|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
Effects of Nicotinic and Muscarinic Agents on an Identified Motoneurone and its Direct Afferent Inputs in Larval Manduca Sexta
1 Department of Entomological Sciences, University of California, Berkeley, CA 94720, USA; Department of Biology, Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA
The principal locomotory appendages of larval Manduca sexta, the prolegs, bear at their tips an array of mechanosensory hairs (the planta hairs). Each of the single sensory neurones associated with a planta hair sends an axon into the ganglion of the same segment where the afferent terminals make synaptic contact with interneurones and motoneurones. Electrical stimulation of a single afferent elicits a monosynaptic excitatory postsynaptic potential (EPSP) in PPR, one of the motoneurones controlling the prolegs. We have used this synapse to study the pharmacology of sensory transmission in M. sexta. The following observations were made.
1. The EPSP was reversibly inhibited in a dose-dependent fashion by the cholinergic antagonists d-tubocurarine, atropine and mecamylamine, indicating that the planta hair afferent neurones use acetylcholine (ACh) as a neurotransmitter. 
-Bungarotoxin (BGTX) also suppressed the EPSP but required concentrations above 1x10-6mol l-1.
2. PPR depolarized in response to ionophoretic or bath application of cholinergic agonists, but compared to motoneurones of a non-nicotine-resistant insect such as the cockroach, PPR was relatively insensitive to nicotine.
3. Application of N-methyl nicotinamide (NMN) to the nerve cord to inhibit putative alkaloid pumps in the central nervous system (CNS) only weakly potentiated PPR's response to nicotine. This suggests that such pumps do not markedly contribute to PPR's nicotine resistance.
4. PPR's responses to nicotinic agents showed several pharmacological differences from those reported for other insects, indicating that the nicotinic ACh receptors of M. sexta may be specifically adapted to accommodate a nicotine-rich diet.
5. During the application of muscarinic agonists to isolated abdominal ganglia, the firing rate of motoneurones, as monitored in the ventral nerve, increased dramatically. PPR responded to muscarinic agents even during synaptic blockade, suggesting that muscarinic receptors may be present on PPR itself. The main effect of muscarine on PPR was to lower its spike threshold.
6. Bath-applied muscarinic agents also affected the afferent-evoked EPSP in a manner consistent with the presence of another group of receptors that, when stimulated, act presynaptically to inhibit the release of ACh from the sensory terminals.
These apparent pre- and postsynaptic actions of muscarinic agents are the first reported findings of muscarinic physiology in an identified insect neurone and its synaptic inputs.
Key words: Manduca sexta, insect CNS, cholinergic receptors, nicotine, muscarinic
Accepted on March 13, 1989
This article has been cited by other articles:
|
|
 |
|
  J. E. Bestman and R. Booker The control of anterior foregut motility during a larval molt of the moth Manduca sexta involves the modulation of presynaptic activity J. Exp. Biol., October 15, 2006; 209(20): 4000 - 4010. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Ismail, G. E. Robinson, and S. E. Fahrbach Stimulation of muscarinic receptors mimics experience-dependent plasticity in the honey bee brain PNAS, January 3, 2006; 103(1): 207 - 211. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Mezoff, N. Papastathis, A. Takesian, and B. A. Trimmer The biomechanical and neural control of hydrostatic limb movements in Manduca sexta J. Exp. Biol., September 1, 2004; 207(17): 3043 - 3053. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. E. Bestman and R. Booker Modulation of foregut synaptic activity controls resorption of molting fluid during larval molts of the moth Manduca sexta J. Exp. Biol., April 1, 2003; 206(7): 1207 - 1220. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. R. Gray and J. C. Weeks Steroid-Induced Dendritic Regression Reduces Anatomical Contacts between Neurons during Synaptic Weakening and the Developmental Loss of a Behavior J. Neurosci., February 15, 2003; 23(4): 1406 - 1415. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Fuse and J. W. Truman Modulation of ecdysis in the moth Manduca sexta: the roles of the suboesophageal and thoracic ganglia J. Exp. Biol., April 15, 2002; 205(8): 1047 - 1058. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Wenzel, N. Elsner, and R. Heinrich mAChRs in the Grasshopper Brain Mediate Excitation by Activation of the AC/PKA and the PLC Second-Messenger Pathways J Neurophysiol, February 1, 2002; 87(2): 876 - 888. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Champlin and J. Truman Ecdysteroid coordinates optic lobe neurogenesis via a nitric oxide signaling pathway Development, January 8, 2000; 127(16): 3543 - 3551. [Abstract] [PDF]
|
|
|
|
|
|
B Wenzel and B Hedwig Neurochemical control of cricket stridulation revealed by pharmacological microinjections into the brain J. Exp. Biol., January 8, 1999; 202(16): 2203 - 2216. [Abstract] [PDF]
|
|
|
|
|
|
S. Gammie and J. Truman Eclosion hormone provides a link between ecdysis-triggering hormone and crustacean cardioactive peptide in the neuroendocrine cascade that controls ecdysis behavior J. Exp. Biol., January 2, 1999; 202(4): 343 - 352. [Abstract] [PDF]
|
|
|
|
|
|
C. Consoulas and R. B. Levine Presynaptic Function during Muscle Remodeling in Insect Metamorphosis J. Neurosci., August 1, 1998; 18(15): 5817 - 5831. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. C. Gammie and J. W. Truman Neuropeptide Hierarchies and the Activation of Sequential Motor Behaviors in the Hawkmoth, Manduca sexta J. Neurosci., June 1, 1997; 17(11): 4389 - 4397. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Nagayama, H. Aonuma, and P. L. Newland Convergent Chemical and Electrical Synaptic Inputs From Proprioceptive Afferents Onto an Identified Intersegmental Interneuron in the Crayfish J Neurophysiol, May 1, 1997; 77(5): 2826 - 2830. [Abstract] [Full Text] [PDF]
|
|
