Screening Methods for Anxiolytic drugs. A very useful description about screening methods and usefool tool to understand.

1. SCREENING METHODS OF ANTI
ANXIETY DRUGS
Dr. Jitendra Agrawal
Second year resident

2. Introduction
o Anxiety is an emotional state caused by the
perception of real or perceived danger that
threatens the security of an individual.
• It is a normal human adaptive response to
stressful events.
• Physiological anxiety – transient in nature
• Pathological anxiety – needs treatment

3. Physiological and Pathological
Anxiety
Normal
Pathological
• Jitter
• Panic attacks
• Stage-fright
• Obsessions, compulsions
• Nervousness
• Flashbacks, nightmares
• Worrying
• Pathological fear

4. Pathophysiology of anxiety
o Neurotransmitters like GABA, noradrenaline,
serotonin abnormalities – anxiety
o Amygdala, temporal lobe, hippocampus and
hypothalamus - involved in anxeity
o Neurochemical theories :
1. Noradrenaline theory
2. Serotonin theory
3. GABA receptor theory
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5. Noradrenaline theory
o ANS of anxious patients- hypersensitive to
stimuli.
o Locus coeruleus – activates epinephrine release
o Anxiogenics – stimulate locus coeruleus firing
o Anxiolytics- inhibits locus coeruleus firing and
decrease noradrenaline activity.

6. GABA Receptor Theory
o GABA – inhibitory neurotransmitter in brain.
o Has inhibitory and regulatory effects on serotonin,
noradrenaline and dopamine.
o GABAA receptor involved in anxiety; decreases
neuronal excitability
o Patients suffering from anxiety disorders have
less level of GABA in cortex.

7. Serotonin Theory
• Abnormalities in serotonin function i.e., release
and uptake plays role in anxiety.
• Greater serotonin activity – reduces
norepinephrine activity in locus cerulus.
• SSRIs – increases serotonin levels post
synaptically – blocks symptoms of anxiety.

8. Classification of anxiolytics
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Benzodiazepines
alprazolam, chlordiazepoxide , diazepam
Azapirones
Buspirone, Ispapirone, gepirone
SSRI
Citalopram ,Escitalopram ,Fluoxetine
Beta blockers
Propranalol
Sedative antihistaminic
Hydroxyzine

10. ANIMAL MODEL FOR ANXIETY
• Must add new insight or new dimension to the
process of human anxiety
• Should reproduce behavioural and pathological
features of anxiety
• Should allow investigation for neurobiological
mechanism that are not easily amenable to
study in man
• Permit reliable evaluation of anxiolytic drugs
as well as anxiogenic drugs

11. • All animal model of anxiety are common in
– Induced “fear” as an analogy to human
anxiety and to give them a basic construct
validity
– The degree to which they can be taken as
model of human anxiety is based upon their
response to BZD’s

12. BEHAVIOURAL MODEL
• Exteroceptive stimuli model
– Novel environment
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Open field test
Elevated plus maze
Staircase exploration
Black and white test box
Mirrored chamber
– Conditioned aversive procedures
– Conflict Procedures
• Geller seifter’s conflict test
• Vogel’s conflict test
– Escape avoidance procedure
– Social interaction test

13. • Interoceptive stimuli model
– Electrical stimulation of brain
– Pharmacological manipulation (drug discrimination
test)
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Caffine induced anxiety
Yohimbine induced anxiety
Flumazenil induced anxiety
Pentylenetetrazole induced anxiety
Amphetamine induced anxiety
Cacaine induced anxiety
– Foot shock induced agression
– Isolation induced agression

14. Open field test
• This behavioral model is base on the induction of anxiety
state – ambulation or freezing by exposing the animal to a
highly novel field environment of a high sound and light
• As a result their exploratory behavior is inhibited
• Open field apparatus consist of circular arena with high
sound and light sources
• Simple sterotypy: when animal move from one segment
to another – one ambulation score
• Complex sterotypy: when animal stands on its hind
limbs- one rearing score
• Urination
• defecation

15. Elevated Plus Maze Test
o Most widely used method; male mice used
o Anxiolytics –decrease anxiety
o increase open arm exploration time

16. o 2 open arms and 2 closed
arms of 50 ˣ 10 ˣ 40cm
dimensions
o Open roof arrangement
o Two open arms are opposite
to each other.
o Maze elevated at 50cm
height.

