Trends in opioid toxicities among people with and without opioid use disorder and the impact of the COVID-19 pandemic in Ontario, Canada: A population-based analysis.

BACKGROUND: Across Canada, the COVID-19 pandemic occurred amidst an ongoing drug toxicity crisis. Although elevated rates of substance-related harms have been observed nationally, it remains unknown if the pandemic state of emergency led to disproportionate increases in opioid toxicities among people with opioid use disorder (OUD) compared to those without. METHODS: We conducted a population-based repeated cross-sectional time series analysis of fatal and non-fatal opioid toxicities between January 1, 2014, and December 31, 2021, in Ontario, Canada. We used interventional autoregressive integrated moving average models to examine the impact of the pandemic on monthly rates of opioid toxicities per 100,000 Ontario residents stratified by people with and without OUD. RESULTS: We identified 80,296 opioid toxicities of which 53.5 % occurred among people with OUD. Among 52,052 unique individuals, 60.5 % were male and 46.2 % were 25-44 years old. Between January 2014 and December 2021, the rate of opioid toxicities increased from 2.6 to 10.5 per 100,000 (rate ratio [RR]=4.07). The magnitude of this increase differed among people with OUD (0.8 to 7.4 per 100,000; RR=9.35) and without OUD (1.8 to 3.1 per 100,000; RR=1.74). We observed a significant ramp increase in the overall rate of opioid toxicities following the declaration of the pandemic emergency in March 2020 (+0.19 per 100,000 monthly, 95 % CI: 0.029, 0.36, p = 0.021). In a stratified analysis, we found a similar ramp increase among people with OUD (+0.19 per 100,000 monthly, 95 % CI: 0.10, 0.28, p < 0.001); however, this was not observed among people without OUD (p = 0.95). CONCLUSIONS: The rate of opioid toxicities accelerated across Ontario following the pandemic-related state of emergency, with the majority of this increase among people with OUD. The important differences observed among people with OUD compared with those without, highlights the critical need for improved access to harm reduction and treatment interventions among this population.

Characteristics, treatment patterns and retention with extended-release subcutaneous buprenorphine for opioid use disorder: A population-based cohort study in Ontario, Canada.

BACKGROUND: Uptake and retention for opioid agonist treatment (OAT) remains low. Novel extended-release formulations may improve OAT accessibility by reducing the frequency of healthcare visits. Our aim was to examine uptake, characteristics, treatment patterns and retention of individuals initiating extended-release subcutaneous buprenorphine (BUP-ER), a monthly injectable OAT. METHODS: We conducted a population-based cohort study among adults aged 18+ initiated on BUP-ER between February 3, 2020 and March 31, 2022 in Ontario, Canada. Using administrative health data, we defined continuous BUP-ER use based on repeat injections within a 56-day period and used Kaplan-Meier curves to estimate time on treatment. Among new BUP-ER recipients, we described individual and prescriber characteristics, healthcare utilization and treatment patterns. RESULTS: 2366 individuals initiated BUP-ER. The median time to BUP-ER discontinuation was 183 days (interquartile range: 66-428 days) and 52.0% of individuals were co-prescribed buprenorphine/naloxone at least once throughout the period of BUP-ER receipt. Among individuals who initiated on a dose of 300mg BUP-ER and had three or more injections, 18.8% continued to receive only 300mg doses (N=276 of 1470). Furthermore, 28.6% of those whose dose was reduced to 100mg (N=341 of 1194) had a subsequent dose increase to 300mg. CONCLUSIONS: On average, people initiating BUP-ER discontinue within the first 6 months of treatment. While BUP-ER is likely providing an important OAT option, the high occurrence of discontinuation, supplementation with buprenorphine/naloxone, and frequent dose increases suggest inadequacy of current dosing recommendations among a proportion of individuals.

Evaluation of the gap in delivery of opioid agonist therapy among individuals with opioid-related health problems: a population-based retrospective cohort study.

