The study of dopamine dynamics in transgenic mouse models

Brain slice experiments are a robust and controlled platform for the study of neurotransmitter dynamics using electrochemistry. The isolation and study of brain slices from genetically altered animals is critical for the understanding of neurotransmitter dynamics. The dynamics of biogenic amine neurotransmitters are important for movement and addiction studies. This dissertation focuses on the use of five separate transgenic mouse models to increase the understanding of biogenic amine transmission in the brain. Fast scan cyclic voltammetry and amperometry at carbon fiber microelectrodes were used to directly monitor the dynamics of dopamine, serotonin, and norepinephrine. The amount of neurotransmitter available to act on neuronal targets is a balance of release and uptake. A transgenic mouse model lacking the presynaptic protein synapsin was used to show that dopamine has a unique presynaptic architecture making it susceptible to release facilitation by cocaine, a drug of abuse. Additionally, mice expressing different amounts of the dopamine transporter were studied to show that the dopamine transporter is a critical regulator of extracellular dopamine concentrations. The importance of mitochondrial energy output was studied in animals lacking uncoupling protein 2, a regulator of mitochondrial function and two disease state mouse models indicated a relationship between obesity and dopamine release that does not extend to mental retardation. High performance liquid chromatography was used to support the conclusions drawn from the electrochemical measurements in brain tissue. Finally, methodologies related to brain slice experimentation were evaluated to better understand how these measurements can be improved

In vivo voltammetric monitoring of norepinephrine release in the rat ventral bed nucleus of the stria terminalis and anteroventral thalamic nucleus

The role and contribution of the dense noradrenergic innervation in the ventral bed nucleus of the stria terminalis (vBNST) and anteroventral thalamic nucleus (AV) to biological function and animal behaviors is poorly understood due to the small size of these nuclei. The aim of this study was to compare norepinephrine release and uptake in the vBNST with that in the AV of anesthetized rats. Measurements were made in vivo with fast-scan cyclic voltammetry following electrical stimulation of noradrenergic projection pathways, either the dorsal noradrenergic bundle (DNB) or the ventral noradrenergic bundle (VNB). The substance detected was identified as norepinephrine based upon voltammetric, anatomical, neurochemical, and pharmacological evidence. Fast-scan cyclic voltammetry enables the selective monitoring of local norepinephrine overflow in the vBNST evoked by the stimulation of either the DNB or VNB while norepinephrine in the AV was only evoked by DNB stimulation. The α2-adrenoceptor antagonist, yohimbine, and the norepinephrine uptake inhibitor, desipramine, increased norepinephrine overflow and slowed its disappearance in both regions. However, control of extracellular norepinephrine by both autoreceptors and uptake was greater in the AV. The greater control exerted by autoreceptors and uptake in the AV resulted in reduced extracellular concentration compared to the vBNST when large numbers of stimulation pulses were employed. The differences in noradrenergic transmission observed in the terminal fields of the vBNST and the AV may differentially regulate activity in these two regions that both contain high densities of norepinephrine terminals

In vivo measurement of somatodendritic release of dopamine in the ventral tegmental area

The ventral tegmental area (VTA), the locus of mesolimbic dopamine cell bodies, contains dopamine. Experiments in brain slices have demonstrated that VTA dopamine can be released by local electrical stimulation. Measurements with both push-pull cannula and microdialysis in intact animals have also obtained evidence for releasable dopamine. Here we demonstrate that dopamine release in the VTA can be evoked by remote stimulations of the medial forebrain bundle (MFB) in the anesthetized rat. In initial experiments, the MFB was electrically stimulated while a carbon-fiber electrode was lowered to the VTA, with recording by fast-scan cyclic voltammetry. While release was not observed with the carbon fiber 4 to 6 mm below dura, a voltammetric response was observed a t 6-8 mm below dura, but the voltammogram was poorly defined. At lower depths, in the VTA, dopamine release was evoked. Immunohistochemistry experiments with antibodies for tyrosine hydroxylase (TH) confirmed that dopamine processes were primarily found below 8 mm. Similarly, tissue content determined by liquid chromatography revealed serotonin but not dopamine dorsal to 8 mm with both dopamine and serotonin at lower depths. Evaluation of the VTA signal by pharmacological means showed that it increased with inhibitors of dopamine uptake, but release was not altered by D2 agents. Dopamine release in the VTA was frequency dependent and could be exhausted by stimulations longer than 5 s. Thus, VTA dopamine release can be evoked in vivo by remote stimulations and it resembles release in terminal regions, possessing a similar uptake mechanism and a finite releasable storage pool

Optimizing the Temporal Resolution of Fast-Scan Cyclic Voltammetry

Electrochemical detection with carbon-fiber microelectrodes has become an established method to monitor directly the release of dopamine from neurons and its uptake by the dopamine transporter. With constant potential amperometry (CPA), the measured current provides a real time view of the rapid concentration changes, but the method lacks chemical identification of the monitored species and markedly increases the difficulty of signal calibration. Monitoring with fast-scan cyclic voltammetry (FSCV) allows species identification and concentration measurements but often exhibits a delayed response time due to the time-dependent adsorption/desorption of electroactive species at the electrode. We sought to improve the temporal resolution of FSCV to make it more comparable to CPA by increasing the waveform repetition rate from 10 to 60 Hz with uncoated carbon-fiber electrodes. The faster acquisition led to diminished time delays of the recordings that tracked more closely with CPA measurements. The measurements reveal that FSCV at 10 Hz underestimates the normal rate of dopamine uptake by about 18%. However, FSCV collection at 10 and 60 Hz provide identical results when a dopamine transporter (DAT) blocker such as cocaine is bath applied. To verify further the utility of this method, we used transgenic mice that overexpress DAT. After accounting for the slight adsorption delay time, FSCV at 60 Hz adequately monitored the increased uptake rate that arose from overexpression of DAT and, again, was similar to CPA results. Furthermore, the utility of collecting data at 60 Hz was verified in an anesthetized rat by using a higher scan rate (2400 V/s) to increase sensitivity and the overall signal