17. The rats weighing around 200g housed in pairs for 10 days prior
to testing; 6animals selected
for each group
Test drug administered 30min
prior to experimentation by i.p
route.
The rat is then placed in the
centre of the maze facing one of
the enclosed arms.

18.  Parameters Measured During Next 5
minutes:
o time spent in the open arms
o entries into the open arms
o time spent in the closed arms
o entries into the closed arms
o total arm entries

19.  Anxiolytic effect indicated by:
o increase in the proportion of time spent in
open arms
o increase in the proportion of entries into open
arms

20. Staircase exploration
• When introduced into a novel environment, rodents
experience a conflict between anxiety and exploratory
behavior manifested by increased vigilance and
behavioral activity
• Staircase climibing reflects exploratory or locomotor
activity
• Rearing behaviour is an index of anxiety state
• The no. of rearing and steps climbed to be recorded
for period of 5 minutes
• Decrease in rearing behaviour and increase in steps
climbed is characterisation of anxiolytic effect

21. male mice (Charles River strain)
with a weight between
18 and 24 g are used
Test drug administered 30min
prior to experimentation by s.c.
route.
The animal is placed on the floor
of the box with its back to the
staircase.(staircase is composed of five identical
steps 2.5 cm high, 10 cm wide )

22. Light – dark model
o Animals placed in 2 chambered systems, where
they can freely move between a bright and dark
compartment
o Number of crossings between the light and dark
sites is recorded.

23. o Apparatus - a dark and a
light chamber divided by a
photocell equipped zone.
o This case rests on an activity
monitor which counts total
locomotor activity.

24. male mice with a weight
between
18 and 24 g are used
Test drug administered 30min
prior to experimentation by i.p.
route.
The animal is placed in the cage

25. o No. of crossings through the partition
between the light and dark chambers compared
with total activity counts during the 10 min.
o Loco motor activity also monitored.
o Anxiolytics increase locomotor activity and
no. of crossings.

26. Mirrored chamber
• Novel stimulation evokes both exploration and
anxiety and therefore generates approach
avoidance conflict behaviour
• It is hypothesised that distortion of readily
traversed environment by a chamber of mirror
might produce aversion to entry
• Mice are exposed to the chamber of mirror
• Extended latency to enter the chamber of mirror
used as a parameter for anxiety analogy
• Anxiolytics reduce this latency in dose dependent
manner.

27. Geller seifter’s conflict test
• Conflict is produced by availability of
reinforcement with punishment
• Experimentally induced conflict by punishing
food rewarded behavior has been used to
differentiate between various psychoactive
drugs by Geller and Seifter

28. Geller seifter’s conflict test
• Male albino rats with a body weight of 300–400
g are housed individually.
• They are food deprived until the body weight is
gradually reduced by approximately 20% of
original and it is maintained at this level by
restricted food diet.
• Conditioning is carried out with a flash of light, a
single lever, a liquid dripper, and a grid-floor
connected to a shocker
• The animals are trained to lever press for the milk
reward in two distinct response-reward sections.

29. Geller seifter’s conflict test
• Anxiety or “conflict” segment (3 min)
• a dipper of milk is delivered in response to each
lever press (continuos reinforcement schedule
=CRF),
• accompanied by aversive foot-shock through the
grid floor
• Creates a conflict between milk reward and the a
painful foot shock

30. Geller seifter’s conflict test
• “nonconflict” segment (15 min)
• lever presses produce a drop of milk only at
variable intervals of time from 60 to 210 s
with an average reward of once per 2min
• No shocks are administered

31. Geller seifter’s conflict test
• Four cycles of 15 min nonshock variable
interval segments followed by a three minute
CRF-conflict period phase
• The total number of lever presses during the
conflict periods (CRF) and the non-conflict
periods (VI) are counted.
• Anxiolytic effect :An increase of lever presses
in the conflict periods

