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Cotransmitter-mediated locus coeruleus action on motoneurons
S I Fung1, J Y Chan, D Manzoni
1Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman 99163-6520.
Brain Research Bulletin
|January 1, 1994
Summary
A direct noradrenergic pathway from the dorsolateral pontine tegmentum (DLPT) to spinal motoneurons exists. This pathway utilizes norepinephrine (NE), glutamate (Glu), and enkephalin (ENK) as cotransmitters, influencing motoneuron responses and reflex activity.
Area of Science:
- Neuroscience
- Neuroanatomy
- Neurophysiology
Background:
- The dorsolateral pontine tegmentum (DLPT) is known to project to spinal motoneurons.
- Previous studies suggested a noradrenergic projection from the locus coeruleus (LC) within the DLPT to spinal cord.
- The precise neurotransmitters and their roles in this pathway were not fully elucidated.
Purpose of the Study:
- To review and synthesize evidence for a direct noradrenergic projection from the DLPT to spinal motoneurons.
- To investigate the potential roles of glutamate (Glu) and enkephalin (ENK) as cotransmitters with norepinephrine (NE) in this pathway.
- To understand the functional implications of this heterogeneous neurotransmission on motoneuron activity and spinal reflexes.
Main Methods:
- Anatomical studies combining retrograde tracing and immunohistochemistry to identify neurotransmitters in DLPT neurons projecting to the spinal cord.
- Electrophysiological recordings of spinal motoneuron responses to DLPT stimulation.
- Pharmacological analysis using adrenergic, glutamatergic, and enkephalinergic antagonists to determine the contribution of each neurotransmitter.
- Assessment of effects on lumbar monosynaptic reflex (MSR) amplitude.
Main Results:
- Confirmed a direct noradrenergic pathway from the LC and adjacent DLPT to the lumbar ventral horn.
- Identified colocalization of glutamate (Glu) or enkephalin (ENK) in many noradrenergic DLPT neurons projecting to the spinal cord.
- Demonstrated that DLPT stimulation evokes a complex depolarization in motoneurons, only partially mediated by NE.
- Showed that Glu contributes to the excitatory component, while ENK mediates the inhibitory component of DLPT's effect on spinal reflexes.
Conclusions:
- The DLPT exerts a modulatory influence on spinal motoneurons through a direct pathway involving NE, Glu, and ENK.
- The colocalization and differential roles of these neurotransmitters contribute to the diverse postsynaptic potentials observed in motoneurons.
- This chemically heterogeneous system provides a mechanism for complex regulation of motor output.