Here is an essay on ‘Neuropharmacology’ for class 11 and 12. Find paragraphs, long and short essays on ‘Neuropharmacology’ especially written for school and college students.
Essay on Neuropharmacology
Essay # 1. Introduction to Neuropharmacology:
Neuropharmacology is that branch of health sciences which is concerned with the study of drugs affecting the nervous system. Neuropsychopharmacology is the study of drugs used for the treatment of neurological as well as psychiatric diseases. Measurement of alterations in the behavioural pattern is the central component in the field of Neuropsychopharmacology.
Scientists assume that the emotions experienced by animals are similar to those experienced by humans because of similar physiological changes that animals and human undergo. Based on this assumption it is believed that we can learn more about humans by observing animal behaviour and physiology. The entire concept of an animal model is based on this assumption.
Selection of Animals for Neupropharmacological Studies:
Selection of animals for evaluation of Neuropharmacological studies is of paramount importance. In general the animals selected for the animal model in Neuropharmacological studies should exhibit normal behaviour. These animals should not show signs of abnormal behaviour such as excessive jumping, biting, sniffing, licking, lacrimation and salivation. The animals showing such behaviour should be excluded from the study. The selected animals should be randomly distributed in age and sex.
Neuropharmacological agents can exhibit either stimulant or depressant actions. A battery of tests is needed to screen these agents. The screening should always be initiated with the effects on gross behaviour.
Essay # 2. Gross Behavioural Effects in Mice or Rats:
The test drug is administered orally or parentally as intended in therapeutics to different animal groups in graded doses. The dose selected should be the minimum expected therapeutic dose, intermediate dose (3 times higher than the therapeutic dose) and maximum expected therapeutic dose (10 times higher than the therapeutic dose).
After the drug administration to different groups of animals they are observed by the naked eye for:
1. CNS stimulant effects as evidenced by excessive jumping, biting, sniffing and scratching etc. CNS depressant effects as evidenced by excessive reduced spontaneous motor activity, sleepiness or passiveness.
2. Other effects can also be observed such as autonomic effects as evidenced by changes in papillary size, lacrimation, salivation, defecation, and urination.
At the end of 24 h all groups should be checked for mortality if any. LD50 can also be determined if possible.
Essay # 3. Behavioural Test in Golden Hamsters/Mice:
This test is used to assess efficacy of drug on gross behavioural patterns. Golden hamsters of average weight of 60 g or albino mice (35-45 g) are crowded in cages for at least 2 weeks. During this time animals develop a characteristic fighting behaviour. From these animals, one animal is placed in a glass jar of 2 litres. In this situation the animal assumes a squatting position while resting during the day.
If the animal is touched with a stick or forceps, it will arouse immediately from its resting position. If one tries to hold the hamster with a blunt forceps, a characteristic behaviour—the hamster throws itself on its back and tries to bite or push the forceps away with its legs and utters angry shrieks—is elicited.
Stimulus can be applied every 20 min. for 3 h. Only animals responding with all three defense reactions (turning, vocalising and biting) are included in the test. Suppression of defense reactions in a test group can be compared with that in the control group.
Essay # 4. Spontaneous Motor Activity in Rats:
Spontaneous motor activity is normal in rodents—it is very high especially in the dark. Any drug that produces sedation will reduce this spontaneous motor activity. Rats, which are randomly divided in control and study groups, are pre-treated with either vehicle or drug and are placed in a digital photoactometer.
A digital photoactometer is made like a box and is provided with 12-16 photocells, which can detect the spontaneous activity of rodents. After one min. acclimatisation of the activity of the animals i.e., the number of rounds the animal completes within the chamber are recorded and compared among groups.
Alterations in other gross behavioural pattern such as jumping, biting, blinking, licking, lacrimation and salivation can also be compared among groups. Rota-rod apparatus can also be used for neuro-skeletal muscular and motor activities of drugs.
Essay # 5. Open Field Behaviour:
This test is also performed to assess the effect of drugs on gross behavioural patterns. The rats or mice are placed in a large circular enclosure 85 cm in diameter with white sun mica floor. The enclosure is divided into 25 segments by the intersection of 3 concentric circles with the lines radiating from the centre. Two types of stimuli are presented to the animals: a bright light of 165 foot candles produced by 5 photographic lamps and a noise of 78 dB emanating from an oscillator and a loudspeaker.
The behavioural response is noted by using scores of ambulation (number of floor segments entered by the animal) and rearing (number of times the animal stood on its hind limbs) frequencies, immobility time (times when there is lack of movement), defecation and urination. The test is based on the assumption that effects dissipate with experience.
