ABSTRACT
Neuropeptide S (NPS) is a highly conserved peptide found in all tetrapods that functions in the brain to promote heightened arousal; however, the subpopulations mediating these phenomena remain unknown. We generated mice expressing Cre recombinase from the Nps gene locus (NpsCre) and examined populations of NPS+ neurons in the lateral parabrachial area (LPBA), the peri-locus coeruleus (peri-LC) region of the pons, and the dorsomedial thalamus (DMT). We performed brain-wide mapping of input and output regions of NPS+ clusters and characterized expression patterns of the NPS receptor 1 (NPSR1). While the activity of all three NPS+ subpopulations tracked with vigilance state, only NPS+ neurons of the LPBA exhibited both increased activity prior to wakefulness and decreased activity during REM sleep, similar to the behavioral phenotype observed upon NPSR1 activation. Accordingly, we found that activation of the LPBA but not the peri-LC NPS+ neurons increased wake and reduced REM sleep. Furthermore, given the extended role of the LPBA in respiration and the link between behavioral arousal and breathing rate, we demonstrated that the LPBA but not the peri-LC NPS+ neuronal activation increased respiratory rate. Together, our data suggest that NPS+ neurons of the LPBA represent an unexplored subpopulation regulating breathing, and they are sufficient to recapitulate the sleep/wake phenotypes observed with broad NPS system activation.
Subject(s)
Neuropeptides , Mice , Animals , Neuropeptides/genetics , Neuropeptides/metabolism , Arousal/physiology , Brain/physiology , Wakefulness/physiology , Sleep/physiology , Neurons/physiology , RespirationABSTRACT
Neuropeptide S (NPS) is a neuromodulatory peptide that acts via a G protein-coupled receptor. Centrally administered NPS suppresses anxiety-like behaviors in rodents while producing a paradoxical increase in arousal. In addition, NPS increases drug-seeking behavior when administered during cue-induced reinstatement. Conversely, an NPS receptor (NPSR) antagonist, RTI-118, decreases cocaine-seeking behavior. A biased NPSR ligand, RTI-263, produces anxiolytic-like effects and has memory-enhancing effects similar to those of NPS but without the increase in arousal. In the present study, we show that RTI-263 decreased cocaine seeking by both male and female rats during cue-induced reinstatement. However, RTI-263 did not modulate the animals' behaviors during natural reward paradigms, such as palatable food intake, feeding during a fasting state, and cue-induced reinstatement of sucrose seeking. Therefore, NPSR biased agonists are a potential pharmacotherapy for substance use disorder because of the combined benefits of decreased drug seeking and the suppression of anxiety.
Subject(s)
Anti-Anxiety Agents , Cocaine , Neuropeptides , Female , Rats , Male , Animals , Cocaine/pharmacology , Anti-Anxiety Agents/pharmacology , Anti-Anxiety Agents/therapeutic use , Receptors, G-Protein-Coupled , Behavior, Animal , Drug-Seeking Behavior , Neuropeptides/pharmacology , Self Administration , Cues , Extinction, PsychologicalABSTRACT
Activation of the neuropeptide S receptor (NPSR) system has been shown to produce anxiolytic-like actions, arousal, and enhance memory consolidation, whereas blockade of the NPSR has been shown to reduce relapse to substances of abuse and duration of anesthetics. We report here the discovery of a novel core scaffold (+) N-benzyl-3-(2-methylpropyl)-1-oxo-3-phenyl-1H,3H,4H,5H,6H,7H-furo[3,4-c]pyridine-5-carboxamide with potent NPSR antagonist activity in vitro. Pharmacokinetic parameters demonstrate that 14b reaches pharmacologically relevant levels in plasma and the brain following intraperitoneal (i.p.) administration, but is cleared rapidly from plasma. Compound 14b was able to block NPS (0.3 nmol)-stimulated locomotor activity in C57/Bl6 mice at 3 mg/kg (i.p.), indicating potent in vivo activity for the structural class. This suggests that 14b can serve as a useful tool for continued mapping of the pharmacological functions of the NPS receptor system.
