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Preclinical screening methods of cns stimulants

This document describes various preclinical screening methods used to evaluate central nervous system (CNS) stimulants. It discusses behavioral manifestations of CNS stimulation like increased alertness. Various screening methods are described including the actophotometer test to measure locomotor activity, strychnine-induced convulsion test, sand displacement test, runway test and others. Each test is briefly explained along with its purpose, procedure, and evaluation method. A variety of behavioral tests in animals are used to screen for CNS stimulant activity of novel compounds.

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PRECLINICAL SCREENING METHODS OF CNS STIMULANTS PRESENTED BY: RASHMI M.PHARM.1ST SEM PHARMACOLOGY
CNS STIMULANTS • CNS stimulants are the psychoactive drugs that induce temporary improvement in either mental or physical function or both. • CNS stimulants may be defined as “Drug substance that most specifically afford an enhancement in excitability either very much within the different portions of the brain or the spinal cord which may lead to convulsion.”
BEHAVIORAL MANIFESTATIONS OF CNS STIMULATION • Analeptic Effect : mild elevation in alertness, decrease in drowsiness , lessening of fatigue • Increased nervousness and anxiety -convulsions.
MOLECULAR BASIS OF CNS STIMULATION Imbalance between inhibitory and excitatory processes as in the brain. This hyper-excitability of neurons results from: • potentiation or enhancement of excitatory neurotransmission(e.g. amphetamine) • depression or antagonism of inhibitory transmission (e.g. Strychnine) • Altered presynaptic control of neurotransmitter release (e.g. picrotoxin)
CLASSIFICATION OF CNS STIMULANTS 1.Convulsant: Strychnine, Picrotoxin, Bicuculline, Pentylenetetrazol 2.Analeptics ( respiratory stimulants): Doxapram 3. Psychostimulants: Amphetamines, Methylphenidate, Atomoxetine, Modafinil, Armodafinil, Cocaine, Caffeine.  psychostimulants increase sympathetic nervous system activity.
EVALUATION METHODS • 1. Screening of analeptics by Actophotometer • 2. Strychnine induced convulsion • 3. Sand displacement method • 4. Runway test • 5. Ptosis test • 6. Duration of anaesthesia • 7. Jiggle cage method • 8. Treadwheel method • 9. Rotarod method • 10. Barbiturate induced sleeping time • 11.Hole board test • 12. open field test
SCREENING OF ANALEPTICS BY ACTOPHOTOMETER • Purpose : CNS stimulants like Amphetamine increase the locomotor activity in animal. • Principle: When the beam of light falling on the photo cell is cut off by the animal, a count is recorded. • Procedure : Mice weighing 20-25 gm are divided in in to 3 groups, each contain 4 animals. Control : Saline, Standard : Amphetamine (1 mg/kg I.P.), Test : Drug to be evaluated. Mice from each group, separately placed in actophotometer for 10 min duration at the intervals of 30 min till the maximum effect of drug is observed • Evaluation : No. of “ cut off ” is compared between groups.
STRYCHNINE INDUCED CONVULSION • Purpose : Drugs like strychnine produce convulsion and hyperreflexia by inhibiting glycine in CNS. • Procedure : Groups of 10 mice of either sex with a weight between 18 and 22 gm mice Injected with 2 mg/kg strychnine nitrate (i.p.) in std group and in test group test drug is given. After few minutes convulsions are observed. • Evaluation : Time required to produce convulsion is compared. • Modifications : Some other drugs produce same effects like Picrotoxin, Pentylenetetrazol Bicuculine.
SAND DISPLACEMENT METHOD • Purpose : Drug like Caffeine stimulate the motor activity in animal by inhibiting the adenosine transmission in the brain. • Procedure : A cage with sand is calibrated for amount of sand displaced per unit time. Mice weighing 20-25 gm are divided in 3 groups Control : saline Standard : caffeine (20 mg/kg orally) Test : drug to be evaluated. After 1 hour the animal is placed in cage for 15 min. • Evaluation : Volume of sand displaced in each group is compared.
