Goran Lacan

Recovery of striatal dopamine function after acute amphetamine- and methamphetamine-induced neurotoxicity in the vervet monkey

In six vervet monkeys, presynaptic striatal dopamine function was assessed longitudinally by [18F]fluoro-L-DOPA (FDOPA)-positron emission tomography (PET) after administration (2 x 2 mg/kg, i.m., 4 h apart) of either amphetamine (Amp), n = 3, or methamphetamine (MeAmp), n = 3. At 1-2 weeks postdrug, both Amp and MeAmp exposure effected similar decreases (60-70%) in the FDOPA influx rate constant (FDOPA Ki), an index of striatal dopamine synthesis capacity. Subsequent studies in these subjects showed that FDOPA Ki values were decreased by 45-67% at 3-6 weeks, by 25% at 10-12 weeks and by 16% in one Amp-treated subject at 32 weeks. Biochemical analysis showed that striatal dopamine concentrations were decreased by 75% at 3-4 weeks and by 55% at 10-12 weeks. These results indicate that in vervet monkey striatum, an acute Amp or MeAmp drug dosage produces extensive striatal dopamine system neurotoxicity. However, these effects were reversible; observed time-dependent recovery in both FDOPA Ki and dopamine concentrations indicates that neurochemical plasticity remains active in the adult primate striatum. At 3-4 and 10-12 weeks postdrug, the concurrent characterization of the striatal FDOPA Ki and dopamine concentrations for individual subjects showed that Ki decreases between 24 and 67% corresponded to dopamine depletions of 55-85%. These relatively larger postdrug decrements in steady-state striatal dopamine concentrations suggest that compensatory increases in dopamine synthesis capacity develop in the partially lesioned striatum. In contrast to the dopamine depletion in striatum, substantia nigra concentrations remained unchanged from referent values at both 3-4 and 10-12 weeks postdrug. Thus, the integrity of the substantia nigra could not be inferred from decreases in the striatal FDOPA Ki parameter. This disparity between striatum and substantia nigra reactivity to systemic administration of amphetamines suggests that each has unique dopamine system regulatory mechanisms.

Recovery from methamphetamine induced long-term nigrostriatal dopaminergic deficits without substantia nigra cell loss

After administration of methamphetamine (METH) (2x2 mg/kg, 6 h apart) to vervet monkeys, long term but reversible dopaminergic deficits were observed in both in vivo and post-mortem studies. Longitudinal studies using positron emission tomography (PET) with the dopamine transporter (DAT)-binding ligand, [11C]WIN 35,428 (WIN), were used to show decreases in striatal WIN binding of 80% at 1 week and only 10% at 1.5 years. A post-mortem characterization of other METH subjects at 1 month showed extensive decreases in immunoreactivity (IR) profiles of tyrosine hydroxylase (TH), DAT and vesicular monoamine transporter-2 (VMAT) in the striatum, medial forebrain bundle and the ventral midbrain dopamine (VMD) cell region. These IR deficits were not associated with a loss of VMD cell number when assessed at 1.5 years by stereological methods. Further, at 1.5 years, IR profiles of METH subjects throughout the nigrostriatal dopamine system appeared similar to controls although some regional deficits persisted. Collectively, the magnitude and extent of the dopaminergic deficits, and the subsequent recovery were not suggestive of extensive axonal degeneration followed by regeneration. Alternatively, this apparent reversibility of the METH-induced neuroadaptations may be related primarily to long-term decreases in expression of VMD-related proteins that recover over time.

Development and evaluation of an automated atlas-based image analysis method for microPET studies of the rat brain

An automated method for placement of 3D rat brain atlas-derived volumes of interest (VOIs) onto PET studies has been designed and evaluated. VOIs representing major structures of the rat brain were defined on a set of digitized cryosectioned images of the rat brain. For VOI placement, each PET study was registered with a synthetic PET target constructed from the VOI template. Registration was accomplished with an automated algorithm that maximized the mutual information content of the image volumes. The accuracy and precision of this method for VOI placement was determined using datasets from PET studies of the striatal dopamine and hippocampal serotonin systems. Each evaluated PET study could be registered to at least one synthetic PET target without obvious failure. Registration was critically dependent upon the initial position of the PET study relative to the synthetic PET target, but not dependent on the amount of synthetic PET target smoothing. An evaluation algorithm showed that resultant radioactivity concentration measurements of selected brain structures had errors=2% due to misalignment with the corresponding VOI. Further, radioligand binding values calculated from these measurements were found to be more precise than those calculated from measurements obtained with manually drawn regions of interest (ROIs). Overall, evaluation results demonstrated that this atlas-derived VOI method can be used to obtain unbiased measurements of radioactivity concentration from PET studies. Its automated features, and applicability to different radioligands and brain regions, will facilitate quantitative rat brain PET assessment procedures.