ABSTRACT
Progressive Supranuclear Palsy (PSP) is the most common atypical parkinsonism and exhibits hallmark symptomology including motor function impairment and dysexecutive dementia. In contrast to Parkinson's disease, the underlying pathology displays aggregation of the protein tau, which is also seen in disorders such as Alzheimer's disease. Currently, there are no pharmacological treatments for PSP, and drug discovery efforts are hindered by the lack of an animal model specific to PSP. Based on previous results and clinical pathology, it was hypothesized that viral deposition of tau in cholinergic neurons within the hindbrain would produce a tauopathy along neural connections to produce PSP-like symptomology and pathology. By using a combination of ChAT-CRE rats and CRE-dependent AAV vectors, wildtype human tau (the PSP-relevant 1N4R isoform; hTau) was expressed in hindbrain cholinergic neurons. Compared to control subjects (GFP), rats with tau expression displayed deficits in a variety of behavioural paradigms: acoustic startle reflex, marble burying, horizontal ladder and hindlimb motor reflex. Postmortem, the hTau rats had significantly reduced number of cholinergic pedunculopontine tegmentum and dopaminergic substantia nigra neurons, as well as abnormal tau deposits. This preclinical model has multiple points of convergence with the clinical features of PSP, some of which distinguish between PSP and Parkinson's disease.
Subject(s)
Nervous System Diseases , Supranuclear Palsy, Progressive , Animals , Cholinergic Agents , Cholinergic Neurons/metabolism , Humans , Rats , Supranuclear Palsy, Progressive/genetics , Tegmentum Mesencephali/metabolism , tau Proteins/genetics , tau Proteins/metabolismABSTRACT
Pedunculopontine nucleus (PPN) cholinergic neurons are implicated in freezing of gait in Parkinson's disease (PD) and motor stereotypy in normal animals, but the causal role of these neurons on specific gait parameters and treatment-induced dyskinesia remains speculative. Therefore, we examined whether selective cholinergic lesion of the rostral PPN affects PD motor and gait deficits, L-DOPA-induced dyskinesia and motor improvement, and DA-agonist-induced dyskinesia. Sprague-Dawley rats were assigned to one unilaterally lesioned group: Sham lesion, PPN cholinergic lesion with diphtheria urotensin II fusion toxin, medial forebrain bundle dopamine lesion with 6-hydroxydopamine, or dual acetylcholine and dopamine lesion. We used gait analysis and forepaw adjusting steps to examine PD gait and motor deficits. Forepaw adjusting steps were also used to assess motor improvement with L-DOPA treatment. The abnormal involuntary movements scale measured L-DOPA and dopamine D1- and D2-receptor agonist-induced dyskinesia. Lesions, verified via tyrosine hydroxylase and choline acetyltransferase immunohistochemistry reduced an average of 95% of nigral dopamine neurons and 80% of PPN cholinergic neurons, respectively. Rats receiving acetylcholine and dual lesion demonstrated enhanced freezing, and acetylcholine lesioned rats exhibited increased print area and stand index. Dopamine and dual lesion produced similar forepaw adjusting steps task on and off L-DOPA. Relative to DA lesioned rats, dual lesioned rats displayed reduced L-DOPA and DA agonist-induced dyskinesia at specific time points. Our results indicate that PPN cholinergic neurons affect gait parameters related to postural stability. Therefore, therapeutically targeting PPN cholinergic neurons could reduce intractable postural instability in PD without affecting motor benefits or side effects of L-DOPA treatment.
Subject(s)
Dyskinesias , Gait Disorders, Neurologic , Parkinson Disease , Animals , Cholinergic Agents , Disease Models, Animal , Gait , Levodopa , Oxidopamine/toxicity , Rats , Rats, Sprague-DawleyABSTRACT
Cannabinoid subtype 1 receptor (CB1R) antagonists were originally developed as anti-obesity agents. Unfortunately, SR1417116A (rimonabant), the first marketed inverse agonist of CB1R, produced CNS-related adverse effects including depression and suicidal ideation, and thus it was withdrawn from the market. These effects of rimonabant became evident in patients following chronic dosing. Standard preclinical toxicity studies failed to detect these adverse effects. The goal of these studies was to perform an integrated battery of behavioral assays to better understand the behavioral effects of rimonabant following both acute and chronic administration. In the present study, acute dosing with rimonabant in rats significantly decreased food consumption; decreased measures of locomotor activity; increased scratching, grooming and wet-dog shakes; and increased defecation. Subsequently, animals were tested using a chronic dosing regimen but prior to drug administration for that day. The highest dose of rimonabant tested significantly decreased marble burying behavior, presumably anxiolysis. There were also significant effects in social interaction after chronic dosing. Our results did not reveal significant rimonabant-induced anxiogenic behaviors. Future studies to characterize behavioral screens for anxiogenic effects of CB1 antagonists in rodents should further explore social interaction paradigms and potential comorbid factors of rimonabant dosing such as sex, age, and obesity.
