Excessive sucrose consumption reduces synaptic density and increases cannabinoid receptors in Göttingen minipigs.

Diets high in sucrose and fat are becoming more prevalent the world over, accompanied by a raised prevalence of cardiovascular diseases, cancers, diabetes, obesity, and metabolic syndrome. Clinical studies link unhealthy diets with the development of mental health disorders, particularly depression. Here, we investigate the effects of 12 days of sucrose consumption administered as 2 L of 25% sucrose solution daily for 12 days in Göttingen minipigs on the function of brain receptors involved in reward and motivation, regulating feeding, and pre- and post-synaptic mechanisms. Through quantitative autoradiography of cryostat sections containing limbic brain regions, we investigated the effects of sucrose restricted to a 1-h period each morning, on the specific binding of [3H]raclopride on dopamine D2/3 receptors, [3H]UCB-J at synaptic vesicle glycoprotein 2A (SV2A), [3H]MPEPγ at metabotropic glutamate receptor subtype 5 (mGluR5) and [3H]SR141716A at the cannabinoid receptor 1 (CB1). Compared to control diet animals, the sucrose group showed significantly lower [3H]UCB-J and [3H]MPEPγ binding in the prefrontal cortex. The sucrose-consuming minipigs showed higher hippocampal CB1 binding, but unaltered dopamine D2/3 binding compared to the control group. We found that the sucrose diet reduced the synaptic density marker while increasing CB1 binding in limbic brain structures, which may subserve maladaptive changes in appetite regulation and feeding. Further studies of the effects of diets and lifestyle habits on brain neuroreceptor and synaptic density markers are warranted.

Subanesthetic S-ketamine does not acutely alter striatal dopamine transporter binding in healthy Sprague Dawley female rats.

Major depressive disorder is one of the most prevalent mental health disorders, posing a global socioeconomic burden. Conventional antidepressant treatments have a slow onset of action, and 30% of patients show no clinically significant treatment response. The recently approved fast-acting antidepressant S-ketamine, an N-methyl-D-aspartate receptor antagonist, provides a new approach for treatment-resistant patients. However, knowledge of S-ketamine's mechanism of action is still being established. Depressed human subjects have lower striatal dopamine transporter (DAT) availability compared to healthy controls. Rodent studies report increased striatal dopamine concentration in response to acute ketamine administration. In vivo [18F]FE-PE2I ([18F]-(E)-N-(3-iodoprop-2-enyl)-2ß-carbofluoroethoxy-3ß-(4'-methyl-phenyl) nortropane) positron emission tomography (PET) imaging of the DAT has not previously been applied to assess the effect of acute subanesthetic S-ketamine administration on DAT availability. We applied translational in vivo [18F]FE-PE2I PET imaging of the DAT in healthy female rats to evaluate whether an acute subanesthetic intraperitoneal dose of 15 mg/kg S-ketamine alters DAT availability. We also performed [3H]GBR-12935 autoradiography on postmortem brain sections. We found no effect of acute S-ketamine administration on striatal DAT binding using [18F]FE-PE2I PET or [3H]GBR-12935 autoradiography. This negative result does not support the hypothesis that DAT changes are associated with S-ketamine's rapid antidepressant effects, but additional studies are warranted.

A single dose of cocaine raises SV2A density in hippocampus of adolescent rats.

OBJECTIVE: Cocaine is a highly addictive psychostimulant that affects synaptic activity with structural and functional adaptations of neurons. The transmembrane synaptic vesicle glycoprotein 2A (SV2A) of pre-synaptic vesicles is commonly used to measure synaptic density, as a novel approach to the detection of synaptic changes. We do not know if a single dose of cocaine suffices to affect pre-synaptic SV2A density, especially during adolescence when synapses undergo intense maturation. Here, we explored potential changes of pre-synaptic SV2A density in target brain areas associated with the cocaine-induced boost of dopaminergic neurotransmission, specifically testing if the effects would last after the return of dopamine levels to baseline. METHODS: We administered cocaine (20 mg/kg i.p.) or saline to rats in early adolescence, tested their activity levels and removed the brains 1 hour and 7 days after injection. To evaluate immediate and lasting effects, we did autoradiography with [3H]UCB-J, a specific tracer for SV2A, in medial prefrontal cortex, striatum, nucleus accumbens, amygdala, and dorsal and ventral areas of hippocampus. We also measured the striatal binding of [3H]GBR-12935 to test cocaine's occupancy of the dopamine transporter at both times of study. RESULTS: We found a significant increase of [3H]UCB-J binding in the dorsal and ventral sections of hippocampus 7 days after the cocaine administration compared to saline-injected rats, but no differences 1 hour after the injection. The [3H]GBR-12935 binding remained unchanged at both times. CONCLUSION: Cocaine provoked lasting changes of hippocampal synaptic SV2A density after a single exposure during adolescence.

