Chapter 6 - Neurotransmitter Systems (Slide Notes pt 2)

Introduction to Neuroscience Notes

Overview of Cell Communication

  • Cell-to-cell communication is essential for various functions in the nervous system.
  • Mechanisms include chemical signals that control nerve impulses and influence neurotransmitter release.
  • Resting membrane potential: The state in which neurons maintain an electrical charge difference across their membrane (typically around -65 mV).
  • Action potential (AP):
  • A rapid change in membrane potential that occurs when a neuron is excited.
  • Triggered when the membrane potential reaches a threshold (usually -55 mV), resulting in depolarization.

Synaptic Transmission

  • Synaptic transmission involves the release of neurotransmitters from presynaptic neurons that bind to postsynaptic receptors, leading to changes in the postsynaptic cell.
  • Post-synaptic receptors determine the effect of a neurotransmitter:
  • Can lead to either excitation (EPSP) or inhibition (IPSP)
  • Example: Acetylcholine (ACh) can act on different types of receptors:
    • Nicotinic receptors (ionotropic): Found at neuromuscular junctions, lead to muscle contraction by allowing Na+ influx (EPSP).
    • Muscarinic receptors (metabotropic): Found in the heart, lead to inhibition by allowing K+ efflux (IPSP).
  • Glutamate as another example:
  • Acts on AMPA receptors (ionotropic) causing Na+ entry (EPSP).
  • Acts on NMDA receptors which require prior depolarization due to Mg++ blockage to allow Ca++ entry.

Types of Neurotransmitter Action

  • Neurotransmitter effects are mediated by the post-synaptic receptor type.
  • Autoreceptors: Located on presynaptic membranes, bind the neurotransmitter released by the neuron to regulate its further release.
  • Example: Norepinephrine (NE) acts as a neurotransmitter in noradrenergic synapses.

Pharmacological Effects on Neurotransmission

  1. Precursor Administration:
  • L-DOPA: A precursor for dopamine used in the treatment of Parkinson's disease.
  1. Facilitating Synaptic Release:
  • Example: Black Widow venom increases neurotransmitter release by creating pores for Ca2+ entry.
  1. Agonists:
  • Drugs that mimic or enhance neurotransmitter effects on postsynaptic receptors (e.g., Morphine, THC, Nicotine).
  1. Enzyme Inhibition:
  • Monoamine oxidase (MAO) inhibitors increase neurotransmitter levels by preventing their breakdown.
  • Drugs like nerve gases inhibit acetylcholinesterase (AChE) leading to increased levels of ACh.
  1. Reuptake Blockade:
  • Cocaine, Ritalin, and Adderall block the reuptake of neurotransmitters, thereby prolonging their action on receptors.

Opposing Effects on Neurotransmitters

  1. Synthesis Inhibition:
  • PCPA inhibits serotonin synthesis.
  1. Release Inhibition:
  • Botulinum toxin and tetanus toxin inhibit neurotransmitter release.
  1. Vesicular Uptake Prevention:
  • Reserpine prevents storage of neurotransmitters in vesicles.
  1. Antagonists:
  • Naloxone (Narcan): Blocks opioid receptors, used in cases of overdose.

Optogenetics as a Tool

  • Optogenetics: A technique using light-sensitive proteins to control neuronal activity with light, offering a method to study specific neurons without affecting others.
  • Channelrhodopsin (ChR2) allows sodium channels to open with light, exciting neurons.
  • Halorhodopsin (NpHR) can be used to silence neurons through light-induced chloride pumping.
  • Allows researchers to link cell types to specific functions in the brain separately.

Summary of Drug Actions

  • Drugs can either enhance or inhibit neurotransmitter function, leading to various therapeutic and adverse effects.
  • Understanding these mechanisms is critical in pharmacology and neuroscience for developing effective treatments for neurological disorders.