32. Vogel Lick-conflict (Vogel Punished
Drinking)
• Rats are deprived of
water for 48 hrs
• Then placed in
chamber with water
source
• sprague dawley rats
are used in this model

33. a water bottle with metal drinking tube is
fitted to the animal housing
Electric circuit is connected between
drinking tube and floor of cage.
i.p injection of drugs are given; 30min later
rats placed in cage and allowed to drink
water and shock given after 20 licks
For 3minutes next shocks are given for
every 12th lick
No. of shocks delivered in 3min noted for
each animal, no. of shocks received after
treatment noted

34. o number of accepted punishments (electric
shock) are measured during conflict period
 Anxiolytic effect :
o increase in the accepted shocks.

35. Social interaction test
• In unfamiliar and
brightly lit
environment, social
interactions are
suppressed.
• Anxiolytics –
counteract this
suppression.
• Animal used : male
sprague dawley rats.

36. Animals placed in groups of 5 each in a perspex open
topped box
1hr before test,2 rats from separate housing treated
with test compound orally
Placed in box with 60W bulb and behavior observed
for 10minutes
social interactions like sniffing, rearing,crawling over
the partner are observed
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37. Electric stimulation of brain
• Electrical stimulation of brain aversive areas, in
particular the midbrain central gray, induces
defensive reaction and/or flight behavior in
several species
• Used as an animal model of anxiety or of panic
attack.
• Most studies used intracerebral microinjections
of neurotransmitters, their agonists and
antagonists to elucidate the mechanisms of
aversive or antiaversive effects

38. Foot shock induced aggression
• GABA is involved in control and agrgressive
behaviour of animals.
• Benzodiazepines are thought to produce
anxiolytic effects by binding to a specific high
affinity site on GABA-A receptor
• So aggressive and fighting behavior has been
extended for GABAergic anxiolytic drug
screening.

39. Two mice are placed in a box with a grid floor consisting of
steel rods
A constant current of 0.6 or 0.8mA is supplied to the grid floor
is delivered for 5 s followed by 5 s. intermission for 3 min.
The total number of fights are recorded for each pair during
the 3-min period.
The fighting behaviour consists of vocalization, leaping,
running, rearing and facing each other with some attempt to
attack by hitting, biting or boxing
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40. Isolation induced aggression
o Male mice
subjected to
isolation develop
aggressive
behavior towards
other animals of
same sex.

41. Male Mice kept isolated for 6weeks &
aggressive behavior tested.
Male mice accustomed to live together
placed in cage of isolated mice for
5minutes
Isolated mice attacks intruderaggressiveness observed
Drugs given to isolated mice s.c or orally;
aggressive behavior tested at 60, 120,240
minutes (oral route)
If drug active- decrease in
aggressiveness
Attenuation of fighting reaction

42. In vitro methods
 GABAA receptor binding
 GABAB receptor binding
 Benzodiazepine receptor: [3H]-flunitrazepam
binding assay
 Serotonin (5-HTIA) receptor: binding of [3H]8-hydroxy-2-(di-n-propylamino)-tetralin ([3H]DPAT)
 Serotonin (5-HTIB) receptors in brain: binding
of [3H]5-hydroxytryptamine ([3H]5-HT)

43. conclusion
disorder and
• Anxiety disorder is a psychological and threat about
associated with stress, tension, fear
•
•
future.
The pathophysiology of anxiety disorder is not fully
understood and hence improper diagnosis leads to
increase morbidity and mortality rates.
Development of the screening methods resulted in
introduction of many new anxiolytic agents.
• In future aspects more reliable and easy models for
screening are to be developed.

44. References
• Hand book of experimental pharmacology.
S.K. kulkarni. 3 rd edition
• Drug Discovery an Evaluation:Pharmacological
Assays. H. Gerhard Vogel. 3rd edition
• Shenoy et al. Preclinical evaluation of
anxiolytic agents: an overview. Journal of
Pharmaceutical Research and Opinion.2011
;1(2):7-22.