Drugs for Parkinson's disease reduce tremor induced by physostigmine

Anticholinergic drugs for parkinsonism and other movement disorders

Anticholinergic (AC) drugs, a medication class that acts by blocking nicotinic and muscarinic acetylcholine receptors, were first utilized for therapeutic purposes in the mid-19th century. Initial applications were as symptomatic therapy for Parkinson disease (PD), a practice continuing to the present. Initially, the AC drugs used were naturally-occurring plant compounds. Synthetic AC drugs were developed in the late 1940s and predominated in neurological therapeutics. Until the advent of pharmaceuticals acting upon striatal dopaminergic motor pathways, AC drugs provided the only effective means for lessening tremors and other clinical problems of the PD patient. However, because dopaminergic compounds are so effective at meeting the needs of the typical PD patient, AC medications are far less utilized by clinicians today. In recent years, there has been only a few investigations of AC drugs as neurological treatments. This review will revisit the clinical landscape of AC pharmacology and application for movement disorders along with recent research in search of improving therapeutics with AC drugs.

A single exposure to the tremorgenic mycotoxin lolitrem B inhibits voluntary motor activity and spatial orientation but not spatial learning or memory in mice

The indole diterpenoid toxin lolitrem B is a tremorgenic agent found in the common grass species, perennial ryegrass (Lolium perenne). The toxin is produced by a symbiotic fungus Epichloë festucae (var. lolii) and ingestion of infested grass with sufficient toxin levels causes a movement disorder in grazing herbivores known as 'ryegrass staggers'. Beside ataxia, lolitrem B intoxicated animals frequently show indicators of cognitive dysfunction or exhibition of erratic and unpredictable behaviours during handling. Evidence from field cases in livestock and controlled feeding studies in horses have indicated that intoxication with lolitrem B may affect higher cortical or subcortical functioning. In order to define the role of lolitrem B in voluntary motor control, spatial learning and memory under controlled conditions, mice were exposed to a known dose of purified lolitrem B toxin and tremor, coordination, voluntary motor activity and spatial learning and memory assessed. Motor activity, coordination and spatial memory were compared to tremor intensity using a novel quantitative piezo-electronic tremor analysis. Peak tremor was observed as frequencies between 15 and 25Hz compared to normal movement at approximately 1.4-10Hz. A single exposure to a known tremorgenic dose of lolitrem B (2 mg/kg IP) induced measureable tremor for up to 72 h in some animals. Initially, intoxication with lolitrem B significantly decreased voluntary movement. By 25 h post exposure a return to normal voluntary movement was observed in this group, despite continuing evidence of tremor. This effect was not observed in animals exposed to the short-acting tremorgenic toxin paxilline. Lolitrem B intoxicated mice demonstrated a random search pattern and delayed latency to escape a 3 h post intoxication, however by 27 h post exposure latency to escape matched controls and mice had returned to normal searching behavior indicating normal spatial learning and memory. Together these data indicate that the tremor exhibited by lolitrem B intoxicated mice does not directly impair spatial learning and memory but that exposure does reduce voluntary motor activity in intoxicated animals. Management of acutely affected livestock suffering toxicosis should be considered in the context of their ability to spatially orientate with severe toxicity.

Pharmacological characterization of nicotine-induced tremor: Responses to anti-tremor and anti-epileptic agents

We previously showed that nicotine evoked kinetic tremor by activating the inferior olive, which is implicated in the pathogenesis of essential tremor, via α7 nicotinic acetylcholine receptors. Here, we evaluated the effects of various anti-tremor and anti-epileptic agents on nicotine-induced tremor in mice to clarify the pharmacological characteristics of nicotine tremor. Drugs effective for essential tremor, propranolol, diazepam and phenobarbital, all significantly inhibited kinetic tremor induced by an intraperitoneal (i.p.) injection of nicotine (1 mg/kg). In contrast, none of the medications for Parkinson's disease, l-DOPA, bromocriptine or trihexyphenidyl, affected the nicotine tremor. Among the anti-epileptic agents examined, valproate, carbamazepine and ethosuximide, significantly inhibited nicotine-induced tremor. In addition, a selective T-type Ca²⁺ channel blocker, TTA-A2, also suppressed the nicotine tremor. However, neither gabapentin, topiramate, zonisamide nor levetiracetam significantly affected nicotine-induced tremor. The present results show that nicotine-induced tremor resembles essential tremor not only on the neural basis, but also in terms of the pharmacological responses to anti-tremor agents, implying that nicotine-induced tremor can serve as a model for essential tremor. In addition, it is suggested that anti-epileptic agents, which have stimulant actions on the GABAergic system or blocking actions on voltage-gated Na⁺ channels and T-type Ca²⁺ channels, can alleviate essential tremor.

Stimulus conditioned to foot-shock stress reinstates alcohol-seeking behavior in an animal model of relapse

RATIONALE

Stress and conditioned responses to drug cues have been implicated as critical factors in relapse to drug use. In the animal literature, both the conditioned effects of drug-related stimuli and the unconditioned effects of foot-shock stress have been well documented to reinstate extinguished drug-seeking behavior. What has remained largely unexplored, however, is the significance of stimuli conditioned to foot-shock stress for the resumption of drug seeking. Additionally, although relapse is often the result of several risk factors acting in combination, the possibility that interactions among risk factors such as conditioned stress and drug cues may intensify drug-seeking behavior has received little experimental attention.

OBJECTIVES

The purpose of this study was to examine the individual and interactive effects of a stimulus conditioned to foot-shock stress (STRESS CS) and a stimulus conditioned to ethanol reward (EtOH CS) on the reinstatement of ethanol-seeking behavior following extinction.