Subject(s)
Behavior, Animal/drug effects , Cannabinoid Receptor Antagonists/pharmacology , Locomotion/drug effects , Receptor, Cannabinoid, CB1/antagonists & inhibitors , Rimonabant/pharmacology , Social Behavior , Animals , Cannabinoid Receptor Antagonists/administration & dosage , Cannabinoid Receptor Antagonists/adverse effects , Male , Rats , Rats, Sprague-Dawley , Rimonabant/administration & dosage , Rimonabant/adverse effectsABSTRACT
The pedunculopontine tegmentum (PPTg) plays a role in processing multiple sensory inputs and innervates brain regions associated with reward-related behaviors. The urotensin II receptor, activated by the urotensin II peptide (UII), is selectively expressed by the cholinergic neurons of the PPTg. Although the exact function of cholinergic neurons of the PPTg is unknown, they are thought to contribute to the perception of reward magnitude or salience detection. We hypothesized that the activation of PPTg cholinergic neurons would alter sensory processing across multiple modalities (ex. taste and hearing). Here we had three aims: first, determine if cholinergic activation is involved in consumption behavior of palatable solutions (sucrose). Second, if so, distinguish the impact of the caloric value by using saccharin, a zero calorie sweetener. Lastly, we tested the UII-mediated effects on perception of acoustic stimuli by measuring acoustic startle reflex (ASR). Male Sprague-Dawley rats were bilaterally cannulated into the PPTg, then placed under food restriction lasting the entire consumption experiment (water ad lib.). Treatment consisted of a microinjection of either 1 µL of aCSF or 1 µL of 10 µM UII into the PPTg, and the rats were immediately given access to either sucrose or saccharin. For the remaining five days, rats were allowed one hour access per day to the same sweet solution without any further treatments. During the saccharin experiment rats were tested in a contact lickometer which recorded each individual lick to give insight into the microstructure of the consumption behavior. ASR testing consisted of a baseline (no treatment), treatment day, and two additional days (no treatment). Immediately following the microinjection of UII, consumption of both saccharin and sucrose increased compared to controls. This significant increase persisted for days after the single administration of UII, but there was no generalized arousal or increase in water consumption between testing sessions. The effects on ASR were not significant. Activating cholinergic PPTg neurons may lead to a miscalculation of the salience of external stimuli, implicating the importance of cholinergic input in modulating a variety of behaviors. The long-lasting effects seen after UII treatment support further research into the role of sensory processing on reward related-behaviors at the level of the PPTg cholinergic neurons.
Subject(s)
Feeding Behavior/drug effects , Pedunculopontine Tegmental Nucleus , Sweetening Agents/pharmacology , Urotensins/pharmacology , Acoustic Stimulation , Animals , Male , Microinjections , Parasympathetic Nervous System/drug effects , Rats , Rats, Sprague-Dawley , Reflex, Startle/drug effects , Reward , Saccharin/pharmacology , Sucrose/pharmacology , Taste/drug effects , Urotensins/administration & dosageABSTRACT
Progressive supranuclear palsy (PSP) is the most common atypical Parkinsonism. Although PSP shares some symptomology with Parkinson's disease (PD), PSP has a different underlying pathology characterized by tau aggregation. Furthermore, PSP sufferers respond poorly to PD medications and there are no effective alternative therapeutics. The development of both palliative and disease altering therapeutics has been hampered by the lack of an animal model that displays relevant PSP-like pathology and behavioral deficits. Previously, our lab found that in rats the selective removal of cholinergic pedunculopontine neurons (whose axonal projections overlap with areas of PSP pathology), mimics the extensive loss of cholinergic pedunculopontine neurons seen in PSP, and produces a unique PSP-like combination of deficits in: startle reflex, attention, and motor function. The present study extends those findings by allowing the lesion to incubate for over a year and compares behavioral and post-mortem pathology of pedunculopontine-cholinergic-lesioned and sham-lesioned rats. There was an early startle reflex deficit which did not improve over time. Progressive declines in motor function developed over the course of the year, including an increase in the number of "slips" while navigating various beams and poorly coordinated transitions from an elevated platform into homecages. Histological analysis discovered that the loss off cholinergic pedunculopontine neurons precipitated a significant loss of substantia nigra tyrosine hydroxylase-positive neurons and a significant enlargement of the lateral ventricles. The latter is a distinguishing feature between PSP and PD. This preclinical animal model of PSP has the potential to further our understanding of PSP and aid in the testing of potential therapeutic agents.