AIMS: Although opioid-related harms have reached new heights across North America, the size of the gap in opioid agonist therapy (OAT) delivery for opioid-related health problems is unknown in most jurisdictions. This study sought to characterize the gap in OAT treatment using a cascade of care framework, and determine factors associated with engagement and retention in treatment. DESIGN: A population-based retrospective cohort study. SETTING: Ontario, Canada. PARTICIPANTS: Individuals who sought medical care for opioid-related health problems or died from an opioid-related cause between 2005 and 2019. MEASUREMENTS: Monthly treatment status for buprenorphine/naloxone or methadone OAT between 2013 and 2019 (i.e. 'off OAT', 'retained on OAT < 6 months', 'retained on OAT ≥ 6 months'). FINDINGS: Of 122 811 individuals in the cohort, 97 516 (79.4%) received OAT at least once during the study period. There was decreasing 6-month treatment retention over time. Model results indicated that males had higher odds of being on OAT each month [odds ratio (OR) = 1.26, 95% confidence interval (CI) = 1.23-1.28] but lower odds of OAT retention (OR = 0.90, 95% CI = 0.88-0.92), while the reverse was observed for older individuals (monthly: OR = 0.76 per 10-year increase, 95% CI = 0.76-0.77; retention: OR = 1.36 per 10-year increase, 95% CI = 1.34-1.38) and individuals with higher neighbourhood income (e.g. highest income quintile, monthly: OR = 0.79, 95% CI = 0.77-0.82; highest income quintile, retention: OR = 1.15, 95% CI = 1.11-1.20). Individuals residing in rural areas and with a history of mental health diagnoses had poorer outcomes overall, including lower odds of being on OAT each month (rural: OR = 0.75, 95% CI = 0.73-0.78; mental health: OR = 0.89, 95% CI = 0.87-0.92) and OAT retention (rural: OR = 0.79, 95% CI = 0.77-0.82; mental health: OR = 0.81, 95% CI = 0.78-0.83), as well as higher risk of starting/stopping OAT [rural, starting OAT: hazard ratio (HR) = 1.07, 95% CI = 1.05-1.10; mental health, starting OAT: HR = 1.20, 95% CI: 1.18-1.23; rural, stopping OAT: HR = 1.24, 95% CI: = 1.22-1.26; mental health, stopping OAT: HR = 1.11, 95% CI = 1.09-1.13]. Individuals with a history of mental health diagnoses also had a higher risk of death, regardless of OAT status (off OAT death: HR = 1.49, 95% CI = 1.33-1.66; on OAT death: HR = 1.20, 95% CI = 1.09-1.31). CONCLUSIONS: Factors influencing engagement and declining retention in treatment with opioid agonist therapy in Ontario's health system include age, sex and neighbourhood income, as well as mental health diagnoses or residing in rural regions.

Impact of a publicly funded pharmacy-dispensed naloxone program on fatal opioid overdose rates: A population-based study.

BACKGROUND: Studies examining the impact of pharmacy-dispensed naloxone programs on fatal opioid overdose rates are lacking. We examined the impact of the publicly funded Ontario Naloxone Program for Pharmacies (ONPP), implemented in June 2016, on provincial rates of opioid overdose deaths. METHODS: We conducted a population-based interrupted time-series study between July 1, 2012 and December 31, 2018. We considered a parsimonious model with terms for time, ONPP implementation, and time following the ONPP implementation. Models were adjusted for population characteristics, number of pharmacies and rate of naloxone distributed through non-pharmacy sites within provincial public health units. RESULTS: In the parsimonious model, the ONPP was associated with a non-significant 9% reduction in the level of fatal opioid overdoses (rate ratio [RR] 0.91; 95% confidence interval [CI] 0.79-1.06), a finding that was most pronounced in regions in the lowest tertile of implementation (RR 0.75; 95% CI 0.62-0.91). Following multivariable adjustment, there was an increase in the level (RR 1.06; 95% CI 0.94-1.19) and slope change (RR 1.06; 95% CI 1.02-1.10) of fatal overdose rates. CONCLUSION: The ONPP is insufficient as a single intervention to meaningfully reduce rates of fatal opioid overdoses during a period in which the cause of these deaths shifted from prescription opioids to highly potent fentanyl analogs. Access to additional harm reduction, treatment, and other interventions is necessary to prevent deaths and optimize the health of people who use drugs.