METHODS

Male Wistar rats were trained to orally self-administer 10% ethanol on a fixed-ratio 3 schedule of reinforcement. The EtOH CS was established by response-contingently pairing 0.5 s illumination of a white cue light with each reinforced response. The STRESS CS was established by pairing a continuous white noise (70 dB) with intermittent foot shock (10 min; 0.5 mA; 0.5 s on; mean off period of 40 s). Ethanol dependence was induced by an ethanol vapor-inhalation procedure. After ethanol-maintained instrumental responding was extinguished by withholding ethanol and the EtOH CS, reinstatement tests were conducted.

RESULTS

Both exposure to the STRESS CS and response-contingent presentation of the EtOH CS reinstated extinguished responding at the previously active, ethanol-paired lever without further ethanol availability. When response-contingent availability of the EtOH CS was preceded by exposure to the STRESS CS, interactive effects of these stimuli on responding were observed. However, both the individual and interactive effects of the STRESS CS and the EtOH CS reached statistical significance only in rats with a history of ethanol dependence but not in ethanol-nondependent rats.

CONCLUSIONS

The results confirm that both conditioned stress and ethanol cues elicit ethanol-seeking behavior and, more importantly, that these stimuli produce interactive effects resulting in an increased ethanol-seeking response. The findings also indicate that susceptibility to ethanol seeking induced by conditioned stress and alcohol cues depends significantly on the history of prior alcohol exposure.

Time-dependent quantifiable withdrawal from ethanol in the rat: effect of method of dependence induction

The importance of temporal factors on the presence and severity of ethanol withdrawal signs in the rat was quantified using rating scale, tremor, and acoustic startle paradigms. Ethanol dependence was induced in naive male Wistar rats by liquid diet administration (n = 21) or vapor inhalation (n = 13). Subjects were analyzed for intensity and duration of physiological ethanol dependence in repeated-measures trials conducted over 72 h post-ethanol withdrawal. Indices of dependence included CNS hyperexcitability manifested as observable withdrawal signs increased acoustic startle reactivity, and tremor activity. Data analysis revealed that withdrawal signs, observed and elicited, generally reached peak intensities between 12 and 24 h postwithdrawal and were more readily observed following vapor inhalation than liquid diet administration, probably because of the higher BALs attained with the inhalation procedure. Results suggest a difference in time course observed with the different behavioral paradigms. In particular, a possible sensitization to startle stimuli was exhibited independent of both startle intensity and dependence induction method. The neural substrates governing these behavioral time course differences remain to be determined.

Ethanol withdrawal tremor does not interact with physostigmine-induced tremor in rat

Tremor in rats withdrawn from repeated ethanol administration was analyzed using an electronic device. The ethanol withdrawal tremor appeared in bursts during the first and second day of withdrawal and subsided at the third day of withdrawal. The frequency analysis showed that the mean frequency of withdrawal tremor was 6-7 Hz during the 48 hr observation period used. The frequency spectra of tremor induced by physostigmine (0.7 or 0.9 mg/kg) in control rats revealed that the tremoring frequency encompassed only a narrow peak, which temporarily decreased from 13 Hz to 11 Hz during the tremoring period. Arecoline (25 mg/kg) also induced tremor with a peak frequency at 13 Hz, but this tremor did not show any temporary decrease in peak frequency. The frequency analysis of tremor in ethanol withdrawn rats treated with physostigmine showed that the rats trembled at two frequencies, 6-7 Hz and 13 Hz. These two frequencies, each characteristic for one of the treatments, remained separate during the 48 hr observation period. As these two tremors did not interact with each other, it is suggested that these tremors are mediated by different mechanisms in the central nervous system. Thus it seems unlikely that the central muscarinic cholinergic system is involved in the genesis of tremor during ethanol withdrawal.

Harmine-, LON-954- and 5-hydroxytryptophan-induced tremors in rats withdrawn from ethanol

The tremors induced by harmine, LON-954 (N-carbamoyl-2-(2,6-dichlorophenyl)acetamidine hydrochloride) and 5-hydroxytryptophan (5-HTP) were studied in control rats and in rats withdrawn for 16-48 hrs from 6 to 9 days' ethanol administration. The frequencies and the intensities of the tremors were determined electronically. In control rats the frequency spectra of the tremors induced by harmine (20 mg/kg) and LON-954 (10 mg/kg) showed a narrow peak frequency at about 10 Hz. Atropine (1.2 mg/kg) altered neither the frequency nor the intensity of these tremors. 5-HTP (50 mg/kg) when given 3.5 hrs after iproniazid (100 mg/kg) induced tremor with peak frequencies at 6-7 Hz and 12 Hz. In ethanol-withdrawn rats treated with harmine or LON-954 the frequency analysis of tremor revealed a narrow peak frequency at about 12 Hz, which was neither the characteristic frequency of ethanol withdrawal tremor (6 Hz) nor that of harmine or LON-954 (10 Hz). The intensity of both harmine- and LON-954-induced tremor was significantly increased in ethanol-withdrawn rats. The ethanol-withdrawn rats were markedly sensitized to the effect of iproniazid+ 5-HTP, shown by deaths. The peak frequencies of this tremor were the same as those in control rats. The results suggest that harmine-induced tremor involves a dopaminergic-5-HT'ergic imbalance and the tremor induced by LON-954 a dopaminergic-cholinergic imbalance in the brain. The tremor in ethanol-withdrawn rats seems to be mediated by alterations in the activity of the cerebral 5-HT'ergic system.