Subject(s)
Cholinergic Agents/pharmacology , Cholinergic Neurons/pathology , Motor Activity/drug effects , Supranuclear Palsy, Progressive/drug therapy , Tegmentum Mesencephali/pathology , Acetylcholine/pharmacology , Animals , Cholinergic Neurons/drug effects , Disease Models, Animal , Male , Nervous System Diseases/drug therapy , Nervous System Diseases/pathology , Rats, Long-Evans , Substantia Nigra/drug effects , Substantia Nigra/pathology , Supranuclear Palsy, Progressive/physiopathology , Tegmentum Mesencephali/drug effects , Tyrosine 3-Monooxygenase/drug effectsABSTRACT
The neuropeptide S system has been implicated in a number of centrally mediated behaviors including memory consolidation, anxiolysis, and increased locomotor activity. Characterization of these behaviors has been primarily accomplished using the endogenous 20AA peptide (NPS) that demonstrates relatively equal potency for the calcium mobilization and cAMP second messenger pathways at human and rodent NPS receptors. This study is the first to demonstrate that truncations of the NPS peptide provides small fragments that retain significant potency only at one of two single polymorphism variants known to alter NPSR function (NPSR-107I), yet demonstrate a strong level of bias for the calcium mobilization pathway over the cAMP pathway. We have also determined that the length of the truncated peptide correlates with the degree of bias for the calcium mobilization pathway. A modified tetrapeptide analog (4) has greatly attenuated hyperlocomotor stimulation in vivo but retains activity in assays that correlate with memory consolidation and anxiolytic activity. Analog 4 also has a bias for the calcium mobilization pathway, at the human and mouse receptor. This suggests that future agonist ligands for the NPS receptor having a bias for calcium mobilization over cAMP production will function as non-stimulatory anxiolytics that augment memory formation.
Subject(s)
Anti-Anxiety Agents/pharmacology , Locomotion/drug effects , Memory/drug effects , Neuropeptides/pharmacology , Receptors, G-Protein-Coupled/agonists , Receptors, G-Protein-Coupled/metabolism , Adaptation, Ocular/drug effects , Analysis of Variance , Animals , Avoidance Learning/drug effects , Calcium/metabolism , Cyclic AMP/metabolism , Dose-Response Relationship, Drug , HEK293 Cells , Humans , Male , Mice , Mice, Inbred C57BL , Mutation/genetics , Neuropeptides/chemistry , Receptors, G-Protein-Coupled/genetics , Transfection , alpha-Fetoproteins/metabolismABSTRACT
Clozapine N-oxide (CNO) is a ligand for a powerful chemogenetic system that can selectively inhibit or activate neurons; the so-called Designer Receptors Exclusively Activated by Designer Drugs (DREADD) system. This system consists of synthetic G-protein-coupled receptors, which are not believed to be activated by any endogenous ligand, but are activated by the otherwise inert CNO. However, it has previously been shown that the administration of CNO in humans and rats leads to detectable levels of the bioactive compounds clozapine and N-desmethylclozapine (N-Des). As a follow-up, experiments were conducted to investigate the effects of CNO in male Long-Evans rats. It was found that 1 mg/kg CNO reduced the acoustic startle reflex but had no effect on prepulse inhibition (PPI; a measure of sensorimotor gating). CNO (2 and 5 mg/kg) had no effect on the disruption to PPI induced by the NMDA antagonist phencyclidine or the muscarinic antagonist scopolamine. In locomotor studies, CNO alone (at 1, 2, and 5 mg/kg) had no effect on spontaneous locomotion, but 5 mg/kg CNO pretreatment significantly attenuated d-amphetamine-induced hyperlocomotion. In line with the behavioral results, fast-scan cyclic voltammetry found that 5 mg/kg CNO significantly attenuated the d-amphetamine-induced increase in evoked dopamine. However, the effects seen after CNO administration cannot be definitively ascribed to CNO because biologically relevant levels of clozapine and N-Des were found in plasma after CNO injection. Our results show that CNO has multiple dose-dependent effects in vivo and is converted to clozapine and N-Des emphasizing the need for a CNO-only DREADD-free control group when designing DREADD-based experiments.
Subject(s)
Behavior, Animal/drug effects , Central Nervous System Agents/pharmacology , Clozapine/analogs & derivatives , Amphetamine/pharmacology , Animals , Auditory Perception/drug effects , Central Nervous System Agents/blood , Clozapine/administration & dosage , Clozapine/blood , Clozapine/metabolism , Clozapine/pharmacology , Designer Drugs , Dopamine/metabolism , Dose-Response Relationship, Drug , Male , Motor Activity/drug effects , Nucleus Accumbens/drug effects , Nucleus Accumbens/metabolism , Phencyclidine/pharmacology , Rats, Long-Evans , Receptors, Muscarinic/metabolism , Receptors, Neurotransmitter/metabolism , Research Design , Scopolamine/pharmacology , Sensory Gating/drug effectsABSTRACT
Estradiol (E2) decreases both water and saline intakes by female rats. The ERα and ERß subtypes are expressed in areas of the brain that control fluid intake; however, the role that these receptors play in E2's antidipsogenic and antinatriorexigenic effects have not been examined. Accordingly, we tested the hypothesis that activation of ERα and ERß decreases water and saline intakes by female rats. We found a divergence in E2's inhibitory effect on intake: activation of ERα decreased water intake, whereas activation of ERß decreased saline intake. E2 decreases expression of the angiotensin II type 1 receptor (AT1R), a receptor with known relevance to water and salt intakes, in multiple areas of the brain where ERα and ERß are differentially expressed. Therefore, we tested for agonist-induced changes in AT1R mRNA expression by RT-PCR and protein expression by analyzing receptor binding to test the hypothesis that the divergent effects of these ER subtypes are mediated by region-specific changes in AT1R expression. Although we found no changes in AT1R mRNA or binding in areas of the brain known to control fluid intake associated with agonist treatment, the experimental results replicate and extend previous findings that body weight changes mediate alterations in AT1R expression in distinct brain regions. Together, the results reveal selective effects of ER subtypes on ingestive behaviors, advancing our understanding of E2's inhibitory role in the controls of fluid intake by female rats.
