Neurotransmitters
  • permit exchange of information among neurons
  • permit exchange of information between neurons and other cells
  • classified according to size:
    • biogenic amines, amino acids = small-molecule messengers
    • neuropeptides = larger molecules, more numerous
  • may be localized to specific regions or widespread
  • pathways may target specific brain regions (dopamine, norepinephrine)

  • Acetylcholine (ACh)
    • first identified in 1914 by Henry Hallett Dale for its actions on heart tissue.
    • was confirmed as a neurotransmitter by Otto Loewi who initially gave it the name vagusstoff because it was released from the vagus nerve.
    • the first neurotransmitter to be identified.
    • Stimulates parasympathetic nervous system, motor control
    • predominant neurotransmitter at neuromuscular junction
    • stimulates muscle contractions
    • influences alertness, attention, memory
    • requires choline - supplied by liver, kidneys, egg yolks, seeds, veggies, legumes
    • synthesized by the liver, recycled in the brain - easily crosses BBB
    • binds to post-synaptic receptors:
      • nicotinic receptors - excitatory response
      • muscarinic receptors - inhibitory response
    • Implicated in Huntington's disease - degeneration of Striatum
    • important in sleep/arousal (RAS) - cortical activation, REM sleep
    • hippocampus - implicated in Alzhiemer's disease
    • projections to "neocortex", hippocampus, olefactory bulb, cingulate

  • Serotonin
    • widely distributed, originates in raphe nuclei (brainstem)
    • is believed to play an important role in (the inhibition of) anger, aggression, body temperature, mood, sleep, vomiting, sexuality, and appetite
    • project to cerebellum, medulla, limbic system

  • Norepinephrine (NE)
    • primarilly from the locus ceruleus (Latin for 'the blue spot')
    • synthesized from dopamine, released from the adrenal medulla into the blood as a hormone, and as a neurotransmitter in the central nervous system and sympathetic nervous system where it is released from noradrenergic neurons. The actions of norepinephrine are carried out via the binding to adrenergic receptors.
    • important in mood regulation, arousal, attemtion (maintaining, focusing), memory, processing speed
    • pathways project to forebrain, cerebellum, spinal cord

  • Dopamine
  • functions as a neurotransmitter, activating five types of dopamine receptors
  • produced in several areas of the brain, including the substantia nigra
  • important roles in behavior and cognition, motor activity, motivation and reward, regulation of milk production, sleep, mood, attention, and learning.
  • Via the dopamine receptors D1, D2, D3, D4 and D5, dopamine acts as both an excitatory and inhibitory neurotransmitter
    • mesocortical pathway projects the frontal lobes (cognitive funcitoning, motivation, and emotional control)
    • mesolimbic projects to the midbrain then to the nucleus accumbens, which is located in the striatum and is a part of the limbic system (reward, pleasure)
    • nigrostriatal pathway connects the substantia nigra with the striatum... is particularly involved in the production of movement, as part of a system called the basal ganglia motor loop.

     
    The pigment in the substantia nigra is dark (arrows) because of the presence of brown neuromelanin in neurons

  • Amino acids:
    • GABA - quite common, 1/3 of all synapses receptive to GABA, inhibitory
    • glutamate - excitatory, widely distributed

    Damage to the Brain