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East African Scholars Journal of Medical Sciences
Abbreviated Key Title: East African Scholars J Med Sci
ISSN 2617-4421 (Print) | ISSN 2617-7188 (Online) |
Published By East African Scholars Publisher, Kenya
Volume-2 | Issue-10| Oct -2019 |
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Article History
Received: 24.09.2019
Accepted: 05.10.2019
Published: 19.10.2019
Published By East African Scholars Publisher, Kenya 580
Review Article
Anxiety: Insights into Signs, Symptoms, Etiology, Pathophysiology, and
Treatment
Almokhtar A. Adwas1, J.M. Jbireal2 and Azab Elsayed Azab2*
1Department of Pharmacology, Faculty of Medicine, Sabratha University, Libya
2Physiology Department, Faculty of Medicine, Sabratha University, Libya
*Corresponding Author
Azab Elsayed Azab
Abstract: Background: The anxiety disorders are the most common mental disorders. It is manifest by disturbances of
mood, as well as of thinking, behaviour, and physiological activity. It includes panic disorder, agoraphobia, generalized
anxiety disorder, specific phobia, social phobia, obsessive-compulsive disorder, acute stress disorder, and post-traumatic
stress disorder. Objectives: The aim of the current review is a high light on the anxiety signs, symptoms, etiology,
pathophysiology, treatment. The common symptoms of anxiety are accompanying disturbances of sleep, concentration,
social and/or occupational functioning. The anxiety is associated with restlessness, feeling keyed up or on edge, being
easily fatigued, difficulty in concentrating or mind going blank, irritability, muscle tension, and irritability. The etiology
of anxiety may include stress, physical condition, genetic, and environmental factors. Anxiety symptoms may be due to
disrupted modulation within the central nervous system. Many believe that low serotonin system activity and elevated
noradrenergic system activity are responsible for its development. Therefore, selective serotonin reuptake inhibitors and
serotonin-norepinephrine reuptake inhibitors that is the first-line agent for its treatment. Corticosteroids may increase or
decrease the activity of certain neural pathways, affecting not only behavior under stress, but also the brain's processing
of fear-inducing stimuli. Several studies have found elevated WBC count among anxious individuals there was a
negative association between red blood cell and mean corpuscular hemoglobin and symptoms of anxiety. A positive
association between anxiety symptoms and levels of hematological inflammatory markers including WBC and RDW.
Drugs to reduce anxiety have been used by human beings for thousands of years. Conclusion: It can be concluded that
anxiety is manifest by disturbances of mood, thinking, behaviour, and physiological activity and accompanying
disturbances of sleep, concentration, social and/or occupational functioning. Also, it is associated with restlessness,
feeling keyed up or on edge, being easily fatigued, difficulty in concentrating or mind going blank, irritability, muscle
tension, and irritability. The etiology of anxiety may include stress, diabetes, depression, genetic, and environmental
factors. Anxiety disorders should be treated with psychological therapy, pharmacotherapy, or a combination of both.
Keywords: Anxiety, Signs, Symptoms, Etiology, Pathophysiology, Treatment.
1. INTRODUCTION
The anxiety disorders are the most common, or
frequently occurring, mental disorders (Munir et al.,
2019). They encompass a group of conditions that share
extreme or pathological anxiety as the principal
disturbance of mood or emotional tone. Anxiety, which
may be understood as the pathological counterpart of
normal fear, is manifest by disturbances of mood, as
well as of thinking, behaviour, and physiological
activity. The anxiety disorders include panic disorder
(with and without a history of agoraphobia),
agoraphobia (with and without a history of panic
disorder), generalized anxiety disorder, specific phobia,
social phobia, obsessive-compulsive disorder, acute
stress disorder, and post-traumatic stress disorder. In
addition, there are adjustment disorders with anxiety
features, and disorders due to general medical
conditions and substance-induced anxiety disorders
(Greenberg et al., 1999).
Diagnostic criteria are include excessive
anxiety and worry for at least six months, difficulty
controlling the worrying. The anxiety is associated with
three or more of the following symptoms for at least 6
Almokhtar A. Adwas et al., East African Scholars J Med Sci; Vol-2, Iss-10 (Oct, 2019): 580-591
© East African Scholars Publisher, Kenya 581
months: restlessness, feeling keyed up or on edge, being
easily fatigued, difficulty in concentrating or mind
going blank, irritability, muscle tension, sleep
disturbance, and irritability (Munir et al., 2019).
2. Signs and Symptoms
A subjective experience of distress with
accompanying disturbances of sleep, concentration,
social and/or occupational functioning are common
symptoms in many of the anxiety disorders. Despite
their similarities, these disorders often differ in
presentation, course and treatment. Patients often
present with complaints of poor physical health as their
primary concern. This may temporarily distract from
the underlying anxiety symptoms. This is particularly
common in panic disorder, which is characterized by a
short period of intense fear and a sense of impending,
doom, with accompanying physical symptoms, such as
chest pain, dizziness and shortness of breath
(Markowitz et al., 1989). When complicated by
agoraphobia, the individual fears have a panic attack in
a place that prevents escape. This results in the patient
avoiding such situations, with subsequent disturbances
in functioning (Magee et al., 1996). The ancient term
agoraphobia is translated from Greek as fear of an open
marketplace. Agoraphobia today describes severe and
pervasive anxiety about being in situations from which
escape might be difficult or avoidance of situations such
as being alone outside of the home, traveling in a car,
bus, or airplane, or being in a crowded area (Magee et
al., 1996).
