Neuropharmacology Quiz on Inhibitory Mechanisms
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Questions and Answers

Which of the following substances are known as behavioral stimulants that can mimic or potentiate norepinephrine (NA)?

  • Strychnine
  • Amitriptyline (correct)
  • Methylphenidate
  • Cocaine (correct)

    • What type of drugs are classified as clinical antidepressants that potentially reinforce norepinephrine?

  • Benzphetamine
  • Phenmetrazine
  • Tranylcypromine (correct)
  • Strychnine

    • Which of the following substances is primarily known for blocking inhibitory synapses within the brain?

  • Amitriptyline
  • Pentylenetetrazol (correct)
  • Cocaine
  • Benzphetamine

    • Which of the following can be considered as miscellaneous behavioral stimulants, albeit with less potency than amphetamines?

    <p>Methylphenidate</p> Signup and view all the answers

    What is the primary therapeutic classification for drugs like amitriptyline in relation to norepinephrine?

    <p>Clinical antidepressants</p> Signup and view all the answers

    Which of the following statements about miscellaneous behavioral stimulants is true?

    <p>They act on unknown mechanisms.</p> Signup and view all the answers

    Which of the following is not a known convulsant?

    <p>Benzphetamine</p> Signup and view all the answers

    What is a characteristic of behavioral stimulants compared to miscellaneous behavioral stimulants?

    <p>They mimic norepinephrine effects.</p> Signup and view all the answers

    What is one way that amphetamine affects norepinephrine (NE) action at the synapse?

    <p>It triggers release of NE from the presynaptic terminal.</p> Signup and view all the answers

    How do MAO inhibitors (MAOIs) affect norepinephrine levels in the brain?

    <p>By blocking NE metabolic destruction.</p> Signup and view all the answers

    Which statement about caffeine as a general cellular stimulant is true?

    <p>Caffeine is less effective than more specific stimulants.</p> Signup and view all the answers

    What mechanism primarily terminates norepinephrine action at the synaptic cleft?

    <p>Active uptake back into the synaptic cleft.</p> Signup and view all the answers

    Which effect does nicotine have on acetylcholine synapses?

    <p>It stimulates certain acetylcholine synapses.</p> Signup and view all the answers

    What is the primary action of picrotoxin related to presynaptic responses?

    <p>It blocks presynaptic inhibitory responses.</p> Signup and view all the answers

    Which of the following pathways does not relate to how drugs increase NE activity at the synapse?

    <p>Decreased release of NE from presynaptic neurons.</p> Signup and view all the answers

    What is a common characteristic of behavioral stimulants like amphetamines and cocaine?

    <p>They promote increased rates of norepinephrine action.</p> Signup and view all the answers

    Which statement accurately describes strychnine's mechanism of action?

    <p>It blocks direct and indirect inhibitory responses.</p> Signup and view all the answers

    Which action mechanism allows drugs to mimic the effects of norepinephrine?

    <p>Direct stimulation of postsynaptic NE receptors.</p> Signup and view all the answers

    How does digoxin affect neuronal excitability?

    <p>It blocks Na+/K+ ATPase, producing excitation.</p> Signup and view all the answers

    Which mechanism contributes to the enhanced-excitatory responses of stimulant drugs?

    <p>Blocking neurotransmitter reuptake enzymes.</p> Signup and view all the answers

    What kind of response does leptazole produce at the synaptic level?

    <p>It allows repetitive action of the stimulus.</p> Signup and view all the answers

    Which of the following best describes a characteristic of central stimulants?

    <p>They produce varied increases in behavioral activity.</p> Signup and view all the answers

    What is the effect of some barbiturates like DMBB based on their isomeric forms?

    <p>The dextro-isomer is convulsant while the laevo-rotatory form is depressant.</p> Signup and view all the answers

    Which of the following is NOT involved in the excitatory effects of stimulant drugs?

    <p>Prolonging the inhibitory actions of neurotransmitters.</p> Signup and view all the answers

    Which mechanism does amphetamine primarily utilize to affect norepinephrine (NE) levels?

