Proceedings of The Physiological Society
University College Dublin (2009) Proc Physiol Soc 15, PC207
In vivo behaviours of squid motor units during denervation of neighbouring units.
1. stazione Zoologica Naples, La Garde-Freinet, France.
Figure 1. Detail of the mantle of a squid showing myogenic enhancement of motor unit end-organ activity resulting from DSS in the hours (18-40h) following section of the nerve supply to surrounding skin. (Mature squid seen from left side, dorso-lateral view: LPN incompletely sectioned, right side of mantle (above) intact; dashed line = dorsal midline; yellow circle = ROI; below, selected spots in black: numbers = expanded size ratios relative to resting size (d); arrows indicate identical spots in a) to d). Temperature 20-22°C)
Figure 2 Single 'residual unit' (see text) a) 5days, b) 16days post-operation
The chromatophore system of the squid Loligo vulgaris, run by central motor neurones, generates images that can be recorded photographically (in the laboratory) at intervals while animals are being maintained in their holding tanks. The poster reports on image-analysis of two phenomena (supersensitivity, sprouting) visible in the output history of ‘residual’ chromatophore motor units in a partially denervated environment during the days following incomplete section of the pallial nerve on one side of the body [1,2]. Supersensitivity. The output amplitude of single units of multiply innervated dark chromatophores (spots)  is affected by their denervated neighbours through the intra-chromatophore coupling of a spot’s several muscle fibres (~25 on any one spot). The progress of this myogenic enhancement during the hours following section of the left pallial nerve (LPN) under light anaesthesia (<1% ethyl alcohol in seawater) is seen in Figure 1. Whenever the animal changes colour, the ‘residual’ unit on the left side of the mantle (yellow ring) behaves synchronously with similar ones on the right side (upper in the figure); expanded amplitude of individual spots is low at 18h post-operation (a), while neuromuscular endings of neighbouring units are still intact, and increases as muscle denervation supersensitivity (DSS) develops to a maximum at 40h (b, c). Interestingly, when the squid turns pale (d), DSS is suppressed through unknown mechanisms. Sprouting. Figure 2 shows a second residual unit that had been spared by LPN section, a) at 5 days post-operation, b) at 16 days. Over the intervening 11 days, the motor field of this unit nearly doubled in area through the capture of neighbouring (denervated) spots of several size classes. Further enlargement of this unit did not occur in the remaining weeks before sacrifice.
Where applicable, experiments conform with Society ethical requirements