CNS Pharmacology Flashcards
What are anxiolytic drugs?
Drugs used to treat anxiety
What are hypnotic drugs?
Drugs used to treat sleep disorders
What is anxiety?
Anticipatory fear response which is often independent of external events, general anxiety is an ongoing state of an excessive version of this
Panic disorders
Sudden attack of overwhelming fear, sweating, tachycardia, chest pains, trembling and choking
Has a genetic component
Phobias
Strong fear response to specific object or situations
Social anxiety
Fear of being with and interacting with people
PTSD
Anxiety triggered by recall of a stressful situation
OCD
Compulsive ritualistic behaviour driven by irrational anxiety
What is the elevated cross test?
Time animal spends in the safer environment and is less exposed is measured
Anxiolytic drugs reduce fear response so animals time spent in the more exposed environment will increase
What is the target for anxiolytics?
GABA receptors
GABA A receptors
Ionotropic with 5 subunits
Chloride selective
Mediate fast inhibitory transmission postsynaptically
What is the orthosteric site?
The agonist binding site responsible for switching on signalling by a receptor
What are allosteric sites?
Additional sites that don’t themselves switch on signalling, but modify the function or signalling of the agonist bound receptor
GABA A orthosteric agonists and antagonists
agonist is muscimol
antagonist is bicuculline/picrotoxin
Why does pharmacology involving GABA A vary in the CNS?
Different combinations of subunits are expressed in different parts of the brain so depending on the GABA A subunit composition, pharmacology varies
What are the physiological effects of benzodiazepine agonists?
Sedation, hypnosis, anterograde amnesia, anti-convulsant, reduction of muscle tone
Why are benzodiazepines often abused after chronic clinical treatment and are linked to dependence and addiciton?
Activation of midbrain dopamine neurons which could possibly hijack the mesolimbic system
What are benzodiazepines?
Positive allosteric site regulators of GABA A receptors
Increase activity of GABA A receptor by increased Cl- current across membrane but only when GABA is present
How are benzos mechanism of action different to other anxiolytics?
Benzos increase probability of channels opening whereas barbituates and steroids increase mean open time
Both result in more current flow and increased response
Beta carboline
Negative allosteric regulator of GABA A that decreases channel openings
Anxiogenic and a proconvulsant
Flumanzenil
Antagonist at benzodiazepine site so it binds there but doesn’t effect receptor
Can be used to reverse effects of benzodiazepine overdose
Positive allosteric modulators of GABA
Stabilise the receptor in a state with increased affinity for GABA
Causes a leftward shift in conc response curve
Negative allosteric modulators of GABA
Stabilise the receptor in a state thta has reduced affinity for GABA
Remains closed or harder to open
What are the adverse effects of using benzodiazepine agonists?
Tolerance, misuse, physical dependence characterised by withdrawal- increased anxiety, insomnia, CNS excitability and convulsions
Propanolol
Beta blocker
Anti-depressants / SSRIs
Selective serotonin reuptake inhibitors- useful for generalised anxiety, phobias, PTSD and OCD
Buspirone
A 5HT1A partial agonist used for generalised anxiety
What other types of drugs can also be used for generalised anxiety?
Atypical antipsychotics and anti-epileptic drugs
What drugs are used to treat insomnia?
Drug choice depends on underlying cause and whether it is short term or chronic
Melatonin receptor agonists, orexin receptor antagonists, over the counter sleep aids (H1 receptor antagonists)
What are the three types of general anaesthetics?
Chemical- inhalational, nitrous oxide
Physical- low pressure or hypothermia
Intravenous- halogenated hydrocarbons like isofluorane, barbituates and steroids
How do general anaesthetics work?
Regulation of activity of neuronal ion channels, most increase GABA action at GABA A receptors
Volatile GAs bind at interface of alpha and beta subunits
Intravenous GAs bind only on beta subunit
How do ketamine and nitrous oxide work?
Blocking NMDA receptors
How does isoflurane work?
In the neurohypophyseal terminal it reversibly blocks Na+ currents and APs
In the rat calyx it reversibly reduces synaptic vesicle exocytosis
What are the effects of general anaesthetic on neuronal transmission when in low concentrations?
Synaptic transmission in the CNS is decreased, reticular formation is unconscious, effects on hippocampus mean short term amnesia, effects on thalamic sensory relay nuclei parts of the cortex mean analgesia, some inhibit spinal reflexes
What happens when general anaesthetics are in high concentrations?
All brain functions are affected- loss of motor control, reflexes, respiration, autonomic regulation
So absence of artificial respiration leads to death
How are general anaesthetics different to local ones?
Effects on axonal conduction is important for local anaesthetis but not for general ones
What are the 4 stages of anaesthesia?
Analgesia
Excitation
Surgical anaesthesia
Medullary paralysis
What stages should be avoided?
Excitation
Medullary paralysis- loss of cardiovascular refelxes and respiratory paralysis which causes death
What is the ideal for anaesthesia for surgery?
Rapid induction and loss of consciousness
Analgesia
Muscle relaxation
Rapid recovery
What are the advantages of intravenous GAs?
Easy to administer, rapid induction and rapid metabolism so faster recovery and less hangover
What are the disadvantages of intravenous GAs?
Pain at site of injection, complex pharmacokinetics, high lipid solubility means rapid induction but short duration of action due to redistribution, hangover from accumulation in body fat
Ketamine
Dissociative anaesthetic used in pediatrics and veterinary practice
Sensory loss, powerful analgesia, amnesia but no complete loss of consciousness and no respiratory depression
What is malignant hypothermia?
Can be triggered by halogenated general anaesthetics
Induces a drastic and uncontrolled increase in oxidative metabolism in skeletal muscle
Often inherited and is an autosomal dominant disorder
What does malginant hypothermia lead to?
Overwhelms the bodys capacity to supply oxygen and remove carbon dioxide and regulate body temp
Eventually leads to circulatory collapse and death if not immediately treated
What is dantrolene and what is it used for?
RYR antagonist and muscle relaxant that is given before anaesthesia to people that are susecptible to malignant hypothermia
What general anaesthetics can cause malignant hypothermia?
Volatile halogenated anaesthetics
Succinylcholin- neuromuscular blocking agent
What is constitutive activity?
Occasionally channels open in the absence of an agonist
What is an inverse agonist?
When bound they reduce constitutive activity
What is epilepsy?
Unprovoked seizures from high frequency discharge by a group of neurons
Spread can be partial or generalised
What are generalised seizures?
Involve both hemispheres of the brain
What are complex seizures?
Includes loss of conscious (simple seizures don’t)