CNS Depressants Lab # 2

Objectives To demonstrate the effect of different types of CNS depressants as : - General anaesthetics - Hypnotics المنومات - Sedatives المسكنات - tranquilizers المهدئات     To learn how to distinguish between their signs if they are given as unknown drugs.

Introduction CNS depressants are drugs that can be used to slow down brain activity or function . There are numerous CNS depressants; most act on the brain by affecting the neurotransmitter gamma-aminobutyric acid (GABA). GABA works by decreasing brain activity. CNS depressants have ability to increase GABA activity that they produce a drowsy or calming effect that is beneficial to those suffering from anxiety or sleep disorders.

General Anaesthetics They are drugs which produce reversible loss of consciousness الوعى . Mechanism of action : - They alter chloride channel opening cause hyperpolarization so they decrease firing. - They facilitate the inhibitory effects of GABA .

Stages Of Anesthesia The Target Stage Stage of analgesia: decrease feeling of pain but the patient is still conscious. Stage of excitement: delirium , respiration is irregular and the consciousness is lost but the feeling of severe pain is present. Stage of surgical anesthesia: regular respiration, relaxation of the skeletal muscles and the feeling of surgery is lost. The Target Stage

Stages Of Anesthesia IV. Stage of medullary depression: severe depression in vasomotor center in the medulla and respiratory center. Without full circulatory and respiratory support the result is death.

Classification of General Anesthetics There are two types of General Anesthetics agents: Inhaled Anesthetics Intravenous Anesthetics

A- Inhaled agents: Volatile liquid: e.g. Halothane, Isoflurane, Enflurane, Desflurane, Sevoflurane and Methoxyflurane. 2) Gas: e.g. Nitrous oxide . B- IV agents: Ultra short acting Barbiturates ( e.g. Thiopental), Ketamine, Propofol, Midazolam (Benzodiazepines) and Fentanyl ( Opioid).

Hypnotics They are drugs that induce sleep in case of insomnia. e.g. Barbiturates and Benzodiazepines. Barbiturates & Benzodiazepines act by enhance the actions of GABA.

Classification of Barbiturates Based on the duration of action Ultrashort acting: ( 15 minutes) e.g. Thiopental. Short acting: ( 2-4 hours) e.g. Pentobarbital . Intermediate acting: (4-6 hours) e.g. Amobarbital. Long acting: ( 6-8 hours): e.g. Phenobarbital.

Sedatives Drug that cause sedation and to calm the patient down without inducing sleep. When the dose increased they will induce sleep. E.g. Chloral Hydrate Trichloroethanol is the active metabolite of chloral hydrate . Trichloroacetic acid is the toxic metabolite .

Tranquilizers They are drugs which used to relieve mental anxiety and stress. E.g. chlorpromazine (CPZ). Work by blocking dopamine (D )receptor. 2

Righting reflex Test the ability of the mice to assume optimal position . When it lost: (-ve) With Phenobarbital righting reflex –ve With Chloral hydrate: at sedative dose the righting reflex is +ve , when the dose repeated it will induce sleep and the righting reflex will be –ve. With chlorpromazine: righting reflex is +ve and still +ve even the dose is repeated .

Chlorpromazine (CPZ) After injection of CPZ we can observe signs as: Ataxic gait: loss of muscle coordination . Catalepsy : rigid body Grasping test (CPZ): When you trying to put the mice on the cord, the mice will fall down

Calculate the dose Type Example Conc (g%) Dose (mg/kg) Hypnotic Phenobarbital 2% 200 Sedative Chloral Hydrate 3% 150 Tranquilizer Chlorpromazine 0.2% 40 Injection volume = Dose (mg/Kg) x Body weight in Grams Conc g% x 10000 = xxxxx ml