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

I. Stage of analgesia: decrease feeling of pain but the patient is still conscious.

II. Stage of excitement: delirium , respiration is irregular and the consciousness is lost but the feeling of severe pain is present.

III. 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:

1) Inhaled Anesthetics

2) Intravenous Anesthetics

A- Inhaled agents:

1) 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

1. Ultrashort acting: ( 15 minutes) e.g. Thiopental.

2. Short acting: ( 2-4 hours) e.g. Pentobarbital .

3. Intermediate acting: (4-6 hours) e.g. Amobarbital.

4. 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