Subject(s)
Body Weight/physiology , Drinking/physiology , Estrogen Receptor alpha/physiology , Estrogen Receptor beta/physiology , Receptor, Angiotensin, Type 1/biosynthesis , Receptor, Angiotensin, Type 1/genetics , Angiotensin II/pharmacology , Animals , Body Weight/drug effects , Brain Chemistry/genetics , Drinking/drug effects , Estradiol/pharmacology , Estrogen Receptor alpha/drug effects , Estrogen Receptor beta/drug effects , Estrogens/pharmacology , Female , RNA, Messenger/biosynthesis , RNA, Messenger/genetics , Rats , Rats, Long-Evans , Receptor, Angiotensin, Type 1/drug effectsABSTRACT
Pedunculopontine nucleus (PPN) cholinergic neurons, which exert excitatory nicotinic control over substantia nigra dopaminergic neurons, degenerate in Parkinson's disease (PD). This finding and other studies showing that nicotine, the preferential agonist of nicotinic acetylcholine receptors, is neuroprotective in experimental models of PD suggest that a deficit in PPN excitatory cholinergic inputs might contribute to the death of nigral dopaminergic neurons in PD. To explore this possibility, we used lesion paradigms of dopaminergic and/or cholinergic systems in rats and monkeys. Consistent with our hypothesis, we observed that stereotaxic lesioning of PPN cholinergic neurons with diphtheria toxin coupled to urotensin II resulted in a significant loss of nigral dopaminergic neurons in rats and induced morphological changes in these neurons in macaques. Unexpectedly, a lesion of dopaminergic neurons induced by unilateral striatal injection of 6-hydroxydopamine (6-OHDA) in rats, or by repeated systemic injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in macaques, led to a 29% and 7% loss of PPN cholinergic neurons, respectively. Lastly, when the PPN cholinergic lesion was performed in rats in which the dopaminergic lesion induced by 6-OHDA was in progress, loss of cholinergic neurons was more drastic than when each neurotransmitter system was lesioned separately. Thus, our results suggest that strong PPN cholinergic and dopaminergic interactions may be an important mechanism in the pathophysiology of PD.
Subject(s)
Cholinergic Neurons/pathology , Dopaminergic Neurons/pathology , Parkinson Disease/pathology , Pedunculopontine Tegmental Nucleus/pathology , Substantia Nigra/pathology , Animals , Macaca fascicularis , Male , Oxidopamine , Rats , Rats, Sprague-DawleyABSTRACT
Protein arginine methylation regulates diverse functions of eukaryotic cells, including gene expression, the DNA damage response, and circadian rhythms. We showed that arginine residues within the third intracellular loop of the human D2 dopamine receptor, which are conserved in the DOP-3 receptor in the nematode Caenorhabditis elegans, were methylated by protein arginine methyltransferase 5 (PRMT5). By mutating these arginine residues, we further showed that their methylation enhanced the D2 receptor-mediated inhibition of cyclic adenosine monophosphate (cAMP) signaling in cultured human embryonic kidney (HEK) 293T cells. Analysis of prmt-5-deficient worms indicated that methylation promoted the dopamine-mediated modulation of chemosensory and locomotory behaviors in C. elegans through the DOP-3 receptor. In addition to delineating a previously uncharacterized means of regulating GPCR (heterotrimeric guanine nucleotide-binding protein-coupled receptor) signaling, these findings may lead to the development of a new class of pharmacological therapies that modulate GPCR signaling by changing the methylation status of these key proteins.