Therefore, two types of animals are employed: one group consisting of animals with no prior experience to the open field and another group with prior experience. The animals of the latter group are given 10 trials in open field, 2 per day at least 6 h apart for 5 days before being tested on day 6 with drugs. Plus maze and Y maze can be used for evaluating the gross behaviour as well as anxidytic activities of drugs.
Essay # 6. Sodium Barbitone Induced Hypnosis:
This test is done to evaluate the sedative and hypnotic effect of drugs. Albino mice are randomly divided into control and test groups and are pre-treated with the test vehicle or drug respectively. 1 h later pentobarbitone sodium (35 mg/kg/i.p.) is administered. The mice start to fall asleep in 15 min.
As soon as they are asleep they are gently put on their backs. Recovery from sleeps allows them to correct their posture. The time is noted when they fall asleep and noted again when they spontaneously correct their posture. The difference between the two is taken as sleeping time. Sleeping time can be compared among groups and with control.
Essay # 7. Effect on Body Temperature:
Normal rectal temperature of selected animals is recorded. Animals are then divided into groups and the desired dose of the drug is administered to one of the group while the other group is treated as for control. The rectal temperature is then recorded at hourly intervals for 4 h and then 24 h after the drug administration. The change in rectal temperature can be compared among groups. Drugs like chlorpromazine and reserpine are known to cause hypothermia because of their central depressant effects.
Essay # 8. Inhibition of Amphetamine Stereotypy in Rats:
Amphetamine, which is a sympathomimetic drug and releases catecholamines from neuronal storage pools induces a characteristic stereotypic behaviour (lip smacking, grooming, catalepsy, gnawing) in rats. This behaviour can be prevented by neuroleptic drags. This test demonstrates efficacy of anti-psychotic drags with dopamine D2 receptor antagonism.
Wistar/Sprague-Dawley rats (120-200 g) are injected with amphetamine (10 mg/kg/s.c or 5 mg/kg/i.p) 30 min. after pre-treatment with vehicle or test drag. Animals are then placed individually in stainless steel cages (40 cm × 20 cm × 18 cm). The stereotypic behaviour is evaluated at 30 min. interval for 3 h and alterations in test group are compared with control group.
Essay # 9. Conditioned Avoidance Reflex in Rats (The Pole Climbing Test):
This test was developed by Pavlov. It evaluates effects on learning and memory. Rodents are trained to avoid a noxious stimulus (electric stimuli) in response to a cue (light or sound buzzer). The anti-psychotic drugs decrease the number of conditioned avoidance responses (CAR) and prolong the total waiting time (TWT).
CNS depressants affect both avoidance and escape i.e., the animal does not try to avoid the noxious stimuli and does not escape when stimulus is applied. Anti-psychotics in low doses affect only avoidance tactics with no effect on the ability to escape whereas in high doses both are affected due to ataxia and hypnosis.
Adult healthy rats (250-300 g) are housed in a controlled environment with 22 ± 2°C temperature, 12 h light/dark cycle and free access to food and water. Rats are then trained for a period of 8 days with 10 trials each day (inter-trial period – 30 s), which lasts for 5 min.
By these trials, rats learn to climb the pole during 3 s of light conditional stimulus before an electric stimulus (2 mA) of 3 s duration is applied in the pole climbing apparatus. At the end of the training period, the animals which fail to learn pole climbing in response to light stimulus are excluded from the study.
The test is done after pre-treatment on the 9th day by giving 3 s light stimulus followed by 3 s electric stimulus (2.5 mA). Parameters evaluated include CAR and TWT. Haloperidol (0.2 mg/kg/i.p) and clozapine (10 mg/kg/i.p) are used as standard drugs.
Essay # 10. Forced Swim Test:
This test is designed for testing the behavioural despair in animals. Animals are forced to swim individually for 15 min. in a glass cylinder containing fresh water at a temperature 25 ± 2°C to avoid variations and to maintain consistency in the immobility time between different groups. This constitutes the pre-test session. 24 h later, the animals are treated with the drug or the vehicle and each animal is again forced to swim in a similar environment for a period of 6 min. The duration of immobility is recorded.
In this experimental paradigm, after a phase of vigorous swimming, the animals show an immobile floating posture. This immobility is postulated to represent a depressant-like state and is reduced or eliminated by clinically effective anti-depressant drugs. Animals are judged to be immobile if they seize struggling and remain floating motionless in water making only the necessary movements to keep their head above water.