Responses of efferent octopaminergic thoracic unpaired median neurons in the locust to visual and mechanosensory signals.
Insect thoracic ganglia contain efferent octopaminergic unpaired median neurons (UM neurons) located in the midline, projecting bilaterally and modulating neuromuscular transmission, muscle contraction kinetics, sensory sensitivity and muscle metabolism. In locusts, these neurons are located dorsally or ventrally (DUM- or VUM-neurons) and divided into functionally different sub-populations activated during different motor tasks. This study addresses the responsiveness of locust thoracic DUM neurons to various sensory stimuli. Two classes of sense organs, cuticular exteroreceptor mechanosensilla (tactile hairs and campaniform sensilla), and photoreceptors (compound eyes and ocelli) elicited excitatory reflex responses. Chordotonal organ joint receptors caused no responses. The tympanal organ (Müller's organ) elicited weak excitatory responses most likely via generally increased network activity due to increased arousal. Vibratory stimuli to the hind leg subgenual organ never elicited responses. Whereas DUM neurons innervating wing muscles are not very responsive to sensory stimulation, those innervating leg and other muscles are very responsive to stimulation of exteroreceptors and hardly responsive to stimulation of proprioceptors. After cutting both cervical connectives all mechanosensory excitation is lost, even for sensory inputs from the abdomen. This suggests that, in contrast to motor neurons, the sensory inputs to octopaminergic efferent neuromodulatory cells are pre-processed in the suboesophageal ganglion.
Field
Laurence H
LH
School of Biological Sciences, University of Canterbury, PB4800 Christchurch, New Zealand. larry.field@canterbury.ac.nz
Duch
Carsten
C
Pflüger
Hans-Joachim
HJ
D000818:Animals; D017952:Ganglia, Invertebrate / Q000502:physiology*; D006110:Grasshoppers / Q000502:physiology*; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D009476:Neurons, Efferent / Q000378:metabolism*; D010812:Physical Stimulation; D017982:Receptors, Biogenic Amine / Q000378:metabolism*; D013997:Time Factors; D014785:Vision, Ocular / Q000502:physiology*
D017982:Receptors, Biogenic Amine; C027604:norsynephrine receptor