Background & Aims

In the neonate, nociceptive behaviour is initially observed as a widespread and uncoordinated reflex, which gradually matures to be both site-specific and precise in nature. Similarly in the mouse, the refinement of the nociceptive behaviour begins at the end of the first postnatal week. This maturation coincides with the strengthening of the C-fibre inputs and the consequent decrease of tactile A-fibre evoked excitability in the superficial layers of dorsal horn throughout the second week (1). While it is established that sensory inputs from the periphery play a crucial role in the maturation of nociceptive reflexes, the impact of modified early-life peripheral experiences on the typical development of these circuitries remains unclear. The present study aims to establish the functional impact of increased early life TRPV1-fibre nociceptive inputs upon the maturation of somatosensory and nociceptive behaviours.

Methods

To genetically control primary nociceptive afferent activity in vivo, newborn (P0, post-natal day 0) TRPV1-Cre transgenic mice received an intraplantar injection of the Cre-inducible adeno-associated viral vector coding for the excitatory hM3Dq DREADD or the respective control virus. Following this, mice were randomly arranged in two groups to receive intraperitoneal injections (twice a day) of the DREADD ligand clozapine-N-oxide (CNO, 5 mg/kg) at one of two critical developmental periods: P8-P12 and P13-P17. After reaching adulthood, sensory-evoked behaviour of the hindlimb was tested using a battery of innocuous (brush, Von Frey) and noxious (pin prick, hotplate, acetone) tests. Fine limb motor coordination and balance were assessed using a gait analysis system for rodents (CatWalk XT) and the beam walking assay. Kinematics were analysed using the marker less pose estimation software SLEAP (2).

Results

The temporally regulated activation of TRPV1-positive fibres during the developmental window of P8-P12 induced alterations in the response to innocuous stimuli, such as brushing, whilst the progression of sensorimotor behaviours remained unaltered. In contrast, activation of TRPV1-positive fibres at the critical period of P13-P17 resulted in pronounced sensory-motor deficits. Notably, this aberrant activation did not affect somatosensory-driven behaviour. Lastly, immunohistochemical analysis of lumbar spinal cord tissue from the P13-P17 group revealed an increase in both density and spread of CGRP-positive nociceptive afferent terminals toward the deepest layers of the dorsal horn region.

Conclusions

These results indicate that activation of peripheral TRPV1 positive afferents can recruit two separate motor programs over development, depending upon the timing of the activation, suggesting a cross-modal maturation of sensorimotor circuits.

References

1. Jennings E. & Fitzgerald M., Journal of Physiology (1998).
2. Pereira T.D., et al.,?Nat Methods (2022).
3. Fitzgerald M. & Walker S.M., Nature Reviews Neurology (2009).

Presenting Author

Laura Andreoli

Poster Authors

Laura Andreoli

PhD

UCL

Lead Author

E-mail

Topics

  • Mechanisms: Biological-Molecular and Cell Biology