Effects of cholinergic and noradrenergic agents on locomotion in the mudpuppy (Necturus maculatus)

• Published in: Experimental brain research 2002-08, Vol.145 (4), p.498-504
• Main Authors: FOK, M, STEIN, R. B
• Format: Article
• Language: English
• Subjects: Acetylcholine - metabolism; Adrenergic alpha-Agonists; Animals; Atropine - pharmacology; Biological and medical sciences; Carbachol - pharmacology; central pattern generator; Cholinergic Agonists - pharmacology; Cholinesterase Inhibitors - pharmacology; Clonidine - pharmacology; Excitatory Amino Acid Agonists - pharmacology; Fundamental and applied biological sciences. Psychology; Interneurons - drug effects; Interneurons - metabolism; Locomotion - drug effects; Locomotion - physiology; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Motor Neurons - drug effects; Motor Neurons - metabolism; Muscarinic Antagonists; N-Methylaspartate - pharmacology; Necturus maculatus; Necturus maculosus; Nerve Net - drug effects; Nerve Net - metabolism; Norepinephrine - metabolism; Physostigmine - pharmacology; Rhythm; Spinal cord; Spinal Cord - drug effects; Spinal Cord - metabolism; Vertebrates: nervous system and sense organs
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s00221-002-1125-6

Some neurotransmitters act consistently on the central pattern generator (CPG) for locomotion in a wide range of vertebrates. In contrast, acetylcholine (ACh) and noradrenaline (NA) have various effects on locomotion in different preparations. The roles of ACh and NA have not been studied in amphibian walking, so we examined their effects in an isolated spinal cord preparation of the mudpuppy ( Necturus maculatus). This preparation contains a CPG that produces locomotor activity when N-methyl- D-aspartic acid (NMDA), an excitatory amino acid agonist, is added to the bath. The addition of carbachol, a long acting ACh agonist, to the bath disrupted the walking rhythm induced by NMDA, while not changing the level of activity in flexor and extensor motoneurons. Adding clonidine, an alpha(2)-noradrenergic agonist, had no effect on the NMDA-induced walking rhythm. Physostigmine, an ACh-esterase inhibitor, disrupted the walking rhythm, presumably by potentiating the effects of endogenously released ACh. Atropine, an ACh antagonist that binds to muscarinic ACh receptors, blocked the effects of carbachol, indicating that the action is mediated, at least in part, by muscarinic receptors. In the absence of carbachol, atropine had no effect. Locomotion was not induced by carbachol, atropine or clonidine in a resting spinal cord preparation. Cholinergic actions do not seem to be essential to the CPG for walking in the mudpuppy, but ACh may convert a rhythmic walking state to a more tonic state with occasional bursts of EMG activity for postural adjustments.