Neonate Flashcards
What does fine tuning involve?
Separation of tactile and nociceptive afferent input to the spinal cord’s dorsal horn and the maturation of local and descending inhibitory circuitry
In the neonatal cord, the unrefined connectivity means
noxious stimulation does not produce the same activity in the neuronal circuitry as in the adult (Fitzgerald, 2005)
Why might pacemaker neurons be useful for nociceptive system development (who)?
The excitatory drive provided by pacemaker neurons may be beneficial by allowing spinal circuit refinement without requiring repeated noxious input from the periphery (Baccei, 2014) in the normal situation.
Why is spontaneous muscle activity important in nociceptive system development?
Creates skin movement that provides innocuous feedback to the developing dorsal horn, and may be involved in driving the refinement of ectopic A-beta fibres in the most superficial laminae, a necessary event for the normal development of the nociceptive withdrawal reflex. (Li et al.,2014)
How will changes to input affect dorsal horn neurons?
affect the electrophysiological properties of dorsal horn neurons, including pacemakers, reducing their intrinsic excitability into adulthood
pacemaker activity is highly responsive to sensory experience
What does descending faciliatory tone do in development?
In the neonate, the descending faciliatory tone on low-threshold afferent input will act to promote the ongoing activity-dependent development and refinement of dorsal horn nociceptive circuitry.
How is inhibitory tone developed?
Activity, in terms of sensory influence from the physical environment, provides tactile and noxious input in postnatal life and drives the maturation of high-threshold connectivity and synaptic transmission in the dorsal horn (in addition to endogenous pacemaker activity), which, in turn, drives glycinergic inhibitory maturation.
What are the implications of early injury?
- Endogenous spinal inhibitory tone is reduced and less effective - in humans potentially throughout childhood and into early adolescence
- The balance of descending facilitation and inhibition may be disrupted
What did investigation of EP individuals show (who)?
- Localized allodynia and hypersnsitization adjacent to neonatal scars
- Sex-dependent changes in amygdala volume which correlated with degree and directionality of thermal sensitivity
- Altered processing of the condition stimulus in conditioned pain modulation studies
- Subgroup of EP females that had reduced pain pressure threshold and cold-presser tolerance
How do animal studies demonstrate long term changes to dorsal horn circuitry following early injury (which researchers)?
Neonatal hindpaw inflammation induced by carrageenan leads to long-term alterations in supraspinal circuitry and enhanced inhibition from the RVM (Zhang et al.,2010)
+ alterations in opioid- mediated responses in the periaqueductal grey (Laprairie and Murphy, 2009)
What suggests early injury might affect persistent pain in humans (who)?
infant surgery in the same dermatome where prior neonatal surgery had taken place was associated with increased pain and perioperative analgesic requirements (Peters et al.,2005).
How could we mitigate against the risk of persistent pain?
Inhibiting microglia at the time of initial incision with pharmacological agents such as minocycline; this was found to prevent persistent mechanical and thermal hyperalgesia following secondary incision in adult male rats (Moriarty et al., 2019)
