Other messengers: histamine, opioids, hormones and more
Rounds out the messengers you'll meet as side effects and drug targets: histamine, opioid peptides, hormones, endocannabinoids and adenosine.
Where this fitsConnects to 2 · Unlocks 1
- Connects to
- Primary effects and side effects — Antihistamine drowsiness is a classic predictable side effect.
- Acetylcholine: nicotinic, muscarinic and AChE — Diphenhydramine also blocks muscarinic receptors.
- Unlocks
- Absorption and routes of administration — Opioid examples reappear: fentanyl patches, naloxone, buprenorphine/naloxone.
Orient
Other messengers: histamine (first-generation antihistamines cause drowsiness by blocking H1 receptors in brain), opioid peptides (endorphins and enkephalins; mu receptor focus of opiate drugs), hormones – released from glands for wider circulation (not just within synapse), such as oxytocin and melatonin – plus endocannabinoids and adenosine.
Course terms
Your professor's wording, word for word from the slides. Learn the term and this definition — the explanation underneath is only there to help it make sense.
- First-generation antihistamines
“First-generation antihistamines tend to cause drowsiness as a major side effect; H1 receptors in brain”Slides 03, p. 40
Benadryl (diphenhydramine) is a first-generation antihistamine, with anticholinergic action at muscarinic receptors too.
- Second-generation antihistamines
“Second-generation antihistamines (Claritin; Zyrtec) don’t have action at H1 receptors in brain = no drowsiness”Slides 03, p. 40
Same target, but they stay out of the brain.
- Opioid peptides
“Endorphins and enkephalins”Slides 03, p. 42
Larger proteins; act at mu, kappa and delta receptors.
- Mu receptor
“Mu receptor focus of opiate drugs”Slides 03, p. 42
Effects summed up as “CHARMED by opioids”.
- CHARMED
“Constipation Habit-forming Analgesia Respiratory depression Miosis Euphoria Drowsiness”Slides 03, p. 42
The mu-opioid effects mnemonic.
- Hormone
“Released from glands for wider circulation (not just within synapse)”Slides 03, p. 43
Why oxytocin and melatonin are hormones, not neurotransmitters; hormones can also bind intracellular receptors.
- Melatonin
“Sleep-inducing hormone, released in accordance with circadian rhythm”Slides 03, p. 43
Binds MT receptors. Endogenous — the body makes it.
- Oxytocin
“Labor contractions and breastfeeding”Slides 03, p. 43
Binds OXTR; role in social bonding — the “love” hormone.
- Endocannabinoids
“Modulate and regulate other NT release when produced and released (primarily presynaptic)”Slides 03, p. 44
Named after cannabis, whose chemicals were documented first.
- Adenosine
“Byproduct of metabolic reactions; accumulated when expending energy (ATP)”Slides 03, p. 44
Role in sleep and wakefulness; inhibitory.
From your course: Course slides 03, pp. 40–44
Tip: the ← and → keys move through the lesson.
Full lesson: Histamine, peptides and other messengers