Most people who present to mental health
specialists develop agoraphobia after the onset of panic
disorder. Agoraphobia is best understood as an adverse
behavioral outcome of repeated panic attacks and the
subsequent worry, preoccupation, and avoidance
(Barlow, 1988).
Generalized anxiety disorder (GAD) rarely
occurs without a co-morbid psychiatric disorder, with
the patient experiencing consistent worry over multiple
areas of his or her life for at least 6 months (Schweizer,
1995 ).
Social phobia describes fear and anxiety in
social situations leading to avoidance of social
interaction (Ballenger et al., 1998). Specific phobia is
characterized by similar symptoms and behavior, but is
triggered by a specific object or situation, such as a fear
of certain animals (especially snakes, rodents, and
dogs); birds, insects (especially spiders and bees or
hornets); heights; elevators; flying; automobile driving;
water; storms; and blood or injections (Marks, 1969).
Post-traumatic stress disorder and acute stress
disorder occur after a patient experiences a traumatic
event with subsequent physiological arousal in the face
of stimuli that trigger memories of the event; avoidance
of such stimuli; and a sense of re-experiencing the
event. The latter occurs in the short term, while the
former describe a more chronic version of the disorder
(Kessler et al., 1995).
Obsessive-compulsive disorder (OCD) is
characterized by repeated behaviors (compulsions),
which serve to reduce anxiety connected to unwanted,
intrusive thoughts (obsessions). Commonly seen
behaviors are cleaning or washing in response to
concerns about contamination, or repeatedly checking
to see if a stove is turned off in response to concerns
over a fire starting. Some people repeatedly check work
or seek excessive reassurance due to obsessive self-
doubt (Eddy and Walbroehl, 1998).
2. Etiology and psychological basis of anxiety
The etiology of anxiety may include stress,
physical condition such as diabetes or other co-
morbidities such as depression, genetic, first-degree
relatives with generalized anxiety disorder (25%),
environmental factors, such as child abuse, and
substance abuse (Munir et al., 2019). The anxiety
disorders are so heterogeneous that the relative roles of
these factors are likely to differ. Some anxiety
disorders, like panic disorder, appear to have a stronger
genetic basis than others (National Institute of Mental
Health [NIMH], 1998), although actual genes have not
been identified. Other anxiety disorders are more rooted
in stressful life events.
It is not clear why females have higher rates
than males of most anxiety disorders, although some
theories have suggested a role for the gonadal steroids.
Other research on women‘s responses to stress also
suggests that women experience a wider range of life
events as stressful as compared with men who react to a
more limited range of stressful events, specifically those
affecting themselves or close family members
(Maciejewski et al., 2001).
What the myriad of anxiety disorders have in
common is a state of increased arousal or fear. Anxiety
disorders often are conceptualized as an abnormal or
exaggerated version of arousal. Much is known about
arousal because of decades of study in animals and
humans of the so-called ―fight-or-flight response,‖
which also is referred to as the acute stress response.
The acute stress response is critical to understanding the
normal response to stressors and has galvanized
research, but its limitations for understanding anxiety
have come to the forefront in recent years (Barbee,
1998).
In common parlance, the term ―stress‖ refers
either to the external stressor, which can be physical or
psychosocial in nature, as well as to the internal
response to the stressor. Yet researchers distinguish the
two, calling the stressor the stimulus and the body‘s
reaction the stress response. This is an important
distinction because in many anxiety states there is no
Almokhtar A. Adwas et al., East African Scholars J Med Sci; Vol-2, Iss-10 (Oct, 2019): 580-591
© East African Scholars Publisher, Kenya 582
immediate external stressor. The following paragraphs
describe the biology of the acute stress response, as well
as its limitations, in understanding human anxiety.
Emerging views about the neurobiology of anxiety,
attempt to integrate and understand psychosocial views
of anxiety and behavior in relation to the structure and
function of the central and peripheral nervous system.
There are several major psychological theories
of anxiety: psychoanalytic and psychodynamic theory,
behavioral theories, and cognitive theories (Thorn et al.,
1999). Psychodynamic theories have focused on
symptoms as an expression of underlying conflicts
(Rush et al., 1998; Thorn et al., 1999). Although there
are no empirical studies to support these
psychodynamic theories, they are amenable to scientific
study (Kandel, 1999) and some therapists find them
useful. For example, ritualistic compulsive behavior can
be viewed as a result of a specific defense mechanism
that serves to channel psychic energy away from
conflicted or forbidden impulses. Phobic behaviors
similarly have been viewed as a result of the defense
mechanism of displacement. From the psychodynamic
perspective, anxiety usually reflects more basic,
unresolved conflicts in intimate relationships or
expression of anger.