Subject(s)
Protein-Arginine N-Methyltransferases/metabolism , Receptors, Dopamine D2/metabolism , Amino Acid Motifs , Amino Acid Sequence , Animals , Animals, Genetically Modified , Arginine/chemistry , Caenorhabditis elegans/drug effects , Caenorhabditis elegans/genetics , Caenorhabditis elegans/metabolism , Caenorhabditis elegans Proteins/chemistry , Caenorhabditis elegans Proteins/genetics , Caenorhabditis elegans Proteins/metabolism , Computational Biology , Conserved Sequence , Dopamine/metabolism , Dopamine/pharmacology , HEK293 Cells , Humans , Locomotion/drug effects , Locomotion/genetics , Locomotion/physiology , Methylation , Molecular Sequence Data , Octanols/pharmacology , Odorants , Protein-Arginine N-Methyltransferases/deficiency , Protein-Arginine N-Methyltransferases/genetics , Receptors, Dopamine D2/chemistry , Receptors, Dopamine D2/genetics , Receptors, G-Protein-Coupled/chemistry , Receptors, G-Protein-Coupled/genetics , Receptors, G-Protein-Coupled/metabolism , Sequence Homology, Amino Acid , Signal TransductionABSTRACT
Cholinergic neurons of the pedunculopontine tegmental nucleus (PPTg) are thought to be involved in cognitive functions such as sustained attention, and lesions of these cells have been documented in patients showing fluctuations of attention such as in Parkinson's disease or dementia with Lewy Body. Animal studies have been conducted to support the role of these cells in attention, but the lesions induced in these animals were not specific to the cholinergic PPTg system, and were assessed by post-mortem methods remotely performed from the in vivo behavioral assessments. Moreover, sustained attention have not been directly assessed in these studies, but rather deduced from indirect measurements. In the present study, rats were assessed on the 5-Choice Serial Reaction Time Task (5-CSRTT), and a specific measure of variability in response latency was created. Animals were observed both before and after selective lesion of the PPTg cholinergic neurons. Brain cholinergic denervation was assessed both in vivo and ex vivo, using PET imaging with [(18)F]fluoroethoxybenzovesamicol ([(18)F]FEOBV) and immunocytochemistry respectively. Results showed that the number of correct responses and variability in response latency in the 5-CSRTT were the only behavioral measures affected following the lesions. These measures were found to correlate significantly with the number of PPTg cholinergic cells, as measured with both [(18)F]FEOBV and immunocytochemistry. This suggests the primary role of the PPTg cholinergic cells in sustained attention. It also allows to reliably use the PET imaging with [(18)F]FEOBV for the purpose of assessing the relationship between behavior and cholinergic innervation in living animals.
Subject(s)
Attention Deficit Disorder with Hyperactivity/diagnostic imaging , Cholinergic Neurons/pathology , Pedunculopontine Tegmental Nucleus/injuries , Piperidines/pharmacokinetics , Analysis of Variance , Animals , Attention Deficit Disorder with Hyperactivity/chemically induced , Autopsy , Choline O-Acetyltransferase , Cholinergic Neurons/drug effects , Disease Models, Animal , Fluorodeoxyglucose F18/pharmacokinetics , Male , Neurotoxins/toxicity , Phosphopyruvate Hydratase/metabolism , Positron-Emission Tomography , Rats , Rats, Long-Evans , Reaction Time/drug effects , Reaction Time/physiology , Statistics as Topic , Time FactorsABSTRACT
Previous studies show that the angiotensin type 1 receptor (AT1R) is susceptible to rapid desensitization, but that more chronic treatments that stimulate ANG II lead to sensitization of several responses. It is unclear, however, if the processes of desensitization and sensitization interact. To test for differences in AT1R expression associated with single or repeated injections of ANG II, we measured AT1R mRNA in nuclei that control fluid intake of rats given ANG II either in a single injection or divided into three injections spaced 20 min apart. Rats given a single injection of ANG II had more AT1R mRNA in the subfornical organ (SFO) and the periventricular tissue surrounding the anteroventral third ventricle (AV3V) than did controls. The effect was not observed, however, when the same cumulative dose of ANG II was divided into multiple injections. Behavioral tests found that single daily injections of ANG II sensitized the dipsogenic response to ANG II, but a daily regimen of four injections did not cause sensitization. Analysis of (125)I-Sar(1)-ANG II binding revealed a paradoxical decrease in binding in the caudal AV3V and dorsal median preoptic nucleus after 5 days of single daily injections of ANG II; however, this effect was absent in rats treated for 5 days with four daily ANG II injections. Taken together, these data suggest that a desensitizing treatment regimen prevents behavior- and receptor-level effects of repeated daily ANG II.
