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Modulation of parasympathetic neuron phenotype and function by sympathetic innervation
Peter G Smith1, J Donald Warn, Jena J Steinle
1Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City 66160-7401, USA. psmith@kumc.edu
Autonomic Neuroscience : Basic & Clinical
|March 26, 2002
Summary
Sympathetic nerve loss impairs parasympathetic function and alters neurotransmission in orbital tissues. Sympathetic activity is crucial for maintaining parasympathetic neuron health and function, partly via nerve growth factor (NGF).
Area of Science:
- Neuroscience
- Autonomic Nervous System Research
- Ocular Physiology
Background:
- Selective sympathetic nerve dysfunction is observed in aging and disease.
- The interplay between sympathetic and parasympathetic innervation is critical for target tissue function.
- Parasympathetic neurons innervate orbital structures, including vasculature and smooth muscle.
Purpose of the Study:
- To investigate the impact of chronic sympathetic denervation on parasympathetic innervation in adult rat orbital tissues.
- To elucidate the role of sympathetic neurotransmission in regulating parasympathetic neuron phenotype and function.
- To explore the potential mechanisms, including axo-axonal synapses and nerve growth factor (NGF), mediating sympathetic influences.
Main Methods:
- Surgical excision of the superior cervical ganglion to induce chronic sympathetic denervation in adult rats.
- Analysis of pterygopalatine ganglion parasympathetic neurons for nitric oxide synthase (NOS) protein and NGF expression (mRNA and protein).
- Laser Doppler measurements to assess ocular blood flow and nitrergic vasodilatation.
- Microscopic examination of parasympathetic varicosity apposition to smooth muscle cells in the superior tarsal muscle.
Main Results:
- Sympathetic denervation reduced nitric oxide synthase (NOS) protein in parasympathetic neurons and their projections.
- Reduced nitrergic vasodilatation was observed in ocular vasculature following sympathectomy.
- Parasympathetic varicosities proliferated and closely contacted smooth muscle cells in the superior tarsal muscle, enabling excitatory neurotransmission.
- Nerve growth factor (NGF) mRNA and protein levels were significantly reduced in parasympathetic neurons after chronic sympathectomy.
Conclusions:
- Parasympathetic neurons exhibit a marked dependency on sympathetic nerves for maintaining normal phenotype and function.
- Sympathetic influences on parasympathetic neurons may involve axo-axonal synapses.
- Sympathetic neurotransmission enhances NGF expression in parasympathetic neurons, potentially reinforcing their structural and functional associations.