329 International Registered Report Identifier (IRRID) DERR1-10.2196/4124

Effects of rising amyloidβ levels on hippocampal synaptic transmission, microglial response and cognition in APP_{Swe}/PSEN1_{M146V} transgenic mice

BACKGROUND: Progression of Alzheimer's disease is thought initially to depend on rising amyloidβ and its synaptic interactions. Transgenic mice (TASTPM; APP_{Swe}/PSEN1_{M146V}) show altered synaptic transmission, compatible with increased physiological function of amyloidβ, before plaques are detected. Recently, the importance of microglia has become apparent in the human disease. Similarly, TASTPM show a close association of plaque load with upregulated microglial genes. METHODS: CA1 synaptic transmission and plasticity were investigated using in vitro electrophysiology. Microglial relationship to plaques was examined with immunohistochemistry. Behaviour was assessed with a forced-alternation T-maze, open field, light/dark box and elevated plus maze. FINDINGS: The most striking finding is the increase in microglial numbers in TASTPM, which, like synaptic changes, begins before plaques are detected. Further increases and a reactive phenotype occur later, concurrent with development of larger plaques. Long-term potentiation is initially enhanced at pre-plaque stages but decrements with the initial appearance of plaques. Finally, despite altered plasticity, TASTPM have little cognitive deficit, even with a heavy plaque load, although they show altered non-cognitive behaviours. INTERPRETATION: The pre-plaque synaptic changes and microglial proliferation are presumably related to low, non-toxic amyloidβ levels in the general neuropil and not directly associated with plaques. However, as plaques grow, microglia proliferate further, clustering around plaques and becoming phagocytic. Like in humans, even when plaque load is heavy, without development of neurofibrillary tangles and neurodegeneration, these alterations do not result in cognitive deficits. Behaviours are seen that could be consistent with pre-diagnosis changes in the human condition. FUNDING: GlaxoSmithKline; BBSRC; UCL; ARUK; MRC