Opioid-induced depression in the lamprey respiratory network

Area of Science:

• Neuroscience
• Comparative Physiology
• Respiratory Control

Background:

• Opioid receptors are known to influence vital functions, including respiration, in various species.
• The specific role of different opioid receptor subtypes in respiratory control across vertebrate evolution remains incompletely understood.

Purpose of the Study:

• To investigate the role of opioid receptors in modulating respiratory activity in the primitive vertebrate, the lamprey.
• To identify specific opioid receptor subtypes and brain regions involved in respiratory rhythmogenesis.

Main Methods:

• In vitro brainstem preparations of adult lampreys were used to study respiratory activity via vagal motor output.
• Opioid receptor agonists (DAMGO, DPDPE, U50488) and antagonists (naloxone, naltrindole) were applied via bath or microinjections.
• Neuronal recordings were performed in the rostrolateral trigeminal region.

Main Results:

• Bath application of the micro-opioid receptor agonist DAMGO markedly decreased respiratory frequency, leading to apnea.
• Delta-opioid receptor agonist DPDPE had less pronounced depressant effects, while kappa-opioid receptor agonist U50488 had no effect.
• Microinjections of DAMGO into the paratrigeminal respiratory group (pTRG) abolished the respiratory rhythm.
• Opioid receptor antagonists prevented agonist-induced respiratory depression but did not affect baseline activity.

Conclusions:

• Micro-opioid receptor activation plays a critical role in respiratory depression in lampreys.
• A specific opioid-sensitive region, the pTRG, is pivotal for respiratory rhythmogenesis.
• The inhibitory effect of opioids on respiration is an evolutionarily conserved trait present early in vertebrate evolution.