Synaptic Vesicle Glycoprotein 2A: Features and Functions.

In recent years, the field of neuroimaging dramatically moved forward by means of the expeditious development of specific radioligands of novel targets. Among these targets, the synaptic vesicle glycoprotein 2A (SV2A) is a transmembrane protein of synaptic vesicles, present in all synaptic terminals, irrespective of neurotransmitter content. It is involved in key functions of neurons, focused on the regulation of neurotransmitter release. The ubiquitous expression in gray matter regions of the brain is the basis of its candidacy as a marker of synaptic density. Following the development of molecules derived from the structure of the anti-epileptic drug levetiracetam, which selectively binds to SV2A, several radiolabeled markers have been synthetized to allow the study of SV2A distribution with positron emission tomography (PET). These radioligands permit the evaluation of in vivo changes of SV2A distribution held to be a potential measure of synaptic density in physiological and pathological conditions. The use of SV2A as a biomarker of synaptic density raises important questions. Despite numerous studies over the last decades, the biological function and the expressional properties of SV2A remain poorly understood. Some functions of SV2A were claimed, but have not been fully elucidated. While the expression of SV2A is ubiquitous, stronger associations between SV2A and Υ amino butyric acid (GABA)-ergic rather than glutamatergic synapses were observed in some brain structures. A further issue is the unclear interaction between SV2A and its tracers, which reflects a need to clarify what really is detected with neuroimaging tools. Here, we summarize the current knowledge of the SV2A protein and we discuss uncertain aspects of SV2A biology and physiology. As SV2A expression is ubiquitous, but likely more strongly related to a certain type of neurotransmission in particular circumstances, a more extensive knowledge of the protein would greatly facilitate the analysis and interpretation of neuroimaging results by allowing the evaluation not only of an increase or decrease of the protein level, but also of the type of neurotransmission involved.

Validation and optimisation of an automatic blood sampler for preclinical positron emission tomography research in domestic pigs.

In preclinical positron emission tomography animal studies, continuous blood sampling is used to measure the time course of the activity concentration in arterial blood. However, pigs have hypercoagulable blood that tends to clot inside plastic tubes. We tested several tube materials and lengths and the use of three-way connectors. We validated set-ups for automated blood sampling with and without blood recirculation that could run for 90 minutes without problematic clots and without any evidence of emboli formation during necropsy.

Preclinical PET Studies of [11C]UCB-J Binding in Minipig Brain.

PURPOSE: Loss of neuronal synapse function is associated with a number of brain disorders. The [11C]UCB-J positron emission tomography (PET) tracer allows for in vivo examination of synaptic density, as it binds to synaptic vesicle glycoprotein 2A (SV2A) expressed in presynaptic terminals. Here, we characterise [11C]UCB-J imaging in Göttingen minipigs. PROCEDURES: Using PET imaging, we examined tracer specificity and compared kinetic models. We explored the use of a standard blood curve and centrum semiovale white matter as a reference region. We compared in vivo [11C]UCB-J PET imaging to in vitro autoradiography, Western blotting and real-time quantitative polymerase chain reaction. RESULTS: The uptake kinetics of [11C]UCB-J could be described using a 1-tissue compartment model and blocking of SV2A availability with levetiracetam showed dose-dependent specific binding. Population-based blood curves resulted in reliable [11C]UCB-J binding estimates, while it was not possible to use centrum semiovale white matter as a non-specific reference region. Brain [11C]UCB-J PET signals correlated well with [3H]UCB-J autoradiography and SV2A protein levels. CONCLUSIONS: [11C]UCB-J PET is a valid in vivo marker of synaptic density in the minipig brain, with binding values close to those reported for humans. Minipig models of disease could be valuable for investigating the efficacy of putative neuroprotective agents for preserving synaptic function in future non-invasive, longitudinal studies.