More recent behavioral theories have
emphasized the importance of two types of learning:
classical conditioning and vicarious or observational
learning. These theories have some empirical evidence
to support them. In classical conditioning, a neutral
stimulus acquires the ability to elicit a fear response
after repeated pairings with a frightening
(unconditioned) stimulus. In vicarious learning, fearful
behavior is acquired by observing others‘ reactions to
fear-inducing stimuli (Thorn et al., 1999). With general
anxiety disorder, unpredictable positive and negative
reinforcement is seen as leading to anxiety, especially
because the person is unsure about whether avoidance
behaviors are effective.
Cognitive factors, especially the way people
interpret or think about stressful events, play a critical
role in the etiology of anxiety (Barlow et al., 1996;
Thorn et al., 1999). A decisive factor is the individual‘s
perception, which can intensify or dampen the response.
One of the most salient negative cognitions in anxiety is
the sense of uncontrollability. It is typified by a state of
helplessness due to a perceived inability to predict,
control, or obtain desired results (Barlow et al., 1996).
Negative cognitions are frequently found in individuals
with anxiety (Ingram et al., 1998). Many modern
psychological models of anxiety incorporate the role of
individual vulnerability, which includes both genetic
(Smoller & Tsuang, 1998) and acquired (Coplan et al.,
1997) predispositions. There is evidence that women
may ruminate more about distressing life events
compared with men, suggesting that a cognitive risk
factor may predispose them to higher rates of anxiety
and depression (Nolen-hoeksema et al., 1999 ).
4. Pathophysiology
The exact mechanism is not entirely known.
Anxiety can be a normal phenomenon in children.
Stranger anxiety begins at seven to nine months of life
(Munir et al., 2019). Anxiety symptoms and the
resulting disorders are thought to be due to disrupted
modulation within the central nervous system. Physical
and emotional manifestations of this dysregulation are
the result of heightened sympathetic arousal of varying
degrees (Kaplan and Sadock, 1995).
Several neurotransmitter systems have been
implicated to have a role in one or several of the
modulatory steps involved. The most commonly
considered are the serotonergic and noradrenergic
neurotransmitter systems. In very general terms, it is
thought that an under activation of the serotonergic
system and an over activation of the noradrenergic
system are involved (Ressler and Nemeroff, 2000,
Munir et al., 2019). These systems regulate and are
regulated by other pathways and neuronal circuits in
various regions of the brain, resulting in dysregulation
of physiological arousal and the emotional experience
of this arousal (Ressler and Nemeroff, 2000). Many
believe that low serotonin system activity and elevated
noradrenergic system activity are responsible for its
development. It is, therefore, selective serotonin
reuptake inhibitors (SSRI) and serotonin-
norepinephrine reuptake inhibitors (SNRI) that are the
first-line agent for its treatment (Munir et al.,
2019). Disruption of the gamma-aminobutyric acid
(GABA) system has also been implicated because of the
response of many of the anxiety spectrum disorders to
treatment with benzodiazepines (Nutt, 2001). There has
been some interest in the role of corticosteroid
regulation and its relationship to symptoms of fear and
anxiety. Corticosteroids may increase or decrease the
activity of certain neural pathways, affecting not only
behavior under stress, but also the brain's processing of
fear-inducing stimuli (Korte, 2001). Cholecystokinin
has long been viewed as a neurotransmitter involved in
regulating emotional states (Korte, 2001).
There is such careful orchestration between
these neurotransmitters that changes in one
neurotransmitter system invariably elicit changes in
another, including extensive feedback mechanisms.
Serotonin and GABA are inhibitory neurotransmitters
that quieten the stress response (Coplan and Lydiard,
1998; Rush et al., 1998). All of these neurotransmitters
have become important targets for therapeutic agents.
Many studies indicate that a genetic
predisposition to developing an anxiety disorder is
likely. However, environmental stressors clearly play a
role, in varying degrees. All of the disorders are
affected in some way by external cues and how they are
processed and reacted to (Kaplan and Sadock, 1995).
Almokhtar A. Adwas et al., East African Scholars J Med Sci; Vol-2, Iss-10 (Oct, 2019): 580-591
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Several studies have found elevated WBC
count among depressed and anxious individuals
(Pitsavos et al., 2006; Kobrosly and van Wijngaarden,
2010; Duivis et al., 2013; Aydin et al., 2016; Shafiee et
al., 2017). Shafiee et al., 2017 reported that the mean
WBC count increased with increasing severity of
symptoms of depression and anxiety among men. Men
(but not women) with severe anxiety symptoms had
significantly higher values of RDW (p <0.001).
Moreover, there was a negative association between red
blood cell (RBC) and mean corpuscular hemoglobin
(MCH) and symptoms of depression/anxiety. Pitsavos
et al. (2006) observed that anxiety score is positively
correlated with WBC count in women, but not in men.
Since WBC count is an independent predictor of
atherosclerosis and cardiovascular diseases (Loimaala
et al., 2006; Madjid et al., 2004, Shafiee et al., 2017).
RDW is a strong predictor of mortality and has
association with a variety of cardiovascular and
thrombotic disorders (Montagnana et al., 2012; Patel et
al., 2009, Shafiee et al., 2017). Therefore, higher levels
of RDW among depressed and anxious individuals may
predict greater risk of developing cardiovascular
diseases in these patients (Shafiee et al., 2017).