Impact of the COVID-19 pandemic on the prevalence of opioid agonist therapy discontinuation in Ontario, Canada: A population-based time series analysis.

BACKGROUND: We assessed the impact of COVID-19, which includes the declaration of a state of emergency and subsequent release of pandemic-specific OAT guidance (March 17, 2020 to March 23, 2020) on the prevalence of OAT discontinuation. METHODS: We conducted a population-based time series analysis using interventional autoregressive integrated moving average models among Ontario residents who were stable (>60 days of continuous use) and not yet stable on OAT. Specifically, we examined whether COVID-19 impacted the weekly percentage of individuals who discontinued OAT, overall and stratified by treatment type (methadone vs. buprenorphine/naloxone). Additionally, we compared demographic characteristics and patient outcomes among people stable on OAT who discontinued treatment during (March 17, 2020 to November 30, 2020) and prior (July 3, 2019 to March 16, 2020) to the pandemic. RESULTS: The weekly prevalence of OAT discontinuation across the study period ranged between 0.6% and 1.1%, among those stable on treatment compared to 7.3% and 16.6%, among those not stable on treatment. Following COVID-19, there was no significant change in the percentage of Ontarians who discontinued OAT, regardless of whether they were stabilized on treatment. Among those stable on OAT, a similar proportion of patients restarted therapy and experienced opioid-related harm following an OAT discontinuation. However, mortality following OAT discontinuation must be noted, as approximately 1.4% and 0.8% of people who discontinued methadone and buprenorphine/naloxone respectively, died within 30 days of discontinuation. CONCLUSIONS: Trends in the prevalence of OAT discontinuation did not significantly change during the first eight months of the COVID-19 pandemic.

Impact of the COVID-19 pandemic on the provision of take-home doses of opioid agonist therapy in Ontario, Canada: A population-based time-series analysis.

BACKGROUND: In March 2020, the Ontario government declared a state of emergency due to the growing risk of COVID-19. In response, new guidance for the management of opioid agonist therapy (OAT) was released, which included the expansion of eligibility for take-home doses. We investigated the impact of these changes on trends in the distribution of take-home doses of OAT. METHODS: We conducted a population-based time series analysis among residents of Ontario, Canada who were dispensed OAT between June 25, 2019 and November 30, 2020. For each week of the study period, we calculated the percentage of people dispensed (a) methadone and (b) buprenorphine/naloxone by the number of take-home doses received. We used interventional autoregressive integrated moving average models to estimate changes in the percentage of people dispensed each category of take-home doses in the weeks following the declaration of the state of emergency and release of the OAT dispensing guidance. RESULTS: Following the state of emergency and release of the OAT dispensing guidance, there was a significant increase in the percentage of Ontarians dispensed 7 to 13 (3.6% increase; p = 0.033) and 14 or more (0.8% increase; p<0.001) take-home doses of methadone, and in the percentage of people dispensed 7 to 13 (4.3% increase; p = 0.001), 14 to 27 (2.8% increase; p<0.001), and 28 or more (0.3% increase; p = 0.008) take-home doses of buprenorphine/naloxone. There were significant decreases in the percentage of Ontarians receiving daily dispensed buprenorphine/naloxone (-3.1%; p = 0.001), as well as the percentage dispensed 1 to 6 take-home doses of methadone (-4.5%; p = 0.001) and buprenorphine/naloxone (-4.9%; p = 0.001). CONCLUSION: The new guidance for dispensing OAT in Ontario resulted in increases in the duration of take-home doses of methadone and buprenorphine/naloxone supplied. However, given that changes were small, strategies to improve retention in OAT and ensure equitable access to take-home dosing should continue.

Association Between Increased Dispensing of Opioid Agonist Therapy Take-Home Doses and Opioid Overdose and Treatment Interruption and Discontinuation.