Subject(s)
Angiotensin II/administration & dosage , Behavior, Animal/drug effects , Brain/drug effects , Drinking/drug effects , Receptor, Angiotensin, Type 1/drug effects , Animals , Autoradiography , Binding Sites , Brain/metabolism , Down-Regulation , Drug Administration Schedule , Drug Tolerance , Injections, Intraventricular , Male , RNA, Messenger/metabolism , Rats, Sprague-Dawley , Receptor, Angiotensin, Type 1/genetics , Receptor, Angiotensin, Type 1/metabolism , Time FactorsABSTRACT
Sensorimotor gating is the state-dependent transfer of sensory information into a motor system. When this occurs at an early stage of the processing stream it enables stimuli to be filtered out or partially ignored, thereby reducing the demands placed on advanced systems. Prepulse inhibition (PPI) of the acoustic startle reflex (ASR) is the standard measure of sensorimotor gating. A brainstem-midbrain circuitry is widely viewed as mediating both PPI and ASR. In this circuitry, the pedunculopontine tegmental nucleus (PPTg) integrates sensory input and cortico-basal ganglia output and, via presumed cholinergic signaling, inhibits ASR-generating neurons within the reticular formation. Non-selective damage to all neuronal types within PPTg reduces PPI. We assessed whether this effect originates in the loss of cholinergic signaling by examining ASR and PPI in rats bearing non-selective (excitotoxic) or selective cholinergic (Dtx-UII) lesions of PPTg. Excitotoxic lesions had no effect on ASR but reduced PPI at all prepulse levels tested. In contrast, selective depletion of cholinergic neurons reduced ASR to the extent that PPI was not measurable with standard (10-20 s) inter-trial intervals. Subsequent testing revealed appreciable ASRs could be generated when the inter-trial interval was increased (180 s). Under these conditions, PPI was assessed and no deficits were found after lesions of cholinergic PPTg neurons. These results show that cholinergic output from PPTg is essential for rapidly regenerating the ASR, but has no influence on PPI. Results are discussed in terms of sensorimotor integration circuitry and psychiatric disorders that feature disrupted ASR and PPI.
Subject(s)
Cholinergic Neurons/physiology , Pedunculopontine Tegmental Nucleus/physiopathology , Prepulse Inhibition/physiology , Reflex, Startle/physiology , Acoustic Stimulation , Animals , Diphtheria Toxin/toxicity , Excitatory Amino Acid Agonists/toxicity , Ibotenic Acid/toxicity , Male , Rats, Sprague-Dawley , Urotensins/toxicityABSTRACT
Patients with Parkinson's disease (PD) display significant sleep disturbances and daytime sleepiness. Dopaminergic treatment dramatically improves PD motor symptoms, but its action on sleep remains controversial, suggesting a causal role of nondopaminergic lesions in these symptoms. Because the pedunculopontine nucleus (PPN) regulates sleep and arousal, and in view of the loss of its cholinergic neurons in PD, the PPN could be involved in these sleep disorders. The aims of this study were as follows: (1) to characterize sleep disorders in a monkey model of PD; (2) to investigate whether l-dopa treatment alleviates sleep disorders; and (3) to determine whether a cholinergic PPN lesion would add specific sleep alterations. To this end, long-term continuous electroencephalographic monitoring of vigilance states was performed in macaques, using an implanted miniaturized telemetry device. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment induced sleep disorders that comprised sleep episodes during daytime and sleep fragmentation and a reduction of sleep efficiency at nighttime. It also induced a reduction in time spent in rapid eye movement (REM) sleep and slow-wave sleep and an increase in muscle tone during REM and non-REM sleep episodes and in the number of awakenings and movements. l-Dopa treatment resulted in a partial but significant improvement of almost all sleep parameters. PPN lesion induced a transient decrease in REM sleep and in slow-wave sleep followed by a slight improvement of sleep quality. Our data demonstrate the efficacy of l-dopa treatment in improving sleep disorders in parkinsonian monkeys, and that adding a cholinergic PPN lesion improves sleep quality after transient sleep impairment.