Shafiee et al., 2017 concluded that a positive
association between depression/anxiety symptoms and
levels of hematological inflammatory markers including
WBC and RDW, which persisted despite adjustment by
potential confounders.
5. Biochemical Basis of Anxiety
An exciting new line of research proposes that
anxiety engages a wide range of neurocircuits. This line
of research catapults to prominence two key regulatory
centers found in the cerebral hemispheres of the brain—
the hippocampus and the amygdala. These centers, in
turn, are thought to activate the hypothalamic-pituitary-
adrenocortical (HPA) axis (Goddard & Charney, 1997;
Coplan & Lydiard, 1998; Sullivan et al., 1998).
Researchers have long established the contribution of
the HPA axis to anxiety but have been perplexed by
how it is regulated. They are buoyed by new findings
about the roles of the hippocampus and the amygdala.
The hippocampus and the amygdala govern
memory storage and emotions, respectively, among
their other functions. The hippocampus is considered
important in verbal memory, especially of time and
place for events with strong emotional overtones
(McEwen, 1998). The hippocampus and amygdala are
major nuclei of the limbic system, a pathway known to
underlie emotions. There are anatomical projections
between the hippocampus, amygdala, and
hypothalamus (Jacobson & Sapolsky, 1991; Charney &
Deutch, 1996; Coplan & Lydiard, 1998).
Studies of emotional processing in rodents
(Rogan & LeDoux, 1996) and in humans with brain
lesions (Adolphs et al., 1998) have identified the
amygdala as critical to fear responses. Sensory
information enters the lateral amygdala, from which
processed information is passed to the central nucleus,
the major output nucleus of the amygdala. The central
nucleus projects, in turn, to multiple brain systems
involved in the physiologic and behavioral responses to
fear. Projections to different regions of the
hypothalamus activate the sympathetic nervous system
and induce the release of stress hormones, such as
CRH. The production of CRH in the paraventricular
nucleus of the hypothalamus activates a cascade leading
to release of glucocorticoids from the adrenal cortex.
Projections from the central nucleus innervate different
parts of the periaqueductal gray matter, which initiates
descending analgesic responses (involving the body's
endogenous opioids) that can suppress pain in an
emergency, and which also activates species-typical
defensive responses (e.g., many animals freeze when
fearful) (Davis, 1997 ).
Anxiety differs from fear in that the fear-
producing stimulus is either not present or not
immediately threatening, but in anticipation of danger,
the same arousal, vigilance, physiologic preparedness,
and negative affects and cognitions occur (LeDoux,
1996). Different types of internal or external factors or
triggers act to produce the anxiety symptoms of panic
disorder, agoraphobia, post-traumatic stress disorder,
specific phobias, and generalized anxiety disorder, and
the prominent anxiety that commonly occurs in major
depression. It is currently a matter of research to
determine whether dysregulation of these fear pathways
leads to the symptoms of anxiety disorders. It has now
been established, using noninvasive neuroimaging, that
the human amygdala is also involved in fear responses
(Breiter et al., 1996). Fearful facial expressions have
been shown to activate the amygdala in MRI studies of
normal human subjects (Breiter et al., 1996). Functional
imaging studies in anxiety disorders, such as PET
studies of brain activation in phobias (Rauch et al.,
1995), are also beginning to investigate the precise
neural circuits involved in the anxiety disorders.
What is especially exciting is that
neuroimaging has furnished direct evidence in humans
of the damaging effects of glucocorticoids. In people
with post-traumatic stress disorder, neuroimaging
studies have found a reduction in the size of the
hippocampus. The reduced volume appears to reflect
the atrophy of dendrites—the receptive portion of nerve
cells—in a select region of the hippocampus. Similarly,
animals exposed to chronic psychosocial stress display
atrophy in the same hippocampal region (McEwen &
Magarinos, 1997). Stress-induced increases in
glucocorticoids specially corticosterone are thought to
be responsible for the atrophy (McEwen, 1998). If the
hippocampus is impaired, the individual is thought to be
less able to draw on memory to evaluate the nature of
the stressor (McEwen, 1998).
Almokhtar A. Adwas et al., East African Scholars J Med Sci; Vol-2, Iss-10 (Oct, 2019): 580-591
© East African Scholars Publisher, Kenya 584
6. Treatment of anxiety
Drugs to reduce anxiety have been used by
human beings for thousands of years. One of the first
anxiolytics and one that continues to be used by humans
is ethanol. A number of other drugs including the
barbiturates and the carbamates (meprobamate) were
used in the first half of the 20th century and some
continue to be used today.
6.1. Serotonin Receptor Modulators and Reuptake
Inhibitors
Serotonin has long been viewed as a
neurotransmitter involved in regulating emotional
states. Of the 14 or so mammalian serotonin receptor
subtypes that have been described in the literature, at
least four have been implicated in anxiety in various
animal models (Lucki, 1996). As reported by Lucki,
1996 the original hypothesis implicating serotonin in
anxiety surfaced from observations that reduced levels
of serotonin can produce anxiolytic effects. One of the
receptor subtypes implicated in anxiety is the serotonin
1A receptor subtype (5HT1A), which is an auto
receptor located presynaprically on serotonin neurons.