    <p>Increased release of NE</p> Signup and view all the answers

    Which of the following drugs blocks the reabsorption of norepinephrine by the presynaptic nerve terminal?

    <p>Cocaine</p> Signup and view all the answers

    What effect does lithium have in the treatment of mania?

    <p>Blocks presynaptic release of NE</p> Signup and view all the answers

    Which CNS stimulant category is primarily focused on relieving depression without causing excitement?

    <p>Antidepressants</p> Signup and view all the answers

    What is a key effect of reserpine in the context of norepinephrine?

    <p>Depletes norepinephrine in the brain</p> Signup and view all the answers

    Cocaine's primary action on norepinephrine involves which of the following?

    <p>Inhibition of reabsorption of NE</p> Signup and view all the answers

    Which CNS stimulant is known to precipitate exaggerated spinal reflexes?

    <p>Strychnine</p> Signup and view all the answers

    What is the role of MAO-inhibiting antidepressants in the treatment of depression?

    <p>They inhibit the MAO enzyme</p> Signup and view all the answers

    What is the primary action of imipramine regarding norepinephrine?

    <p>Blocks uptake-1 of NA</p> Signup and view all the answers

    Which neurotransmitter is primarily involved in the activation of the transition from NREM to REM sleep?

    <p>Serotonin (5-HT)</p> Signup and view all the answers

    What is the mechanism of action of lithium in manic depressive illness?

    <p>Mood stabilization</p> Signup and view all the answers

    What is a common consequence of spinal cord stimulants such as strychnine?

    <p>Tonic fits (convulsions)</p> Signup and view all the answers

    Which of the following is NOT considered a psychoactivator?

    <p>Strychnine</p> Signup and view all the answers

    What often follows the initial event of exaggerated afferent stimuli from spinal cord stimulants?

    <p>Activation of spinal motor</p> Signup and view all the answers

    How do analeptics generally function?

    <p>As stimulants to revitalizing respiration</p> Signup and view all the answers

    What is one potential outcome during hypoxic episodes induced by spinal cord stimulants?

    <p>Paralysis of vital brainstem centres</p> Signup and view all the answers

    Study Notes

    Picrotoxin

    • Blocks presynaptic inhibitory responses in the CNS, particularly in the caudate nucleus.
    • Specifically blocks GABA-mediated presynaptic inhibition.
    • Does not cause stimulant (excitation) action when blocking presynaptic inhibition of drugs like mephenesin.

    Strychnine

    • An alkaloid extracted from nux-vomica seeds, historically used as rat poison and in suicide attempts.
    • Blocks various forms of direct and indirect inhibitory responses in the spinal cord.
    • Blocks recurrent inhibitory processes, such as those seen in Renshaw cells, without affecting their firing level.
    • Glycine is also involved in the terminal of Renshaw cells and the cell body of the postsynaptic neuron, acting as an inter-neuron collateral.

    Cardiac Glycosides

    • The Na+/K+ ATPase pump system controls neuronal excitability.
    • Activation of this pump leads to inhibition, while blockade causes excitation.
    • Digoxin, a cardiac glycoside, blocks the Na+/K+ ATPase pump, leading to an excitatory cardiac effect and convulsions in some laboratory animals.

    Mechanisms of Stimulant Drugs' Enhanced Excitatory Neuronal Responses

    • Increased release of neurotransmitters by nerve impulses.
    • Increased amount of excitatory neurotransmitters.
    • Prolongation of excitatory neurotransmitter action by blocking its dissipating enzyme.
    • Increased sensitivity of postsynaptic membranes to neurotransmitters.
    • Leptazole decreases synaptic recovery time, allowing for repetitive action of a stimulus.
    • Leptazole acts directly on the medullary center, making it a good analeptic.
    • Leptazole specifically antagonizes trimethadione, a drug used for petit-mal epilepsy.
    • Leptazole does not affect neuronal resistance to impulses.
    • Barbiturates, such as CHEB (5-cyclohexilydine ethyl barbituric acid) and DMBB, have dextro-isomers that are convulsant (stimulant) and laevo-rotatory forms that are depressant.

