Statocyst, Input, Multimodal Interactions, and Their Effects on Motor Outputs in the Norway Lobster, Nephrops norvegicus (L.)

Knox, Paul Charles (1986) Statocyst, Input, Multimodal Interactions, and Their Effects on Motor Outputs in the Norway Lobster, Nephrops norvegicus (L.). PhD thesis, University of Glasgow.

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The statocyst organ in Decapod crustaceans detects body tilt. It is a powerful input to various equilibrium pathways. A range of techniques have been used to study the transmission of statocyst information and the effects of this information on thoracic and abdominal motor systems in Nephrops novegicus . Interneurons carrying information from the statocysts were recorded in the circumoesophageal connectives. Three different types of interneuron were recorded; of these, one responded best to tilt in the roll plane, while the other two responded best to tilt in the pitch plane but with apposite polarities. Combinations of pitch and roll, produced responses in these interneurons which, while maintaining the same phase position, decreased in size as the preparation was moved out of the preferred plane of tilt. These interneurons showed little or no response to various types of leg stimulation. The responses of intact animals to body tilt were investigated by tilting animals in a large seawater tank; responses were recorded on videotape. Tilt in the roll plane produced a range of responses, the most prominent of which was an asymmetric leg response. Legs on the lowered side cycled in a patterned manner while legs on the raised side were held in a protracted and levated position. This response is distinct from previously reported patterns of leg activity such as walking and "waving". After leg autotomy, this pattern of leg activity was abolished. Coordination was found between the cycling of the legs and the beating of the swimmerets during tilt in the roll plane. This was compared with the coordination between legs and swimmerets during walking. Tilts in the pitch plane resulted in systematic alterations of abdominal posture. Head-down tilt produced a marked abdominal flexion and head-up tilt produced extension. An examination of the responses of swimmerets to tilt in this plane showed that the angle of the powerstroke during head-down tilt was intermediate between the laterally directed powerstroke seen during tilt in the roll plane, and the rearward beat seen during head-up tilt. Recordings made in the swimmeret system revealed at least one tonically active returnstroke motoneuron which received input from the statocysts. Pitching the preparation head down caused an increase of firing frequency in this unit. This unit has been anatomically and physiologically identified as one of the returnstroke motoneurons. Recordings made from the slow abdominal flexor motoneurons revealed a sensitivity to tilt in the pitch plane. However, they responded in an opposite manner to the tonic returnstroke unit. The peripheral inhibitor to this muscle was also recorded. It fired in phase with the tonic returnstroke unit. Interactions between statocysts, legs and swimmerets were investigated at the behavioural level. Substrate contact prevented expression of asymmetric swimmeret responses to roll. However it was possible to demonstrate that this effect is not due to physical contact between the substrate and the terminal segment of the leg, the dactylopodite. In the absence of substrate contact, swimmeret beating was nevertheless inhibited when leg cycling was prevented by blocking leg movement at the proximal joints. Blocking leg movement on one side of the body was sufficient to suppress the swimmeret responses on both sides. In conclusion, information from the statocysts is carried by unimodal interneurons. This information is available to both the swimmerets and the abdominal pasture system. In the absence of swimmeret beating, statocyst information continues to reach the swimmeret system where it determines the output of a tonic returnstroke motoneuron. Substrate contact radically alters the effect of statocyst input. This finding poses specific questions as to the precise nature of the interaction between descending statocyst information, leg input and output patterns, and the swimmeret and abdominal posture motor systems. This may be an ideal system for investigating interactions between the pattern generators of two different systems, specifically the legs and swimmerets, and the role of different types of sensory input in these systems.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Zoology
Date of Award: 1986
Depositing User: Enlighten Team
Unique ID: glathesis:1986-77477
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 09:07
Last Modified: 14 Jan 2020 09:07

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