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Journal of Experimental Biology 155,605-627 (1991)
Published by Company of Biologists 1991

The Coordinated Action of Abdominal Postural and Swimmeret Motor Systems in Relation to Body Tilt in the Pitch Plane in the Norway Lobster Nephrops Norvegicus

PAUL C. KNOX ¹ and DOUGLAS M. NEIL ²

¹ Neurobiology Laboratory, Department of Zoology, University of Glasgow, Glasgow G12 8QQ, Scotland; Department of Pharmacology, University of Edinburgh, 1 George Square, Edinburgh EH8 9JZ
² Neurobiology Laboratory, Department of Zoology, University of Glasgow, Glasgow G12 8QQ, Scotland

To whom reprint requests should be addressed

The responses of the abdominal positioning system and the swimmerets of the Norway lobster Nephrops norvegicus to tilts in pitch and in other vertical planes have been investigated in intact and semi-intact preparations.

Tilt of the intact animal in the pitch plane evoked abdominal flexion with the head up and extension with the head down. The response amplitudes were largely independent of tilt angle, and the null point for switching between flexion and extension responses was at the 10° head-up position, which corresponds to the normal posture of the animal. Intersegmental joint angles in the abdomen were significantly different for head-up and head-down tilts. These pitch responses were dependent upon the integrity of the statocysts.

Tilts in different vertical planes demonstrated that the abdominal flexion/extension response was restricted to a range of tilts within ±5° of true pitch. Outside this range, tilts in both directions elicited abdominal extension, which was accompanied by asymmetrical movements of the uropods and swimmerets.

In semi-intact preparations, recordings from the motor supply to the abdominal superficial flexor muscles demonstrated a modulation of activity in response to tilt in the pitch plane: several small excitatory axons increased their discharge in the head-up position, while the inhibitory axon f5 fired when the head was down. With tilts in different vertical planes this pattern of firing persisted from pitch almost to roll.

The effects of tilt in the pitch and roll planes on the temporal and spatial parameters of swimmeret beating were studied in intact animals. Swimmeret beating was bilaterally symmetrical in pitch: vigorous in the head-down position, when the powerstrokes were directed about 25° to the side, and weak in the headup position, when the powerstrokes were directed to the rear. Responses in roll

Key words: equilibrium, abdominal posture, swimmerets, Norway lobster, Nephrops norvegicus

Accepted on September 18, 1991

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