Importance: During the COVID-19 pandemic, modified guidance for opioid agonist therapy (OAT) allowed prescribers to increase the number of take-home doses to promote treatment retention. Whether this was associated with an increased risk of overdose is unclear. Objective: To evaluate whether increased take-home doses of OAT early in the COVID-19 pandemic was associated with treatment retention and opioid-related harm. Design, Setting, and Participants: A retrospective propensity-weighted cohort study of 21 297 people actively receiving OAT on March 21, 2020, in Ontario, Canada. Changes in OAT take-home dose frequency were assessed between March 22, 2020, and April 21, 2020, and individuals were observed for up to 180 days to assess outcomes (last date of follow-up, October 18, 2020). Exposures: Exposure was defined as extended take-home doses in the first month of the pandemic within each of 4 cohorts based on OAT type and baseline take-home dose frequency (daily dispensed methadone, 5-6 take-home doses of methadone, daily dispensed buprenorphine/naloxone, and 5-6 take-home doses of buprenorphine/naloxone). Main Outcomes and Measures: Primary outcomes were opioid overdose, interruption in OAT, and OAT discontinuation. Results: Among 16 862 methadone and 4435 buprenorphine/naloxone recipients, the median age ranged between 38 and 42 years, and 29.1% to 38.2% were women. Among individuals receiving daily dispensed methadone (n = 5852), initiation of take-home doses was significantly associated with lower risks of opioid overdose (6.9% vs 9.5%/person-year; weighted hazard ratio [HR], 0.73 [95% CI, 0.56-0.96]), treatment discontinuation (51.0% vs 63.6%/person-year; weighted HR, 0.80 [95% CI, 0.72-0.90]), and treatment interruption (19.0% vs 23.9%/person-year; weighted HR, 0.80 [95% CI, 0.67-0.95]) compared with no change in take-home doses. Among individuals receiving daily dispensed buprenorphine/naloxone (n = 662), there was no significant difference in any outcomes between exposure groups. Among individuals receiving weekly dispensed OAT (n = 11 010 for methadone; n = 3773 for buprenorphine/naloxone), extended take-home methadone doses were significantly associated with lower risks of OAT discontinuation (14.1% vs 19.6%/person-year; weighted HR, 0.72 [95% CI, 0.62-0.84]) and interruption in therapy (5.1% vs 7.4%/person-year; weighted HR, 0.69 [95% CI, 0.53-0.90]), and extended take-home doses of buprenorphine/naloxone were significantly associated with lower risk of interruption in therapy (9.5% vs 12.9%/person-year; weighted HR, 0.74 [95% CI, 0.56-0.99]) compared with no change in take-home doses. Other primary outcomes were not significantly different between groups. Conclusions and Relevance: In Ontario, Canada, during the COVID-19 pandemic, dispensing of increased take-home doses of opioid agonist therapy was significantly associated with lower rates of treatment interruption and discontinuation among some subsets of patients receiving opioid agonist therapy, and there were no statistically significant increases in opioid-related overdoses over 6 months of follow-up. These findings may be susceptible to residual confounding and should be interpreted cautiously.

Duration of use and outcomes among people with opioid use disorder initiating methadone and buprenorphine in Ontario: a population-based propensity-score matched cohort study.

AIMS: To characterize comparative risks and benefits of methadone versus buprenorphine/naloxone in a contemporary cohort where the unregulated drug supply is dominated by fentanyl. DESIGN, SETTING AND PARTICIPANTS: Population-based propensity-score matched cohort study conducted in Ontario, Canada among people aged 18+ initiating opioid agonist therapy (OAT) for an opioid use disorder between October 2016 and December 2018 (n = 18 880). INTERVENTION: Initiation of methadone versus buprenorphine/naloxone. MEASUREMENTS: The primary outcome was opioid overdose (fatal and non-fatal) while on treatment, with secondary outcomes including opioid overdose (first 30 days of treatment), treatment discontinuation, health-care interactions related to treatment of opioid use disorder, receiving a weekly supply of take-home doses and opioid overdose within 30 days of treatment discontinuation. Outcomes were assessed over 1 year. FINDINGS: Overall, 7517 people initiating buprenorphine were matched to an equal number of methadone-treated individuals. Risk of opioid overdose while on treatment [hazard ratio (HR) = 0.50; 95% confidence interval (CI) = 0.37-0.68] or within the first 30 days of treatment (HR = 0.51, 95% CI = 0.31-0.85) was lower among buprenorphine recipients compared to methadone recipients. In secondary analyses, people initiating buprenorphine had a higher risk of treatment discontinuation within the first year (median time to discontinuation 104 versus 265 days, HR = 1.43, 95% CI = 1.37-1.49), had lower rates of health-care interactions for OUD (186.4 versus 254.3 per person-year; rate ratio = 0.73; 95% CI = 0.72-0.75), and a higher rate of receiving weekly take-home doses (HR = 2.33; 95% CI = 2.20-2.46). Overdose rates in the period following OAT discontinuation were higher than those observed while on treatment, but did not differ significantly by OAT type. CONCLUSIONS: Although treatment retention is higher among methadone recipients, overdose risk is also elevated compared to buprenorphine recipients. These findings demonstrate the benefits of any OAT on avoidance of overdose, particularly following treatment discontinuation and with the increasingly unpredictable drug supply in North America.

