Dorsal unpaired median insect neurons make neurosecretory endings on skeletal muscle

Abstract

This report presents r e s u l t s of a study in Schistocerca gregaria of large dorsal unpaired median neurons found p r e v i o u s 5 in ganglia of several insects (Crossman e t a l . , '71a; Hoyle, unpublished). Most of these neurons give off a single median neurite t h a t makes a T-branch, providing symmetrical l e f t and r i g h t e f f e r e n t axons. These axons emerge i n ganglion nerve trunks and terminate in each of two nerves. They then travel t o major skeletal leg muscles. One of the neurons supplies only the extensor t i b i a e ( j u m p i n g muscle).The f i n a l branches of t h i s neuron parallel the f a s t axon and supply muscle units t h a t receive the f a s t axon only. All the muscle f i b e r s in a unit a r e innervated (multiterminally) by the f a s t axon, b u t only a few receive terminals of the dorsal neuron i n addition. The endings a r e of neurosecretory type, containing large numbers of dense core vesicles. Their function i s unknown.I n 1971, Crossman e t al. ( ' 7 1 a ) reported large nerve cell bodies in the mid-lines of the dorsal surfaces of cockroach and locust thoracic ganglia t h a t give large, overshooting action potentials. Each neuron makes a T-branch, the arms o f which are symmetrical, l e f t and right neurites.forms axons t h a t emerge from ganglion nerve trunks. appear t o be e f f e r e n t neurons supplying muscles, although t h e i r i d e n t i t y could not be ascertained. Each of these branchesThe large dorsal c e l l s thusIn both cockroach and locust, Crossman e t a l . ( ' 7 2 ) consistently found eight o f these neurons, apparently a l l identical and with similar branching patterns.In t h e i r f i r s t detailed account Crossman e t a l . ( ' 7 l a ) , showed the neuron as having b u t a single pair of o u t p u t s , in N5 (designation of Pringle, '39). In a 159

Co-Contraction and Passive Forces Facilitate Load Compensation of Aimed Limb Movements

“…Its pennate muscle fibers are innervated by only four motoneurons: the excitatory fast (FETi) and slow (SETi) extensor tibiae neurons, a common inhibitor (CI1) (Hoyle, 1955a,b;Usherwood and Grundfest, 1965), and a modulatory dorsal unpaired median neuron (Hoyle et al, 1974;Bräunig and Pflüger, 2001). Individual muscle fibers are innervated in 1 of 12 neuron combinations (Hoyle, 1978).…”

A modulatory octopaminergic neurone increases cyclic nucleotide levels in locust skeletal muscle.

“…Where possible, the contralateral leg was used as a control. The octopamine-containing neurone to the extensor-tibiae muscle has been designated DUMETi (Dorsal Unpaired Median cell to Extensor Tibiae muscle) (Hoyle et al 1974). DUMETi was stimulated antidromically by a pair of hook electrodes placed on the contralateral extensor tibiae nerve (5b,: nomenclature of Pringle, 1939).…”

“…A single octopamine-containing neurone modulates neuromuscular transmission (Evans & O'Shea, 1977;O'Shea & Evans, 1979;Evans, 1982) and various forms of muscle tension (Hoyle, 1975;Evans & O'Shea, 1978;Evans & Siegler, 1982). The neurone is unpaired in the central nervous system and its axon bifurcates into symmetrical branches that innervate the extensor tibiae muscle in both the right and left legs of the locust (Hoyle, Dagan, Moberly & Colquhoun, 1974). It can be easily identified physiologically and selectively stimulated (see Evans & O'Shea, 1978), as can the three motoneurones that innervate each extensor tibiae muscle.…”

Electrical excitability: A spectrum of properties in the progeny of a single embryonic neuroblast

“…Our studies thus far have sought to describe the temporal pattern of differentiation from an identified neuroblast (precursor cell) to a group of identified neurons. Each thoracic segment in the embryo contains over 60 precursor cells that give rise to the roughly 3000 neurons of each thoracic ganglion (5). The subjects of our studies have been the dorsal unpaired median (DUM) neurons, whose t100 somata form a distinct cluster on the dorsal midline of each segmental ganglion (6)(7)(8). A single embryonic precursor cell, the median or DUM neuroblist, gives rise to most of the DUM neurons (1); two of them are the progeny of another precursor cell, MP3 (3,4).…”