Mitochondrial Dysfunction, Oxidative Stress, and Apoptosis Revealed by Proteomic and Transcriptomic Analyses of the Striata in Two Mouse Models of Parkinson’s Disease

The molecular mechanisms underlying the changes in the nigrostriatal pathway in Parkinsons disease (PD) are not completely understood. Here, we use mass spectrometry and microarrays to study the proteomic and transcriptomic changes in the striatum of two mouse models of PD, induced by the distinct neurotoxins 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and methamphetamine (METH). Proteomic analyses resulted in the identification and relative quantification of 912 proteins with two or more unique peptides and 86 proteins with significant abundance changes following neurotoxin treatment. Similarly, microarray analyses revealed 181 genes with significant changes in mRNA, following neurotoxin treatment. The combined protein and gene list provides a clearer picture of the potential mechanisms underlying neurodegeneration observed in PD. Functional analysis of this combined list revealed a number of significant categories, including mitochondrial dysfunction, oxidative stress response, and apoptosis. These results constitute one of the largest descriptive data sets integrating protein and transcript changes for these neurotoxin models with many similar end point phenotypes but distinct mechanisms.

Brain Mediation of Anolis Social Dominance Displays

Serotonin (5-HT) functions are associated with social dominance status in diverse species, but to date the brain regions wherein 5-HT exerts such effects are uncertain. Here, we indexed 5-HT turnover in male Anolis carolinensis as the ratio of 5-HT to its metabolite, 5-hydroxy-indol-acetic acid, and also as the accumulation of the in vivo tracer 14C-alpha-methyl-tryptophan (14C-AMT). After patching one eye, displaying dominant animals increased both measures of 5-HT turnover in the forebrain hemisphere receiving display-evocative visual stimuli, compared to control, contralateral brain, whereas both 5-HT turnover indices were decreased when animals displayed submissively. In contrast, various non-displaying controls showed forebrain symmetry on both measures. Drugs that stimulate 5-HT2C receptors in mammals, and have 5-HT2C-like binding in A. carolinensis, evoked some elements of dominant display behaviors in non-dominant anole males and also activated dorsolateral basal ganglia as seen in non-medicated dominants when they display [Baxter et al., 2001]. Thus, acute changes in forebrain 5-HT output from baseline equilibrium, acting at 5-HT2C-like receptors, might effect some elements of the dominant vs. submissive male anoles’ territorial displays. A mechanistic model of how this might occur is offered. Given similarities in 5-HT systems, forebrain functions, and territorial display routines, similar mechanisms might have similar functions in other amniotes, including primates.

Long-Term Methamphetamine Administration in the Vervet Monkey Models Aspects of a Human Exposure: Brain Neurotoxicity and Behavioral Profiles

Methamphetamine (METH)-associated alterations in the human striatal dopamine (DA) system have been identified with positron emission tomography (PET) imaging and post-mortem studies but have not been well correlated with behavioral changes or cumulative METH intake. Animal studies that model some aspects of human long-term METH abuse can establish dose-dependency profiles of both behavioral changes and potential brain neurotoxicities for identifying consequences of particular cumulative exposures. Based on parameters from human and our monkey pharmacokinetic studies, we modeled a prevalent human METH exposure of daily multiple doses in socially housed vervet monkeys. METH doses were escalated over 33 weeks, with final dosages resulting in estimated peak plasma METH concentrations of 1–3 μM, a range measured in human abusers. With larger METH doses, progressive increases in abnormal behavior and decreases in social behavior were observed on ‘injection’ days. Anxiety increased on ‘no injection’ days while aggression decreased throughout the study. Thereafter, during 3 weeks abstinence, differences in baseline vs post-METH behaviors were not observed. Post-mortem analysis of METH brains showed 20% lower striatal DA content while autoradiography studies of precommissural striatum showed 35% lower [3H]WIN35428 binding to the DA transporter. No statistically significant changes were detected for [3H]dihydrotetrabenazine binding to the vesicular monoamine transporter (METH-lower by 10%) or for [3H]SCH 23390 and [3H]raclopride binding to DA D1 and D2 receptors, respectively. Collectively, this long-term, escalating dose METH exposure modeling a human abuse pattern, not associated with high-dose binges, resulted in dose-dependent behavioral effects and caused persistent changes in presynaptic striatal DA system integrity.

Modulation of food intake following deep brain stimulation of the ventromedial hypothalamus in the vervet monkey: Laboratory investigation