RUNWAY TEST • Purpose : To study the spontaneous activity of CNS stimulants • Principle : The Y-shaped Runway is covered with paper that can indicate the foot prints of mice which is counted afterwards for evaluation • Procedure : Wistar rats of either sex weighing 250-300 gm are grouped ,trained to run at runway apparatus for 3 days to achieve constant time and speed to pass runway. Control : Saline, Standard : Methamphetamine (2 mg/kg I.P.), Test : Drug to be test. After 30 min of administration of drug test is performed • Evaluation : The no. of foot prints on the maze path is measured. Higher no.:CNS Stimulant Lower no.: CNS Depressant
RUNWAY APPARATUS
PTOSIS TEST • Purpose : Reserpine decreases central sympathetic outflow and leads to ptosis in eye. • Procedure : Albino mice of either sex weighing 18-24 gm are grouped. Reserpine is given in all group (4 mg/kg I.P.) ,After 2 hr 45 min Control : saline Standard : Amphetamine (1 mg/kg I.P.) Test : drug to be evaluated After 15 min ptotic rating is made. • Evaluation : 4 for complete ptosis 3 for ¾ ptosis 2 for ½ ptosis 1 for ¼ ptosis.
DURATION OF ANAESTHESIA • Purpose : Analeptics produces diminution in duration of anesthesia & also produces respiration stimulation • Procedure : rats weighing 250-350 gm are grouped . Given Pentobarbital sodium (50 mg/kg I.P.) After 20 min, Control : Saline Standard : Methamphetamine (2 mg/kg I.P.) Test : Drug to be evaluated After this, animal are placed on its back and recovery from anesthesia is checked when animal had righted itself 3 times in 1 min. • Evaluation : Recovery time from anesthesia is compared. • Modifications :Guinea pig, Rabbit, Mice, Monkey, Cat.
JIGGLE CAGE METHOD • Purpose : Test is used to evaluate the effect of drug on motor activity of animal. • Procedure : Wistar rats of either sex weighing 250-300 gm are grouped. Control : Saline Standard : Methamphetamine (2 mg/kg I.P.) Test : Drug to be evaluated. Animal are placed in jiggle cage for 10 min to observe activity changes. • Evaluation : Changes in the movement of animal. • Modification : Rat can also be used.
TREAD WHEEL METHOD • Purpose : Effect of drug on locomotor activity of rat. • Procedure : Wistar rats of either sex weighing 250-300 gm are grouped. Control : Saline Standard : Methamphetamine (2 mg/kg I.P.) Test : Drug to be evaluated. Animal placed in tread wheel for 10 min to observe activity changes. • Evaluation : Changes in the movement (speed of rotation) of animal. • Modification : Rat can also be used.
ROTA ROAD TEST • Purpose : To evaluate the effect of drug on motor coordination • Procedure : Mice weighing 18-24 gm are grouped. Control : saline Standard : Amphetamine (4 mg/kg I.P.) Test : drug to be evaluated. After 30 min Animal placed on rotarod. • Evaluation :The time for falling of animal is recorded
BARBITURATE INDUCED SLEEPING TIME • Purpose : To evaluate the effect of drug on motor coordination. • Procedure : Mice weighing 20-30 gm are grouped. Control : Distilled water (10 ml/kg I.P) Standard : caffeine (20 mg/kg S.C) Test : drug to be evaluated After 30 min Pentobarbitone (40 mg/kg I.P.). Animal are observed for onset and duration of sleeping. • Evaluation :The sleeping time( The sleeping time is the time interval between onset of loss of righting reflex and regain of righting reflex).
HOLE-BOARD TEST • Purpose: The evaluation of behavior of mice such as curiosity or exploration. • Principle: An open field with holes on the bottom is used into which the animals could poke their noses which is a sign of Curiosity. • Procedure: The hole-board has a size of 40 × 40 cm with Sixteen holes having diameter of 3cm each are distributed evenly on the floor. Mice of either sex with a weight between 18 and 22 g are used. Control: Saline Test: Drug to be evaluated. Mice are placed on the Hole-Board and Observed.
CONT. • Evaluation: The number of counts for nose-poking of treated animals is calculated To that of control animals. • Higher Curiosity • Lesser Curiosity
OPEN FIELD TEST • Purpose : To test anxiety, exploration, and locomotion in Animal. • Principle: Interruption of light beams as a measure of movements of rats or mice in an Open field. • Procedure: Open field Arena with 2-Rows of 8-Photosensitive cells placed 40mm and and 125 mm above the floor, respectively is Constructed. Adult male Sprague-Dawley rats with a weight between 280 and 320 g are used. control: saline Test: Drug to be Evaluated. Animals Placed in Centre Of Arena and Observed.
CONT. • Evaluation: a) Motor activity: All interruptions of photo beams in the lower rows. • b) Rearing: All interruption of the photo beams in the upper rows. • Higher interruption : CNS Stimulant Lower Interruption : CNS Depressant.
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