When stimulated, this receptor inhibits the synthesis
and secretion of serotonin. The 5-HT1A receptor
agonist buspirone exhibits anxiolytic effects in animals
and was approved by the Food and Drug Administration
(FDA) in 1986 for human generalized anxiety disorder.
Other serotonin receptors potentially involved in
anxiety include the 5-HT2A, 5-HT2C and 5-HT3
receptors. Antagonists for the 5-HT2A receptor, like
ritanserin, exhibit anxiolytic effects in some animal
models (Critchley and Handley, 1987; Gleeson et al.,
1989). Likewise, blockade of the 5-HT2C receptor
produces anxiolytic effects in animals and prevents the
anxiogenic effects of m-CPP (Kennett et al., 1989).
Finally, the 5-HT3 receptor antagonist ondansetron was
reported to be anxiolytic in some animal models
(Costall and Naylor, 1991).
Advances in molecular biology has led to the
development of serotonin receptor gene knockout
methodology, which generates mice lacking the 5-
HT1A receptor, allowing for the evaluation of this
receptor subtype in a variety of measurable behaviors.
Ramboz et al., 1998 reported results consistent with the
5-HT1A agonist's data cited above. Mice lacking this
receptor displayed less exploratory activity in an open
field and more anxious behavior than the wild types in
the elevated plus maze. According to the serotonin
hypothesis of anxiety (Johnson and file, 1986),
removing the negative feedback control of 5-HT with
the 5-HT1A receptor knockout animals should result in
increased levels of 5-HT in the synaptic cleft, which
would be expected to lead to the anxiogenic behavior.
However, Ramboz et al. 1998, reported normal levels
of 5-HT, which confuses the issues related to anxiety
modulation and serotonin levels.
In 1986, the FDA approved the 5-HT1A partial
agonist, buspirone for generalized anxiety disorder.
This drug was the first to challenge the benzodiazepines
for this patient group and was generally perceived as an
improvement because of the lack of benzodiazepine
side effects. The efficacy of buspirone, however, was
not the same as that of the benzodiazepines in terms of
its delayed onset of action, and it is generally accepted
that when buspirone offers clinical benefit to GAD
patients, it takes 3 to 4 weeks to match the efficacy of
benzodiazepines such as diazepam and alprazolam
(Coplan et al., 1995). The 5-HT1A partial agonist
properties of buspirone are believed to account for its
clinical effects, but it should be noted that the drug is
also a D2 antagonist and is extensively metabolized.
One of the major metabolites, 1-pyrimidinylpiperazine
(l-PP), may contribute to the pharmacologic activity of
buspirone (Mahmood and Sahajwalla, 1999). In a
double-blind, placebo-controlled study of buspirone in
GAD patients (Laakmann et al., 1998), the drug was
reported to be as efficacious as lorazepam at the end of
a 4-week treatment period. After the drugs were
discontinued, however, the lorazepam-treated patients
worsened whereas the buspirone-treated subjects
maintained clinical improvement. Thus, there continues
to be evidence that buspirone is effective in GAD.
The development of selective serotonin
reuptake inhibitors (SSRIs) in the 1980s and 1990s
widely expanded the treatment for depressive disorders,
and these drugs (fluoxetine, sertraline, venlafaxin,
paroxetine) have recently made inroads in treating
anxiety disorders such as panic, obsessivecompulsive
disorder, social phobia, and GAD. Successful treatment
of GAD with a class of drugs working through the
serotoninergic system will come from the SSRIs (Rocca
et al., 1997).
OCD is a chronic, disabling anxiety disorder.
In a review of the diagnosis and treatment of OCD,
Goodman, 1999 states that the backbone of
pharmacologic treatment for OCD is a 10- to 12-week
trial with an SSRIs in adequate doses. It is clear from a
review of the role of the 5-HT1A receptor (Coplan et
al., 1995) in OCD that partial agonists such as
buspirone are generally ineffective in treating OCD.
The authors also note that in studying the potential to
augment efficacy of the standard OCD medication,
buspirone was not different from placebo as an
augmenting agent. Drugs that work through other
serotonin receptor subtypes also appear to be ineffective
in treating OCD. Thus, drugs modifying the 5-HT1A, 5-
HT1D and 5-HT3 receptors appear ineffective in
treating OCD symptoms and rule out a critical
involvement of these receptor subtypes in OCD
(Broocks et al., 1998; Pian et al., 1998).
Almokhtar A. Adwas et al., East African Scholars J Med Sci; Vol-2, Iss-10 (Oct, 2019): 580-591
© East African Scholars Publisher, Kenya 585
In the past, tricyclic antidepressants (TCAss)
and monoamine oxidase inhibitors, as well as high
potency benzodiazepines, have been used to treat
patients with panic disorder. The SSRIs have also been
added to the list of effective agents for the disorder. In
reviewing the pharmacotherapy of panic disorder, den
Boer, 1998 notes that antidepressants are more effective
than benzodiazepines in reducing associated depressive
symptomatology and are at least as effective for
improving anxiety, agoraphobia, and overall
impairment. Bell and Nutt, 1998 remark that SSRIs
improve 60% to 70% of panic patients, a similar
percentage to those seen with the TCAs.