A qualitative study of a publicly funded pharmacy-dispensed naloxone program.

AIMS: To characterize the experiences of individuals accessing pharmacy-based naloxone and relate these experiences to the risk environments and discourses in which they are embedded. METHODS: We conducted a qualitative study using in-depth interviews of 37 adults aged 18 years and over who had accessed pharmacy-dispensed naloxone. Participants were recruited from across Ontario, Canada, and comprised individuals taking opioids for chronic pain, those taking opioids for reasons other than chronic pain, and individuals acquiring naloxone to act as bystanders in an opioid overdose setting. We drew upon risk environment theory to interpret participants' accounts. RESULTS: Following analysis and interpretation, we generated five theoretically-informed themes characterizing the experiences of individuals accessing pharmacy-dispensed naloxone: 'intersection of naloxone narrative with pharmacy environment', 'individual risk environment and pharmacy-dispensed naloxone uptake', 'safe spaces: creating an enabling environment for pharmacy-dispensed naloxone', 'individuation: becoming a first responder' and 'beyond naloxone: the macro risk environment'. Specifically, participants described how judgement and stereotyping associated with the broader naloxone narrative can be amplified in the space of the pharmacy, leading to fears of reprisals and strategies to mitigate social risk. In addition, the social construction of naloxone as a drug for 'problematic' opioid use and a lack of pharmacist awareness regarding the risk environments in which opioid use occurs was perceived to limit opportunities for optimizing naloxone distribution and training. Finally, participants described approaches that could create enabling environments in the space of the pharmacy while remaining cognizant of the structural changes required in the macro risk environments of people who take opioids. CONCLUSIONS: Despite increasing the availability of naloxone, participants characterized several social and environmental factors that could limit the accessibility of the drug from pharmacies. Strategies to address these factors could create enabling environments within pharmacies that optimize the reach and impact of pharmacy-dispensed naloxone.

Impact of policy changes on the provision of naloxone by pharmacies in Ontario, Canada: a population-based time-series analysis.

BACKGROUND AND AIMS: In June 2016, the Ontario, Canada government implemented the Ontario Naloxone Program for Pharmacies (ONPP), authorizing pharmacists to provide injectable naloxone kits at no charge to all Ontario residents. In March 2018, the program was amended to include intranasal naloxone and remove the requirement to present a government health card to the dispensing pharmacist. We examined whether these changes increased naloxone dispensing through the ONPP. DESIGN: Population-based time-series analysis using interventional autoregressive integrated moving average models. SETTING: Ontario, Canada. PARTICIPANTS: All Ontario residents between 1 July 2016 and 31 March 2020. MEASUREMENTS: Monthly rates of pharmacy naloxone dispensing. FINDINGS: Overall, 199 484 individuals were dispensed a naloxone kit during the study period. In the main analysis, the rate of pharmacy naloxone dispensing increased by 65.1% following program changes (55.6-91.8 kits per 100 000 population between February 2018 and May 2018; P = 0.01). In subgroup analyses, naloxone dispensing increased among individuals receiving opioid agonist therapy (OAT) (3374.9-7264.2 kits per 100 000 OAT recipients; P = 0.04) among individuals receiving other prescription opioids (192.8-381.8 kits per 100 000 population prescribed opioids; P < 0.01), among individuals with past opioid exposure (134.7-205.6 kits per 100 000 population with past opioid exposure; P < 0.01) and in urban centers (56.2-91.4 kits per 100 000 population; P < 0.01). We did not observe a clear impact on pharmacy-dispensed naloxone to individuals with no or unknown opioid exposure (34.4-39.3 kits per 100 000 population with no/unknown opioid exposure; P = 0.42) and in rural regions (50.4-97.2 kits per 100 000 population; P = 0.09). CONCLUSIONS: Changes to the Ontario Naloxone Program for Pharmacies to add intranasal naloxone and remove the requirement to present a government health card appeared to increase pharmacy-based naloxone dispensing uptake in Ontario, Canada, particularly among individuals at high risk of inadvertent opioid overdose.

