Generating Acute and Chronic Experimental Models of Motor Tic Expression in Rats

Summary

We present protocols for generating acute and chronic experimental models of tic expression in freely behaving rats. The models are based on striatal cannula implantation and subsequent GABA_A antagonist application. The acute model uses transient injections whereas the chronic model utilizes prolonged infusions via a subcutaneous implanted mini-osmotic pump.

Abstract

Motor tics are sudden, rapid, recurrent movements that are the key symptoms of Tourette syndrome and other tic disorders. The pathophysiology of tic generation is associated with abnormal inhibition of the basal ganglia, particularly its primary input structure, the striatum. In animal models of both rodents and non-human primates, local application of GABA_A antagonists, such as bicuculline and picrotoxin, into the motor parts of the striatum induces local disinhibition resulting in the expression of motor tics.

Here, we present acute and chronic models of motor tics in rats. In the acute model, bicuculline microinjections through a cannula implanted in the dorsal striatum elicit the expression of tics lasting for short time periods of up to an hour. The chronic model is an alternative enabling the extension of tic expression to periods of several days or even weeks, utilizing continuous infusion of bicuculline via a sub-cutaneous mini-osmotic pump.

The models enable the study of the behavioral and neural mechanisms of tic generation throughout the cortico-basal ganglia pathway. The models support the implantation of additional recording and stimulation devices in addition to the injection cannulas, thus allowing for a wide variety of usages such as electrical and optical stimulation and electrophysiological recordings. Each method has different advantages and shortcomings: the acute model enables the comparison of the kinematic properties of movement and the corresponding electrophysiological changes before, during and after tic expression and the effects of short-term modulators on tic expression. This acute model is simple to establish; however, it is limited to a short period of time. The chronic model, while more complex, makes feasible the study of tic dynamics and behavioral effects on tic expression over prolonged periods. Thus, the type of empirical query drives the choice between these two complementary models of tic expression.

Introduction

Tics are the defining symptom of Tourette syndrome (TS) and other tic disorders. Tics are described as sudden, rapid, recurrent movements (motor tics), or vocalizations (vocal tics)¹. Tic expression typically fluctuates in its temporal (frequency)² and spatial (intensity, body location)³ properties over multiple time scales (hours, days, months, and years). These changes are affected by different factors, such as environmental features^4,5, behavioral states^6,7, and voluntary and te....

Protocol

All procedures were approved and supervised by the Institutional Animal Care and Use Committee and adhered to the National Institutes of Health Guide for the Care and Use of Laboratory Animals and the Bar-Ilan University Guidelines for the Use and Care of Laboratory Animals in Research. This protocol was approved by the National Committee for Experiments in Laboratory Animals at the Ministry of Health.

NOTE: This protocol utilizes female Long-Evans rats (acute and chronic models) and female Sprague Dawley rats (acute model) aged 3-10 months, 280-350 g. The implementation of these models in other strains, weights or ages should be tested car....

Results

Protocols for generating the acute and chronic models for tic induction in rats were presented above. The protocols cover the full preparation for surgery and experiments (Figure 1 for the acute model, Figure 2 for the chronic model). The application of bicuculline into the motor areas of the striatum results in the expression of ongoing motor tics. Tics appear on the contralateral side to the application and are characterized by brief and repetitive muscle cont.......

Discussion

In this manuscript, we detailed the protocols of the acute and chronic models for tic induction in a freely behaving rat. These protocols describe the preparation of all components, the surgery and the experimental process which can be adapted for customization to meet specific research needs. The primary principle underlying these models is the direct local application of bicuculline to the motor areas of the striatum, which is known to play a key role in the pathophysiology of tic disorders¹⁰

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Anchor screws	Micro Fasteners	SMPPS0002	#0 x 1/8 - Pan Head Sheet Metal Screws
Bicuculline methiodide	Sigma Aldrich	14343
Cyanoacrylate (CA) accelerator	Zap	PT29
Cyanoacrylate (CA) glue	BSI	IC-2000	This glue was found to be stronger than others
Dental cement	Coltene	H00322	Hygenic Perm Repair Material Reline Resin Self Cure
Glue gel	Loctite		Ultra Gel Control
Hemostat	WPI	501242	Any hemostat sized approximately 14 cm would be sufficient
Hypo-tube, extra-thin wall 25G	Component supply company	HTX-25X
Hypo-tube, regular wall 22G	Component supply company	HTX-22R
Hypo-tube, regular wall 30G	Component supply company	HTX-30R
Infusion pump machine	New Era Pump Systems	NE-1000
Mini-osmotic pump	ALZET	2001	1.0µl per hour, 7 days
PE compatible adhesive	CEYS		Special difficult plastics (suitable for PE)
PE-10 Catheter Tubing	ALZET	PE-10	ID = 0.28mm, OD = 0.61mm
Precision glass microsyringe, 10µl	Hamilton	80065	1701 RNR 10µl syr (22s/51/3)
Tissue adhesive	3M	1469Sb	Vetbond
Tubing-adapter	CMA	3409500
Tygon micro bore tubing, 0.02 inch ID * 0.06 OD	Component supply company	TND80-020
Wire 0.005-inch	Component supply company	GWX-0050
Wire 0.013-inch	Component supply company	GWX-0130