Like OCD, panic disorder is well treated by
SSRIs but does not appear to be effectively treated by
receptor specific compounds. Coplan et al., 1995
reviewed the role of 5HT 1A drugs such as buspirone in
panic disorder and reported that buspirone does not
significantly treat panic in several well-controlled
studies. Using the 5-HT1A receptor agonist flesinoxan,
ikvan Vliet et al., 1996 reported a worsening of
symptoms in panic patients treated with high doses of
the drug. It has also been reported that the 5-HT2A/2C
antagonist ritanserin had no effects on panic attacks or
phobic avoidance, and a similar negative finding has
been reported with the 5-HT3 antagonist ondansetron.
6.2. Γ-Aminobutyric Acid Receptor Modulators
(Benzodiazepines and Related Drugs)
A majority of the synapses in the
mammalian CNS use the amino acids I-glutamic acid,
glycine, or γ-aminobutyric acid (GABA) for signaling.
GABA is formed by the decarboxylation of I-glutamate,
stored in neurons, and released, and its action is
terminated by reuptake; GABA's action mimics the
naturally occurring inhibitory transmission in the
mammalian nervous system. Because of these findings,
it has been accepted for over 20 years that GABA
fulfills the characteristics of a neurotransmitter (Paul,
1995). Along with I-glutamate, acetylcholine, and
serotonin, GABA possesses two different types of
receptor conserved across different species and phyla
that control both excitation and inhibition. Molecular
biological studies of the receptors causing these effects
have indicated that GABA's effects on ionic
transmission (ionotropic) and metabolism
(metabotropic) are mediated by proteins in two different
superfamilies. The first superfamily (GABAAreceptors)
is a set of ligand-gated ion channels (ligand-gated
superfamily) that convey GABA's effects on fast
synaptic transmission (Siegharr, 1995). When a
GABAA receptor is activated, an ion channel is opened
(gated) and this allows chloride to enter the cell; the
usual result of chloride entry is a slowing of neuronal
activity through hyperpolarization of the cell membrane
potential. The second superfamily (GABAB) is slower,
mediating GABA's action on intracellular effectors
through a seven transmembrane spanning receptor
(serpentine superfamily) that modulates the action of
certain guanine nucleotide binding proteins (G proteins)
(Kaupmann et al., 1997). Through their activity on
other effector systems, G proteins can change second
messenger levels, altering signal transduction and gene
expression, or open ion channels that are dependent on
the G-protein subunit activities (Wess, 1997). Both
excitatory and inhibitory activities are possible on a
time scale that is longer than GABAA receptor
mediated events. There is extensive heterogeneity in the
structure of the GABAA receptor members of the
ligand-gated superfamily. These receptors are the
targets of a number of widely used and prescribed drugs
for sleep, anxiety, seizure disorders, and cognitive
enhancement; they may also contribute to mediating the
effects of ethanol on the body.
It is well established that the GABAA
receptors possess binding sites for the neurotransmitter
GABA, as well as allosteric modulatory sites for
benzodiazepines, barbiturates, neurosteroids,
anesthetics, and convulsants (Tallman et al., 1980;
Tallman and Gallager, 1985).
6.3. Corticotrophin-Releasing Factor Modulators
Corticotrophin-releasing factor (CRF) is a 41
amino acid peptide that plays an important role in
mediating the body‘s physiologic and behavioral
responses to stress (Koob et al, 1993). Figure (1)
illustrates that this role of CRF may be mediated by
multiple sites of action. As a secretagogue, CRF
stimulates the release of adrenocorticotropic hormone
(ACTH) from the pituitary. In addition, CRF plays a
neurotransmitter or neuromodulatory role through
neurons and receptors distributed in diverse brain
regions (DeSouza and Grigoriadis, 1995). CRF neurons,
localized in the hypothalamic periventricular nucleus,
are a major mediator of stress-induced activation of the
hypothalamic-pituitary-adrenal (HPA) axis, whereas
pathways innervating limbic and cortical areas are
thought to mediate the behavioral effects of CRF. There
is a large body of both preclinical and clinical literature
implicating a key role of CRF in affective disorders
such as anxiety and depression. A significant clinical
literature suggests that dysfunctions of CRF in its role
as a hormone in the HPA axis or as a neurotransmitter
in the brain may contribute to the etiology of a variety
of psychiatric conditions, including anxiety and
depression (Gold et al., 1995). The link between CRF
and depression is particularly strong, as numerous
clinical studies have demonstrated that depressed
patients show elevated cerebrospinal fluid (CSF) levels
of CRF, elevated plasma cortisol, and a blunted ACTH
response following intravenous CRF. Successful
antidepressant treatment was shown to have a
normalizing effect on CRF levels. A role of CRF in
anxiety disorders has also been postulated, though the
clinical evidence is not as strong as it is for depression
(Arborelius et al., 1999). Preclinical studies have
demonstrated that CRF administered exogenously into
the central nervous system (CNS) can produce
Almokhtar A. Adwas et al., East African Scholars J Med Sci; Vol-2, Iss-10 (Oct, 2019): 580-591
© East African Scholars Publisher, Kenya 586
behaviors indicative of anxiety and depression, for
example, heightened startle responses, anxiogenic
behaviors on the elevated plus maze, decreased food
consumption, and altered sleep patterns. The anxiogenic
effects of CRF are not blocked by adrenalectomy,
suggesting that they are centrally mediated effects
occurring independently of the HPA axis (Berridge and
Dunn, 1989a). Other studies strengthening the link
between CRF and anxiety include recent work by Kalin
et al. (2000) demonstrating that a ‗‗fearful‘‘ phenotype
in monkeys is associated with increased pituitary-
adrenal activity and increased brain CRF levels. Other
studies have shown that exposure to early postnatal
separation stress in rat pups results in elevated levels of
CRF messenger RNA (mRNA) in brain regions
including the paraventricular nucleus (PVN) and the
central nucleus of the amygdala (Heim et al., 1997;
Plotsky and Meaney, 1993). CRF acts through two Gs-
protein coupled receptors, the CRF-1 and CRF-2
receptor subtypes (Perrin and Vale, 2000; Dieterich et
al., 1997). CRF-1 receptors show homology to a
number of other neuropeptide receptors, including
vasointestinal peptide (VIP) and calcitonin (Perrin and
Vale, 2000).