Neuropeptide Release Is Impaired in a Mouse Model of Fragile X Mental Retardation Syndrome

Fragile X syndrome (FXS), an inherited disorder characterized by mental retardation and autism-like behaviors, is caused by the failure to transcribe the gene for fragile X mental retardation protein (FMRP), a translational regulator and transporter of select mRNAs. FXS model mice (Fmr1 KO mice) exhibit impaired neuropeptide release. Release of biogenic amines does not differ between wild-type (WT) and Fmr1 KO mice. Rab3A, an mRNA cargo of FMRP involved in the recruitment of vesicles, is decreased by ∼50% in synaptoneurosomes of Fmr1 KO mice; however, the number of dense-core vesicles (DCVs) does not differ between WT and Fmr1 KO mice. Therefore, deficits associated with FXS may reflect this aberrant vesicle release, specifically involving docking and fusion of peptidergic DCVs, and may lead to defective maturation and maintenance of synaptic connections

FebriDx point-of-care test in patients with suspected COVID-19: a pooled diagnostic accuracy study

Background: Point-of-care (POC) tests for COVID-19 could relieve pressure on isolation resource, support infection prevention and control, and help commence more timely and appropriate treatment. We aimed to undertake a systematic review and pooled diagnostic test accuracy study of available individual patient data (IPD) to evaluate the diagnostic accuracy of a commercial POC test (FebriDx) in patients with suspected COVID-19.Methods: A literature search was performed on the 1st of October 2020 to identify studies reporting diagnostic accuracy statistics of the FebriDx POC test versus real time reverse transcriptase polymerase chain reaction (RT-PCR) testing for SARS-CoV-2. Studies were screened for risk of bias. IPD were sought from studies meeting the inclusion and exclusion criteria. Logistic regression was performed to investigate the study effect on the outcome of the RT-PCR test result in order to determine whether it was appropriate to pool results. Diagnostic accuracy statistics were calculated with 95% confidence intervals (CIs).Results: 15 studies were screened, and we included two published studies with 527 hospitalised patients. 523 patients had valid FebriDx results for Myxovirus resistance protein A (MxA), an antiviral host response protein. The FebriDx test produced a pooled sensitivity of 0.920 (95% CI: 0.875-0.950) and specificity of 0.862 (0.819-0.896) compared with RT-PCR, where there was an estimated true COVID-19 prevalence of 0.405 (0.364-0.448) and overall FebriDx test yield was 99.2%. Patients were tested at a median of 4 days [interquartile range: 2:9] after symptom onset. No differences were found in a sub-group analysis of time tested since the onset of symptoms.Conclusions: Based on a large sample of patients from two studies during the first wave of the SARS-CoV-2 pandemic, the FebriDx POC test had reasonable diagnostic accuracy in a hospital setting with high COVID-19 prevalence, out of influenza season. More research is required to determine how FebriDx would perform in other healthcare settings with higher or lower COVID-19 prevalence, different patient populations, or when other respiratory infections are in circulation

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Psilocybin-Assisted Group Therapy and Attachment: Observed Reduction in Attachment Anxiety and Influences of Attachment Insecurity on the Psilocybin Experience

Attachment insecurity is determined early in life, is a risk factor for psychopathology, and can be measured on two separate continuous dimensions: attachment anxiety and attachment avoidance. Therapeutic changes toward more secure attachment correlate with reduction in psychiatric symptoms. Psilocybin-assisted psychotherapy has demonstrated promise in the treatment of psychopathology, such as treatment-resistant depression and substance use disorders. We hypothesized that psilocybin-assisted psychotherapy would reduce attachment anxiety and attachment avoidance, thus increasing attachment security. We also hypothesized that baseline measures of attachment insecurity, which can reflect a diminished capacity for trust and exploration, would inform the quality of the psilocybin session. Participants were male long-term AIDS survivors with moderate-severe demoralization (n = 18). Using the Experiences in Close Relationships scale, we measured attachment insecurity at baseline as well as immediately, and 3 months, after completion of a brief group therapy course, which included a single midtreatment open-label psilocybin session conducted individually. Clinically important aspects of the psilocybin session were assessed using the revised Mystical Experience Questionnaire and the Challenging Experience Questionnaire the day following psilocybin administration. Self-reported ratings of attachment anxiety decreased significantly from baseline to 3-months post-intervention, t(16) = -2.2; p = 0.045; d rm = 0.45; 95% CI 0.01, 0.87. Attachment avoidance did not change significantly. Baseline attachment anxiety was strongly correlated with psilocybin-occasioned mystical-type experiences, r(15) = 0.53, p = 0.029, and baseline attachment avoidance was strongly correlated with psilocybin-related challenging experiences, r(16) = 0.62, p = 0.006. These findings have important implications for the general treatment of psychopathology as well as optimizing psilocybin-assisted psychotherapy as a broadly applicable treatment modality