OBJECT Deep brain stimulation (DBS) has become an effective therapy for an increasing number of brain disorders. Recently demonstrated DBS of the posterior hypothalamus as a safe treatment for chronic intractable cluster headaches has drawn attention to this target, which is involved in the regulation of diverse autonomic functions and feeding behavior through complex integrative mechanisms. In this study, the authors assessed the feasibility of ventromedial hypothalamus (VMH) DBS in freely moving vervet monkeys to modulate food intake as a model for the potential treatment of eating disorders. METHODS Deep brain stimulation electrodes were bilaterally implanted into the VMH of 2 adult male vervet monkeys by using the stereotactic techniques utilized in DBS in humans. Stimulators were implanted subcutaneously on the upper back, allowing ready access to program stimulation parameters while the animal remained conscious and freely moving. In anesthetized animals, intraoperatively and 6-10 weeks postsurgery, VMH DBS parameters were selected according to minimal cardiovascular and autonomic nervous system responses. Thereafter, conscious animals were subjected to 2 cycles of VMH DBS for periods of 8 and 3 days, and food intake and behavior were monitored. Animals were then killed for histological verification of probe placement. RESULTS During VMH DBS, total food consumption increased. The 3-month bilateral implant of electrodes and subsequent periods of high-frequency VMH stimulation did not result in significant adverse behavioral effects. CONCLUSIONS This is the first study in which techniques of hypothalamic DBS in humans have been applied in freely moving nonhuman primates. Future studies can now be conducted to determine whether VMH DBS can change hypothalamic responsivity to endocrine signals associated with adiposity for long-term modulation of food intake.

Long‐term methamphetamine‐induced decreases of [11C]WIN 35,428 binding in striatum are reduced by GDNF: PET studies in the vervet monkey

The effects of glial cell line‐derived neurotrophic factor (GDNF) pretreatment on methamphetamine (METH)‐induced striatal dopamine system deficits in the vervet monkey were characterized with [11C]WIN 35,428 (WIN)‐positron emission tomography (PET). WIN, a cocaine analog that binds to the dopamine transporter (DAT), was used to provide an index of striatal dopamine terminal integrity. In two subjects, GDNF (200 μg/40 μl) was injected into the caudate and putamen unilaterally vs. saline contralaterally. After 1–2 weeks, + and –GDNF striatal WIN‐PET binding values were equivalent as calculated by multiple time graphic analysis, suggestive of an absence of unilateral DAT up‐regulation. Three other subjects (n = 3) received GDNF injections into the caudate and putamen unilaterally and one week later, were administered METH HCl (2 × 2 mg/kg; i.m., 24 hours apart; a neurotoxic dosage for this species). At 1 week post‐METH, WIN‐PET studies showed that mean WIN binding was decreased by 72% in the +GDNF and by 92% in the –GDNF striatum relative to pre‐drug assessment values. Thus, GDNF pretreatment reduced the extent of METH‐induced decreases in WIN binding. Subsequent WIN‐PET studies (1.5–9‐month range) showed a protracted recovery of WIN binding in each striatum, indicative of long‐term but partially reversible METH neurotoxicity. Further, at each time point, WIN binding remained relatively higher in the +GDNF vs. –GDNF striatum. These results provide further evidence that the adult non‐human primate brain remains responsive to exogenously administered GDNF and that this pharmacotherapy approach can counteract aspects of neurotoxic actions associated with methamphetamine. Synapse 35:243–249, 2000.

[18F]p-MPPF: A Radiolabeled Antagonist for the Study of 5-HT1A Receptors with PET

Abstract This paper summarizes the present status of the researches conducted with [ 18 F]4-(2′-methoxyphenyl)-1-[2′-[ N -(2′′-pyridinyl)- p -fluorobenzamido]ethyl]-piperazine known as [ 18 F] p -MPPF, a new 5-HT 1A antagonist for the study of the serotonergic neurotransmission with positron emission tomography (PET). This includes chemistry, radiochemistry, animal data (rats, cats, and monkeys) with autoradiography and PET, human data with PET, toxicity, and metabolism.

Hypothalamic Deep Brain Stimulation Reduces Weight Gain in an Obesity-Animal Model

Prior studies of appetite regulatory networks, primarily in rodents, have established that targeted electrical stimulation of ventromedial hypothalamus (VMH) can alter food intake patterns and metabolic homeostasis. Consideration of this method for weight modulation in humans with severe overeating disorders and morbid obesity can be further advanced by modeling procedures and assessing endpoints that can provide preclinical data on efficacy and safety. In this study we adapted human deep brain stimulation (DBS) stereotactic methods and instrumentation to demonstrate in a large animal model the modulation of weight gain with VMH-DBS. Female Göttingen minipigs were used because of their dietary habits, physiologic characteristics, and brain structures that resemble those of primates. Further, these animals become obese on extra-feeding regimens. DBS electrodes were first bilaterally implanted into the VMH of the animals (n = 8) which were then maintained on a restricted food regimen for 1 mo following the surgery. The daily amount of food was then doubled for the next 2 mo in all animals to produce obesity associated with extra calorie intake, with half of the animals (n = 4) concurrently receiving continuous low frequency (50 Hz) VMH-DBS. Adverse motoric or behavioral effects were not observed subsequent to the surgical procedure or during the DBS period. Throughout this 2 mo DBS period, all animals consumed the doubled amount of daily food. However, the animals that had received VMH-DBS showed a cumulative weight gain (6.1±0.4 kg; mean ± SEM) that was lower than the nonstimulated VMH-DBS animals (9.4±1.3 kg; p<0.05), suggestive of a DBS-associated increase in metabolic rate. These results in a porcine obesity model demonstrate the efficacy and behavioral safety of a low frequency VMH-DBS application as a potential clinical strategy for modulation of body weight.