The natural insect neuromodulator octopamine (OCT) was released iontophoretically into regions of neuropil in locust metathoracic ganglia. A narrowly-defined site was found on one side of the ganglion at which release caused a prolonged bout of repetitive flex-extend-flex movements of the tibia on the injected side, at a frequency of from 2-3.5 Hz. When a bout had terminated, repetition of the OCT release caused an extremely similar bout to occur, and again with further treatments, indefinitely. OCT iontophoresis at the equivalent site on the contralateral side caused the contralateral flexor to make stepping movements. Two sites were found, in each half of the ganglion, at which similar OCT release evoked a bout of flight motor activity at 10 Hz. The flight bout involved both sides synchronously and nearly equally, except for a slightly greater motor output on the injected side. Evoked bouts lasted from 20 sec to 25 min depending on the preparation and amount of OCT released. At a site in the 6th abdominal ganglion of mature female locusts OCT release suppressed ongoing rhythmic oviposition digging evoked by severing the ventral nerve cord. A number of previously undescribed DUM neurons was encountered and their dendritic patterns, which are distinctive, determined following dye injection. A hypothesis, termed the Orchestration Hypothesis is presented, which considers how modulator neurons such as locust octopaminergic neurons, might be involved in the generation of specific behaviors.

SUMMARYA preparation of the desert locust, Schistocera gregaria, has been developed, in which it was possible to work with identified neurons while still allowing some behavior. A total of 26 motorneurons to the hind leg were studied singly, and in various pairs, both by direct stimulation, and by recording during spontaneous activity and various reflex actions. Motorneurons were identified by passing current into their somata and correlating the evoked somata spikes with extracellularly or intracellularly recorded events in the muscles. Tension of the muscle was also recorded and motor axons were stimulated to evoke antidromic spikes in the somata. Both epsp's and ipsp's can be seen clearly in recordings from the somata; spikes appear as electrotonically conducted remnants only. Somata exhibited little or no electrogenesis. It is inferred that impulses are initiated in a zone tentatively identified with the region of emergence of the motor axon from the neuropil. Integration occurs in the neuropilar segment, with the soma serving as a parallel RC element. Data was obtained on the central mechanisms of coordination of synergistic and antagonistic motorneurons and on the modes of excitation of slow and fast neurons to the same muscles.

An account is presented of the brain (paired cerebral, pleural, and pedal ganglia) of the nudibranch mollusc Tritonia diomedia. The major efferent nerve fibers are related to their nerve cell bodies and their functional roles identified as far as possible. The channels of sensory input relating to some of these neurons are given so as to provide an overall view of the organization of the brain.A standardized system of abbreviation and notation for the central ganglia, nerve trunks, and giant somata is propcsed. The system of reference is intended to provide a guide to the location in the ganglia of many of the smaller neurons of which the functional attributes are known, but which cannot be consistently recognized on visual criteria alone. A system of rectangular coordinates is proposed which is applied to the natural outline of the ganglia. I n addition, a system of cell notation is described which is independent of the co-ordinates used to define the position of the cell on the grid. Cells which by reason of their size, pigmentation, characteristic location and physiological attributes are consistently recognizable from animal to animal are numbered. Two principles were followed in numbering cells; (i) the series begins at unity in each ganglion; (ii) cell homologues in opposite ganglia are given the same number, but distinguished by prefixing the abbreviation for the ganglion in which they occur. It is considered that the system will facilitate the exchange of information between workers on the same species, and also benefit the comparison of neural organization of behavior in closely related forms. The brain is organized in an almost exactly bilaterally symmetrical manner. There are a few bilateral neural pathways, but the major functional routes are ipsilateral. A few motorneurons, which are uniquely identifiable anatomically, cause unique, discrete movements. Others are in small groups sharing overlapping or similar functions.

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The musculature of the Onychophoran Peripatus dominicae , its ultrastructure and details of innervation are described. Significant differences were noted between its gross anatomy and that reported in previous accounts, notably in the presence of inner circular body wall muscle and a prominent, functionally significant, levator of the leg. The former is important in regard to the evolutionary position of the Onychophora while the latter helps us to understand the control of walking in a lobopodial leg, and therefore the evolution of arthropod locomotion, which was the focus of our interest. Individual muscle fibres are either directly or indirectly attached to the body wall by collagen. There is a small degree of branching of fibres, with or without anastomosis, near their insertions, but most are as long as the muscle of which they are part, and are unbranched except for an occasional thin arm, emerging at an angle, that becomes invaded by collagen fibres and inserts in the skin. Diameters of muscle fibres vary from 1 to 45 pm. They are invaginated by two separate systems of unique wide (0.3 pm) tubules, longitudinal and radial. These are lined with similar material to that forming the basement material of the sarcolemma, and also contain fine strands with collagen-type cross-banding that connect to collagen bundles outside the fibres. In addition there are narrow tubules of ordinary T-tubule diameter. Both wide and narrow tubules make contacts with sarcoplasmic reticulum cysternae. Dense Z bodies are attached to both kinds of wide tubule, to the inside of the sarcolemma, and are scattered, without any obvious array, in the sarcoplasm. Thin myofilaments emerge from the Z bodies parallel to the fibre axis. Thick filaments occur in clusters with a loosely hexagonal array, but without any regular relation to thin ones: relatively few orbits of thin around thick filaments were seen in many muscle fibres regardless of fibre length and conditions during fixation. A unique innervation pattern was found, consisting of a combination of muscle arm to nerve contacts, which appear to be the commonest, and nerve on muscle fibre synapses. At least 13 motor axons were found to supply each small muscle or cluster of muscle fibres in a large muscle. Each muscle arm simultaneously makes synaptic contact with 3 to 7 axons. Nerve on muscle junctions contain from 1 to 8 axons, each making synaptic contacts. The details of the postsynaptic endplate-specializations resemble those seen in mammalian endplates and are markedly different from both arthropod and annelidan neuromuscular synapses.