Peptides, Lipids and Gases

why are peptides, lipids nucleosides not considered traditional neurotransmitters

doesnt always satisfy all of criteria

• present in presynpatic terminals

• released from presynaptic terminals after neuron fires

• existence of receptors on postsynaptic neurons

peptide structure

composed of 2+ amino acids

peptide synthesis

in brain majority are not synthesised from smaller compounds but rather products of larger poly-peptides being broken down within neurons before release at terminal button

peptide release

serve as modulators - act as both neurotransmitters and hormones and often co-released with other neurotransmitters

endogenous opiods

class of peptides. highest density of opiod receptors in areas involved in pain

endogenous opiods vs opiates

• endo = originating internally

• opiate = drugs like heroin and morphine

heroin

highly addictive opiate that is a full agonist to endogenous opiods

use of buprenorphine

a partial agonist for opiods = used as treatment for heroin dependency

• manages withdrawal symptoms as agonises same effects but to a lesser degree

• high affinity for receptors = prevents people from high from taking heroin

naloxone

opioid antagonist used to reverse the effects of opioid overdose

• not for long term treatment as causes pretty immediate withdrawal symptoms

lipids

hydrophobic organic compounds including fats and waxes. primarily functions as energy storage, signaling and provides structural component of cell membrane

• synthesis of those that act as neurotransmitters unclear

endocannabinoids

lipid neurotransmitter endogenous cannabis-like substances

cannbinoid receptors

CB1 in brain and CB2 in peripheral tissues

• CB1 - thought responsible for main psychological effects

CB1 receptor

receptor activation = shortens duration of action potentials in presynaptic = decreases amount of neurotransmitters released

• modulates the modulators

effect of CB1 receptors in brain

• basal ganglia - movement

• cerebral cortex - higher cognitive function

• hypothalamus - appetite

• cerebellum - movement

• hippocampus - memory, learning, stress

• spinal cord - peripheral sensation incl pain

• medulla - nausea/vomitting, chemoreceptor trigger zone

neucleosides

subunits of nucleic acids. obtained by chemical/enzymatic breakdown of nucleic acids. often co-transmitters that modulate the release of other transmitters

adenosine

nucleoside formed from breakdown of adenine triphosphate (ATP). ATP is primary energy source so adenosine promotes sleep and suppresses arousal

• high firing postsynaptic firing rate at synapses where adenosine is primary neurotrans = sleepiness

caffine

naturally occuring nucleoside in plants and acts as adenosine-receptor antagonist. Increases alertness by reducing activation/firing of adenosine neurons

gas

air-like fluid substance that expands freely in any given space

• soluble gas = dissolve in liquid (dependent on pressure and temp)

2 gases that act as neurotransmitters

nitric oxide and carbon monoxide

nitric oxide

in brain produced from amino acid arginine in a subpopulation of 1-2% of neurons in cortex. exact function unclear

• involved in learning and memory due to effects synaptic plasticity

• dilates blood vessels in brain regions that are metabolically active

how is NO different to traditional neurotransmitters

• not synthesised and stored in vesicles - NO produced throuout cell including dendrites and defuse out as soon as produced

• doesn’t activate receptors - just enters neighbouring cells

• very short lived and is degraded or reacted within few seconds of being produced