Geographic variation in the provision of naloxone by pharmacies in Ontario, Canada: A population-based small area variation analysis.

BACKGROUND: Regional variation in pharmacy-dispensed naloxone rates could create access disparities that undermine the effectiveness of this approach. We explored individual and public health unit (PHU)-level determinants of regional variation in naloxone distribution through the Ontario Naloxone Program for Pharmacies. METHODS: We conducted a population-based study between April 1, 2017 and March 31, 2018. We calculated age- and sex-standardized pharmacy-dispensed naloxone rates for the 35 Ontario PHUs, and identified determinants of these rates using generalized estimating equations negative binomial regression. RESULTS: The age- and sex-standardized pharmacy-dispensed naloxone rate in Ontario was 5.5 (range 1.8-11.6) kits per 1000 population. Variables associated with higher naloxone dispensing rates included opioid use disorder history [rate ratio (RR) 2.27; 95% confidence interval (CI) 1.75-2.96], opioid agonist therapy (RR 11.17; 95% CI 7.15-17.44), and PHU opioid overdose rate (RR 1.09 per 10 deaths; 95% CI 1.06-1.13). Pharmacy-dispensed naloxone rates were lower in rural areas (RR 0.83; 95% CI 0.73-0.94) and among individuals dispensed one (RR 0.72; 95% CI 0.65-0.79), two to five (RR 0.67; 95% CI 0.54-0.84) or 6-10 (RR 0.92; 95% CI 0.74-1.14) opioids in the prior year relative to those receiving no opioids. CONCLUSION: Pharmacy-dispensed naloxone programs are important components of a public health response to the opioid overdose crisis. We found considerable variation in pharmacy-dispensed naloxone rates that could limit program effectiveness, particularly in rural settings with limited access to health and harm reduction services..

Synaptic activity regulates AMPA receptor trafficking through different recycling pathways.

Changes in glutamatergic synaptic strength in brain are dependent on AMPA-type glutamate receptor (AMPAR) recycling, which is assumed to occur through a single local pathway. In this study, we present evidence that AMPAR recycling occurs through different pathways regulated by synaptic activity. Without synaptic stimulation, most AMPARs recycled in dynamin-independent endosomes containing the GTPase, Arf6. Few AMPARs recycled in dynamin-dependent endosomes labeled by transferrin receptors (TfRs). AMPAR recycling was blocked by alterations in the GTPase, TC10, which co-localized with Arf6 endosomes. TC10 mutants that reduced AMPAR recycling had no effect on increased AMPAR levels with long-term potentiation (LTP) and little effect on decreased AMPAR levels with long-term depression. However, internalized AMPAR levels in TfR-containing recycling endosomes increased after LTP, indicating increased AMPAR recycling through the dynamin-dependent pathway with synaptic plasticity. LTP-induced AMPAR endocytosis is inconsistent with local recycling as a source of increased surface receptors, suggesting AMPARs are trafficked from other sites.

SAP97 directs NMDA receptor spine targeting and synaptic plasticity.