    Classification of CNS Stimulants

    • CNS stimulants are divided into five categories based on their mechanisms of action or sites of action.
    • Reinforcers of NA (mimicking or potentiating it):
      • Behavioral stimulants (e.g., cocaine, amphetamines)
      • Clinical antidepressants (e.g., tranylcypromine (MAOIs), amitriptyline (TCAs))
    • Miscellaneous behavioral stimulants (e.g., methylphenidate, phenmetrazine, benzphetamine)
    • Convulsants (e.g., strychnine, picrotoxin, pentylenetetrazol, bicuculline) primarily block inhibitory synapses within the brain.
    • General cellular stimulants (e.g., caffeine) increase cellular metabolism within the brain, leading to nonspecific and less potent behavioral stimulation.
    • Stimulants of certain acetylcholine synapses (e.g., nicotine)

    Mechanisms of Behavioral Stimulants and Antidepressants:

    • Amphetamine, cocaine, and clinical antidepressants potentiate NE action at the synapse, occurring in five ways:
      • Increased rate of NE synthesis.
      • Decreased rate of NE metabolic destruction by inhibiting MAO, an enzyme that metabolizes NE within presynaptic nerve terminals.
      • Triggering the release of NE from presynaptic terminals.
      • Prolongation of NE action at its postsynaptic receptor by blocking its reuptake, which is the primary mechanism for terminating NE action.
      • Direct stimulation of postsynaptic NE receptors.
    • Summary of actions:
      • Amphetamine: increases NE release, directly stimulates postsynaptic NE receptors, and blocks NE reabsorption.
      • Cocaine: blocks NE reabsorption.
      • Tricyclic antidepressants: block NE reabsorption.
      • MAO inhibitors: inhibit MAO.
      • Lithium: blocks presynaptic release of NE, decreasing synaptic NE availability.

    NE Theory of Mania and Depression:

    • The NE system plays a role in emotional behavior.
    • Reserpine: an antipsychotic drug depletes NE in the brain, causing severe behavioral depression.
    • Lithium: used to treat mania, blocks presynaptic release of NE, reducing synaptic NE levels.
    • Lithium paradox: while lithium helps mania by blocking NE release, it can also cause depression, seemingly contradicting the NE hypothesis. This may be due to a slow reduction in NE during treatment, followed by a rebound effect leading to a period of depression.
    • Manic-depressive patients: experience mood swings, with fluctuating NE levels. As mania is alleviated, NE levels become more stable, reducing depressive episodes.

    Groups of CNS Stimulants:

    • Psychoactivators or mood elevators: increase mental activity and alertness (e.g., amphetamine, methylphenidate).
    • Analeptics: stimulate nerve cells of the midbrain and medulla, used to maintain respiration during depressant drug overdose (e.g., leptazol, ethamiran, picrotoxin).
    • Spinal cord stimulants: exaggerate spinal reflexes (e.g., strychnine).
    • Antidepressants: relieve depression without inducing excitement or delirium (e.g., imipramine, MAO-inhibitors).

    CNS Stimulants of Clinical Importance:

    • Antidepressants:
      • Imipramine: a tricyclic compound that blocks NE reuptake.
      • Monoamine oxidase inhibitors: divided into two groups.
      • Lithium: used to stabilize mood in manic-depressive illness.
    • Spinal cord stimulants: (strychnine and tetanus toxin): laboratory tools for studying anticonvulsant drugs, used to induce spinal cord convulsions; toxicological interest.
    • Analeptics: (picrotoxin, leptazol, nikethamide):
    • Psychoactivators: (amphetamine, methylphenidate, methylamphetamine): elevate mood and stimulate mental activity. Amphetamine's dextro-isomer (D-amphetamine) is particularly effective as a CNS stimulant.

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    Description

    Test your knowledge on neuropharmacology through questions focusing on picrotoxin, strychnine, and cardiac glycosides. This quiz explores the mechanisms of these compounds in the central nervous system, detailing their effects on neuronal excitability and inhibition. Delve into the intricacies of GABA-mediated processes and more.

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