Chemical anatomy of pain pathways 2.3 Flashcards
Q: What are the two main aims when discussing the ascending and descending pathways in relation to noxious stimuli transmission?
A: To describe the features of ascending nociceptive pathways, and illustrate the neurochemical heterogeneity of descending pathways.
Q: Where are most projection neurons found in the spinal cord?
A: Most projection neurons are found in laminae I and V of the spinal cord.
Q: What are the two main ascending pathways from the spinal cord dorsal horn?
A: The two main tracts are the spinothalamic pathway and the spinoparabrachial pathway.
Q: What is the role of the spinothalamic and spinoparabrachial pathways?
A: The spinothalamic pathway carries sensory-discriminative information to the contralateral thalamus, while the spinoparabrachial pathway transmits information to the parabrachial nuclei and from there to limbic system circuits like the amygdala and insular cortex, contributing to the emotional aspect of pain.
Q: What types of neurons are found in Lamina I, III, and V?
A: Lamina I contains largely nociceptive-specific neurons, while Laminae III and V contain mostly WDR (wide-dynamic-range) projection neurons.
Q: What is the role of WDR neurons in the spinal cord?
A: WDR projection neurons receive inputs from Lam II interneurons and A-beta fibers, responding to both noxious and innocuous stimuli.
Q: Are projection neurons inhibitory or excitatory?
A: All projection neurons are thought to be excitatory, none express GABA or glycine.
Q: What percentage of Lamina I neurons in rodents project to the Parabrachial nucleus?
A: 80% of Lamina I neurons project to the Parabrachial nucleus.
Q: What methods are being used to better understand projection neuron subpopulations?
A: Transcriptomics and modern tools like optogenetics are being used to create molecular and functional databases of projection neurons.
Q: What was the finding in the study by Wang et al. regarding TRPV1 and Mrgprd+ neurons?
A: In optogenetic experiments, only stimulation of TRPV1 positive neurons elicited an affective behavioral response, indicating their role in the perception of pain, unlike Mrgprd+ neurons.
Q: What is the primary role of descending modulatory pathways?
A: Descending pathways modulate nociceptive information by either inhibiting or facilitating the transmission of pain signals.
Q: What neurotransmitters are involved in both descending inhibitory and facilitatory pathways?
A: 5-HT (serotonin), noradrenaline, and dopamine are present in both inhibitory and facilitatory pathways.
Q: What was the surprising finding of the study by Francois et al. on a GABAergic descending pathway?
A: They found that stimulation of GABAergic neurons in the RVM, which was expected to inhibit nociceptive transmission, actually facilitated mechanical nociception.