SAP97 is a multidomain scaffold protein implicated in the forward trafficking and synaptic localization of NMDA- and AMPA-type glutamate receptors. Alternative splicing of SAP97 transcripts gives rise to palmitoylated αSAP97 and L27-domain containing ßSAP97 isoforms that differentially regulate the subsynaptic localization of GluR1 subunits of AMPA receptors. Here, we examined whether SAP97 isoforms regulate the mechanisms underlying long-term potentiation (LTP) and depression (LTD) and find that both α- and ß-forms of SAP97 impair LTP but enhance LTD via independent isoform-specific mechanisms. Live imaging of α- and ßSAP97 revealed that the altered synaptic plasticity was not due to activity-dependent changes in SAP97 localization or exchange kinetics. However, by recording from pairs of synaptically coupled hippocampal neurons, we show that αSAP97 occludes LTP by enhancing the levels of postsynaptic AMPA receptors, while ßSAP97 blocks LTP by reducing the synaptic localization of NMDA receptors. Examination of the surface pools of AMPA and NMDA receptors indicates that αSAP97 selectively regulates the synaptic pool of AMPA receptors, whereas ßSAP97 regulates the extrasynaptic pools of both AMPA and NMDA receptors. Knockdown of ßSAP97 increases the synaptic localization of both AMPA and NMDA receptors, showing that endogenous ßSAP97 restricts glutamate receptor expression at excitatory synapses. This isoform-dependent differential regulation of synaptic versus extrasynaptic pools of glutamate receptors will determine how many receptors are available for the induction and the expression of synaptic plasticity. Our data support a model wherein SAP97 isoforms can regulate the ability of synapses to undergo plasticity by controlling the surface distribution of AMPA and NMDA receptors.

Synaptic integration of newly generated neurons in rat dissociated hippocampal cultures.

In the dentate gyrus of the hippocampus new neurons are born from precursor cells throughout development and into adulthood. These newborn neurons hold significant potential for self-repair of brain damage caused by neurodegenerative disease. However, the mechanism by which newborn neurons integrate into the brain is not understood due to a lack of knowledge of the molecular and functional characteristics of the synapses formed by newborn neurons. Here we report that dissociated hippocampal cultures continue to produce new granule cells in vitro that fire action potentials and become synaptically integrated into the existing network of mature hippocampal neurons. Quantification of the expression of synaptic proteins at newborn and mature granule cell synapses revealed synapse development onto newborn neurons occurs sequentially with initial synaptic contacts evident from 6 days after cell birth. These data also showed that the dendrites of newborn neurons have a high density of Piccolo and Bassoon puncta on them and therefore have a high potential to be integrated into the neuronal network through new synaptic connections. Electrophysiological recordings from newborn neurons reveal these synapses are functional within 10 days of cell birth. GABAergic input synapses were found to mature faster in newborn neurons than glutamatergic synapses where sequential recruitment of postsynaptic glutamate receptors occurred. Group I metabotropic glutamate receptors (mGluR1/5) were present at higher levels compared with ionotropic glutamate receptors (NMDA and AMPA receptors), suggesting that metabotropic and ionotropic receptors play differential roles at glutamatergic synapses in the integration and the maturation of newborn neurons. These data show that dissociated hippocampal cultures can provide a useful model system in which to study the integration of newborn neurons into existing neuronal circuits to increase our understanding of how the function of newborn neuron synapses could contribute to restoring damaged neuronal networks.

Lithium modulates cortical excitability in vitro.

The sometimes devastating mood swings of bipolar disorder are prevented by treatment with selected antiepileptic drugs, or with lithium. Abnormal membrane ion channel expression and excitability in brain neurons likely underlie bipolar disorder, but explaining therapeutic effects in these terms has faced an unresolved paradox: the antiepileptic drugs effective in bipolar disorder reduce Na(+) entry through voltage-gated channels, but lithium freely enters neurons through them. Here we show that lithium increases the excitability of output neurons in brain slices of the mouse olfactory bulb, an archetypical cortical structure. Treatment in vitro with lithium (1 to 10mM) depolarizes mitral cells, blocks action potential hyperpolarization, and modulates their responses to synaptic input. We suggest that Na(+) entry through voltage-gated channels normally directly activates K(+) channels regulating neuron excitability, but that at therapeutic concentrations, lithium entry and accumulation reduces this K(+) channel activation. The antiepileptic drugs effective in bipolar disorder and lithium may thus share a membrane target consisting of functionally coupled Na(+) and K(+) channels that together control brain neuron excitability.