Cognitive, Behavioral, and Systems NeuroscienceResearch PaperThe time course of serotonin 2A receptor expression after spinal transection of rats: an immunohistochemical study
Graphical Abstract
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Research highlights
▶5-HT2A receptor expression was investigated in spinalized rats at 7 time points. ▶5-HT2A receptor started to upregulate in spinal motoneurons 1 day after lesion. ▶5-HT2A receptor upregulation reached a plateau level at around 28 days. ▶5-HT2A receptor upregulation is implicated in 5-HT denervation supersensitivity.
Section snippets
Animal operation and tissue preparations
All experiments were conducted in accordance with the guidelines of the EU Directive 86/609/EEC and were approved by the Danish Animal Experiments Inspectorate. All efforts were made to minimize the number of animals used and their suffering. Initially a total of 132 adult male Wistar rats were used with a body weight of 200–250 g. Due to the loss of animals during the post-operative period and the exclusion of those animals with incorrect lesion sites 117 remaining rats were used in this study
Spinal lesion sites in the spinalized rats
In most cases, especially in those with a long post-operation survival time, it could be confirmed by surgical microscope that the spinal cord was completely transected at S2–S3 spinal segments, where a 2–3 mm space could be clearly observed between the rostral and the caudal stumps (Fig. 1A, B). In the cases whose spinal transection sites were processed with Fast Blue and Thionin the results showed that all of the spinal cords were completely transected with no neurons or nerve fibers passing
Discussion
Using immunohistochemistry our present study has revealed the time course of 5-HT2AR expression changes following a complete spinal transection. We have demonstrated that 5-HT2AR upregulation starts at a time point before 1 day after spinalization and reaches a plateau at approximately the fourth week. Our previous findings have demonstrated that this upregulation persists for at least 2 months—the longest time we have investigated so far (Kong et al., 2010). We also investigated the changes of
Conclusion
In this study we have shown that 1 day after spinalization the levels of 5-HT2AR-IR increased in the motoneuron somata and their dendrites and this increase persisted for an indefinite long period. Furthermore, the time course of 5-HT2AR upregulation was significantly correlated with the development of 5-HT denervation supersensitivity. These results indicate that the upregulation of 5-HT2ARs at least partly underlies the development of 5-HT denervation supersensitivity in spinal motoneurons
Acknowledgments
We are grateful to Lillian Grøndahl for her unfailing assistance in all phases of this investigation. We thank Dr. Claire Meehan for critical reading of the manuscript. This project was supported by the Lundbeck Foundation, the Danish Multiple Sclerosis Foundation, the Ludvig and Sara Elsass' Foundation, Sofus Friis Foundation and the Danish Medical Research Council.
References (53)
- et al.
The effect of 5-HTP on the static fusimotor activity and the tonic stretch reflex of an extensor muscle
Brain Res
(1971) - et al.
Long-lasting recovery of locomotor function in chronic spinal rat following chronic combined pharmacological stimulation of serotonergic receptors with 8-OHDPAT and quipazine
Neurosci Lett
(2005) - et al.
Denervation supersensitivity to 5-hydroxytryptophan in rats following spinal transection and 5,7-dihydroxytryptamine injection
Neuropharmacology
(1981) - et al.
Distribution of serotonin 2A and 2C receptor mRNA expression in the cervical ventral horn and phrenic motoneurons following spinal cord hemisection
Exp Neurol
(2001) - et al.
Progressive increase of motor activity induced by 5-HTP in the rat below a complete section of the spinal cord
Brain Res
(1979) - et al.
Possible functions of transmitter-controlled plateau potentials in alpha motoneurones
Prog Brain Res
(1989) - et al.
Serotonin and l-norepinephrine as mediators of altered excitability in neonatal rat motoneurons studied in vitro
Neuroscience
(1992) - et al.
Use of serotonin immunocytochemistry as a marker of injury severity after experimental spinal trauma in rats
Brain Res
(1988) The mammalian central pattern generator for locomotion
Brain Res Rev
(2009)- et al.
Spinal cord serotonin: a biochemical and immunohistochemical study following transection
Brain Res
(1984)
Changes in serotonin, serotonin transporter expression and serotonin denervation supersensitivity: involvement in chronic central pain after spinal hemisection in the rat
Exp Neurol
5-HT precursor loading, but not 5-HT receptor agonists, increases motor function after spinal cord contusion in adult rats
Exp Neurol
Robust upregulation of serotonin 2A receptors after chronic spinal transection of rats: an immunohistochemical study
Brain Res
Up-regulation of 5-HT2 receptors is involved in the increased H-reflex amplitude after contusive spinal cord injury
Exp Neurol
The morphology and distribution of rat serotoninergic intraspinal neurons: an immunohistochemical study
Brain Res Bull
The role of serotonin in reflex modulation and locomotor rhythm production in the mammalian spinal cord
Brain Res Bull
Distribution of serotonin-immunoreactivity in the central nervous system of the rat-cell bodies and terminals
Neuroscience
The time course of the disappearance of noradrenaline and 5-hydroxytryptamine in the spinal cord after transection
Acta Physiol Scand
Locomotor recovery in the chronic spinal rat: effects of long-term treatment with a 5-HT2 agonist
Eur J Neurosci
Action of cyproheptadine in spastic paraparetic patients
J Neurol Neurosurg Psychiatry
Spasticity in rats with sacral spinal cord injury
J Neurotrauma
Evidence for plateau potentials in tail motoneurons of awake chronic spinal rats with spasticity
J Neurophysiol
Plateau potentials in sacrocaudal motoneurons of chronic spinal rats, recorded in vitro
J Neurophysiol
Spastic long-lasting reflexes in the awake rat after sacral spinal cord injury
J Neurophysiol
Molecular physiology of norepinephrine and serotonin transporters
J Exp Biol
Down-regulation of the potassium-chloride cotransporter KCC2 contributes to spasticity after spinal cord injury
Nat Med
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