Figure1. The role of corticotrophin-releasing factor (DeSouza and Grigoriadis, 1995)
CRF-1 and CRF-2 receptors have different
pharmacology and different localizations in the brain
and periphery. In situ hybridization and receptor
autoradiography techniques have been used to map the
relative distributions of CRF-1 and CRF-2 receptors in
the rat brain (Chalmers et al., 1995; Primus et al.,
1997). High expression of CRF-1 receptors was seen in
the pituitary, and in a number of brain regions including
the PVN of the hypothalamus, cerebral cortex, olfactory
bulb, cerebellar cortex, and basolateral and medial
amygdala. In contrast, high densities of CRF-2 are
found in more circumscribed regions, including the
lateral septum, ventromedial nucleus of the thalamus,
and choroid plexus. Moderate densities of CRF-2
receptors were reported for the medial amygdala and
dorsal raphe nucleus (Sanchez and Young, 1999). CRF
receptors utilize 3',5'-cyclic adenosine monophosphate
(cAMP) as a second messenger in the pituitary and
brain and can be regulated by chronic activation.
Thus, desensitization following exposure to CRF has
been demonstrated both in vitro (Dieterich et al., 1966)
and in vivo (Hauger and Aguilera, 1993). Furthermore,
chronic stress can down-regulate CRF receptors and
decrease CRF-stimulated cAMP production in multiple
brain areas (Aguilera et al, 1987; Anderson and Kant,
1993). Down-regulation of pituitary CRF receptors
following adrenalectomy presumably results from
decreased ACTH mediated inhibitory feedback, which
produces excess CRF stimulation. There are a number
of pharmacologic agents available for dissecting the
functional significance of CRF-1 and CRF-2 receptors.
Much work has been carried out using the peptide
antagonists α-helical-CRF and D-Phe CRF. However,
these compounds have shortcomings in that they do not
penetrate the CNS and therefore have to be
administered intracerebro-ventricular (icv).
Furthermore, they do not discriminate between CRF
receptor subtypes and therefore do not allow a
determination of their relative contributions to behavior.
More recently, the development of selective,
nonpeptidic antagonists of the CRF-1 receptor such as
CP 154,526 (Schulz et al., 1996) have provided
important pharmacologic tools for the analysis of CRF-
1 receptor function. Mutation studies have
demonstrated that peptide and nonpeptide antagonists
bind to different domains of the CRF-1 receptor (Perrin
and Vale, 2000). To date, selective CRF-2 antagonists
have not been described, though recently, non peptide
dual antagonists of the CRF-1 and CRF-2 receptors
have been described (Luthin and Rabinovich, 1999).
Studies utilizing transgenic and knockout mouse models
have provided important information with regard to the
contribution of CRF and CRF receptor subtypes to
processes including energy balance, emotionality,
cognition, and drug dependence (Contarino et al, 1999).
Over expression of CRF in transgenic mice produced
anxiogenic effects using either the black-white box test
(Heinrichs, et al, 1997) or the elevated plus maze
(Stenzel-Poore et al, 1994). The latter effect was
reversed by central administration of the CRF receptor
antagonist a-helical CRF, but not by adrenalectomy,
supporting the role of central CRF pathways
Almokhtar A. Adwas et al., East African Scholars J Med Sci; Vol-2, Iss-10 (Oct, 2019): 580-591
© East African Scholars Publisher, Kenya 587
independent of the HPA axis (Stenzel-Poore and
Heinrichs, 1994). Studies using antisense directed
against CRF in rats have produced evidence of
anxiolytic activity (Skutella et al., 1998). Finally, over
expression of CRF-BP is anxiolytic, whereas binding
protein knockout mice (in which free CRF levels are
elevated) display an anxiogenic phenotype in the
elevated plus maze (Ramesh et al., 1998). These data
generally support the link between CRF and anxiety.