Subject(s)
Levodopa/therapeutic use , MPTP Poisoning/physiopathology , Parkinsonian Disorders/physiopathology , Pedunculopontine Tegmental Nucleus/physiopathology , Sleep Disorders, Intrinsic/etiology , Animals , Benserazide/pharmacology , Benserazide/therapeutic use , Cholinergic Neurons/drug effects , Diphtheria Toxin/genetics , Diphtheria Toxin/toxicity , Drug Combinations , Levodopa/pharmacology , MPTP Poisoning/complications , MPTP Poisoning/drug therapy , Macaca fascicularis , Male , Muscle Tonus/drug effects , Muscle Tonus/physiology , Parkinsonian Disorders/complications , Parkinsonian Disorders/drug therapy , Pedunculopontine Tegmental Nucleus/injuries , Polysomnography , Recombinant Fusion Proteins/toxicity , Sleep Deprivation/drug therapy , Sleep Deprivation/etiology , Sleep Deprivation/physiopathology , Sleep Disorders, Intrinsic/drug therapy , Sleep Disorders, Intrinsic/physiopathology , Sleep, REM/drug effects , Sleep, REM/physiology , Urotensins/genetics , Wakefulness/physiologyABSTRACT
Anatomically and functionally located between basal ganglia and brainstem circuitry, the pedunculopontine tegmental nucleus (PPTg) is in a pivotal position to contribute to motor behavior. Studies in primates have reported akinesia and postural instability following destruction of the PPTg. In humans, the PPTg partially degenerates in Parkinson's disease and stimulation of this region is under investigation as a possible therapeutic. Studies in rats report no crude motor impairment following PPTg lesion, although a detailed assessment of the role of the PPTg in rat motor function has not been reported. Our studies applied motor tests generally used in rodent models of Parkinson's disease to rats bearing either excitotoxic damage to all neuronal populations within PPTg, or selective destruction of the cholinergic subpopulation created with the toxin Dtx-UII. Neither lesion type altered baseline locomotion. On the rotarod, excitotoxic lesions produced a persistent impairment on the accelerating, but not fixed speed, conditions. In the vermicelli handling task (a quantitative measure of fine motor control and effective behavioral sequencing) excitotoxic lesions produced no single impairment, but globally increased the number of normal and abnormal behaviors. In contrast, depletion of cholinergic PPTg neurons produced impairment on the accelerating rotarod but no changes in vermicelli handling. Together, these results show that while PPTg lesions produce no impairment in the execution of individual motor actions, impairments emerge when the demands of the task increase. Results are discussed in terms of PPTg acting as part of a rapid action selection system, which integrates sensory information into motor output.
Subject(s)
Cholinergic Neurons/physiology , Motor Activity/physiology , Neurons/physiology , Pedunculopontine Tegmental Nucleus/physiology , Animals , Ibotenic Acid/toxicity , Male , Pedunculopontine Tegmental Nucleus/pathology , Rats , Rats, Sprague-Dawley , Rotarod Performance TestABSTRACT
INTRODUCTION: [(18)F]fluoroethoxybenzovesamicol ([(18)F]FEOBV) is a PET radiotracer with high selectivity and specificity to the vesicular acetylcholine transporter (VAChT). It has been shown to be a sensitive in vivo measurement of changes of cholinergic innervation densities following lesion of the nucleus basalis of Meynert (NBM) in rat. The current study used [(18)F]FEOBV with PET imaging to detect the effect of a highly selective lesion of the pedunculopontine (PPTg) nucleus in rat. METHODS: After bilateral and selective lesions of the PPTg cholinergic neurons, rats were scanned using [(18)F]FEOBV, then sacrificed, and their brain tissues collected for immunostaining and quantification of the VAChT. RESULTS: Comparisons with control rats revealed that cholinergic losses can be detected in the brainstem, lateral thalamus, and pallidum by using both in vivo imaging methods with [(18)F]FEOBV, and ex vivo measurements. In the brainstem PPTg area, significant correlations were observed between in vivo and ex vivo measurements, while this was not the case in the thalamic and pallidal projection sites. CONCLUSIONS: These findings support PET imaging with [(18)F]FEOBV as a reliable in vivo method for the detection of neuronal terminal losses resulting from lesion of the PPTg. Useful applications can be found in the study of neurodegenerative diseases in human, such as Parkinson's disease, multiple system atrophy, progressive supranuclear palsy, or dementia with Lewy bodies.
Subject(s)
Cholinergic Neurons/diagnostic imaging , Pedunculopontine Tegmental Nucleus/cytology , Piperidines , Positron-Emission Tomography , Animals , Male , RatsABSTRACT
The addicted phenotype is characterized as a long-lasting, chronically relapsing disorder that persists following long periods of abstinence, suggesting that the underlying molecular changes are stable and endure for long periods even in the absence of drug. Here, we investigated Transforming Growth Factor-Beta Type I receptor (TGF-ß R1) expression in the nucleus accumbens (NAc) following periods of withdrawal from cocaine self-administration (SA) and a sensitizing regimen of non-contingent cocaine. Rats were exposed to either (i) repeated systemic injections (cocaine or saline), or (ii) self-administration (cocaine or saline) and underwent a period of forced abstinence (either 1 or 7 days of drug cessation). Withdrawal from cocaine self-administration resulted in an increase in TGF-ß R1 protein expression in the NAc compared to saline controls. This increase was specific for volitional cocaine intake as no change in expression was observed following a sensitizing regimen of experimenter-administered cocaine. These findings implicate TGF-ß signaling as a novel potential therapeutic target for treating drug addiction.