More recently, several studies have highlighted
the importance of the CRF-l receptor subtype in
anxiety. CRF1 knockout mice demonstrated a
diminished anxiogenic response on the elevated plus
maze and decreased ACTH and corticosterone
responses to restraint stress (Smith et al., 1999). Similar
findings were reported, using the blackwhite box
anxiety paradigm (Timpl et al., 1998). Furthermore,
inactivation of the CRF-l receptor with an antisense
oligonucleotide was shown to reduce the anxiogenic
effect of intraventricularly administered CRF (Skutella
et al., 1998). Liebsch et al., 1995 provided evidence of
anatomic localization by showing anxiolytic activity
from CRF-l antisense that was chronically infused into
the central nucleus of the amygdala, an area of the
limbic system shown by Davis M, 1997; LeDoux J,
1996, and others to be important in mediating fear and
anxiety processes. Finally, CRF-2 knockout mice show
anxiety-like behavior and are hypersensitive to stress
(Bale et al., 2000), indicating that the CRF-2 receptor
has an opposite functional role to that of the CRF-l
receptor. Thus, it could be argued that CRF-2 agonists,
rather than antagonists, might be potentially useful as
anxiolytic agents.
Another potential use for CRF antagonists is in
the treatment of drug abuse. Several lines of evidence
suggest that during the period of withdrawal from drugs
of abuse such as ethanol, morphine, and cocaine, there
is an activation of central CRF pathways. Anxiety is
among the many physical symptoms of drug
withdrawal, and given the link that has been made
between CRF and anxiety, it is not surprising that CRF-
l receptor knockout mice demonstrated decreased
anxiety responses during withdrawal from alcohol
(Timpl et al., 1998).
6.4. Neurokinin Receptor Antagonists
There is an extensive literature demonstrating
that the peptide tachykinins such as substance P and
their associated receptors have a widespread
distribution in the brain, spinal cord, and periphery, and
may play important roles in chronic pain and
inflammation processes (Otsuka and Yoshioka, 1993;
Khawaja and Rogers, 1996; Longmore et al., 1997;
Mantyh et al., 1989; Tooney et al., 2000). In addition,
anatomic and physiologic evidence has also indicated
that these peptides limbic structures that are involved in
the regulation of mood, such as the amygdala,
hypothalamus, and periaqueductal gray (Culman and
Unger, 1995). This notion is supported by early positive
clinical findings using a selective neurokinin-l (NK-l)
antagonist for the treatment of depression and anxiety
(Kramer et al., 1998). Tachykinins collectively refer to
small peptides that include substance P (SP), neurokinin
A (NK-A), and neurokinin B (NK-B). These peptides
show preferential affinity for three receptors, designated
NK-l, NK-2, and NK-3, respectively, which are
members of the seven-transmembrane, G-protein-
coupled family. Of these three receptors, NK-l and NK-
3 are found in the brain, whereas NK-2 is primarily
localized peripherally in smooth muscle of the
respiratory, urinary, and gastrointestinal tracts.
Neurokinin receptors are localized in a number of
different brain areas that are implicated in anxiety,
including the amygdala, hypothalamus, and locus
coeruleus.
Studies assessing the effects of direct
administration of neurokinin agonists such as substance
P into the nervous system are complicated by the
findings that, depending on factors such as the site and
dose, opposite effects on behavior may be achieved
(Kramer et al, 1998).
6.5. Cholecystokinin B antagonists
Cholecystokinin (CCK) is a peptide found
extensively both in the gut (where it was originally
identified) and in the brain (Mutt and Jorpes, 1971).
CCK exists in multiple forms, the most predominant of
which is CCK octapeptide (CCK8) and, to a lesser
extent, CCK tetrapeptide (CCK4) (Hokfel et al., 1985).
CCK is colocalized with a number of different
neurotransmitters, including serotonin, dopamine,
GABA, substance P, neuropeptide Y, and VIP. CCK-
like immunoreactivity has been demonstrated in
anatomic regions that include the amygdala, cerebral
cortex, hippocampus, striatum, hypothalamus, and
spinal cord (Emson et al., 1982). There are two
subtypes of CCK receptor, CCKA (sulfated CCK) and
CCKB (unsulfated CCK) (Moran et al., 1986). CCKA
receptors are localized in the nucleus accumbens,
posterior hypothalamus, and area postrema. CCKB
receptors are localized in cortex, olfactory bulb, nucleus
accumbens, and other brain areas (Pisegna et al., 1992).
7.CONCLUSION
It can be concluded that anxiety is manifest by
disturbances of mood, thinking, behaviour, and
physiological activity and accompanying disturbances
of sleep, concentration, social and/or occupational
functioning. Also, it is associated with restlessness,
feeling keyed up or on edge, being easily fatigued,
difficulty in concentrating or mind going blank,
irritability, muscle tension, and irritability. The etiology
of anxiety may include stress, diabetes, depression,
genetic, and environmental factors. Drugs to reduce
anxiety have been used by human beings for thousands
of years. The drugs were used to reduce anxiety,
including the barbiturates and the carbamates
Almokhtar A. Adwas et al., East African Scholars J Med Sci; Vol-2, Iss-10 (Oct, 2019): 580-591
© East African Scholars Publisher, Kenya 588
(meprobamate) drugs were used for treatment of
anxiety in the first half of the 20th century and some
continue to be used today. Anxiety disorders should be
treated with psychological therapy, pharmacotherapy,
or a combination of both.
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