A Countershading Reflex in Cephalopods Ferguson, Graham P.; Messenger, John B.
Proceedings of the Royal Society. B, Biological sciences,
01/1991, Letnik:
243, Številka:
1306
Journal Article
Recenzirano
Most cephalopods have more chromatophores on the dorsal body surface than on the ventral and these tend to be kept tonically expanded. As a result the dorsal surface is usually darker than the ...ventral, an effect shown by many animals and known as countershading. We report here that when Sepia officinalis, Loligo vulgaris and Octopus vulgaris are rotated 180° around the longitudinal body axis the ventral chromatophores expand, causing darkening, while the dorsal chromatophores retract, causing paling. When animals are rotated through only 90° the chromatophores on the uppermost half of the ventral and dorsal surfaces expand, while those on the lower half retract. This response, which we term the countershading reflex, can be abolished by ablating the statocysts; and experiments in which the direction of incident light is reversed show that the reflex is not driven by sensory input from the eyes. The function of the reflex is presumably to maintain countershading while the animal is momentarily disoriented; this idea is supported by the fact that it lasts only a few seconds.
For the first time, the 14Cdeoxyglucose radioautographic technique has been successfully used to map physiological activity in cephalopod brains. In unilaterally blinded octopus and cuttlefish, the ...optic lobe of the deprived side showed a decreased uptake of the labelled tracer. This suggests that the uptake is related to functional activity. The potential of the 14Cdeoxyglucose technique as a powerful tool in studying the functional organization of cephalopod brains is discussed.
Experiments are described showing unequivocally that transmission at the squid giant synapse can be reversibly blocked by L-glutamate and its agonists kainate, quisqualate and AMPA, though not by ...NMDA. This effect is presumably brought about by desensitization. The glutamate antagonists cis-2,3-PDA, GAMS and the new quinoxalinediones CNQX and DNQX are also potent reversible blockers. These findings provide new evidence that L-glutamate is a transmitter at the giant synapse and further suggest that the glutamate receptor may be of the non-NMDA type.
The chromatophore system of the small loliginid squid Alloteuthis subulata (Mollusca: Cephalopoda) is very simple and the repertoire of body patterns limited. There are red and yellow chromatophores ...only. On the dorsal mantle there are more yellows than reds; on the ventral mantle and there are more reds than yellows. The dorsal reds are larger than the yellows and bear more radial muscles. The significance of these findings is discussed. Alloteuthis subulata Lamarck is a small loliginid, common in shallow water near Plymouth (Holme, 1974; Lipinski, 1985; Rodhouse et al., 1988). Little is known of its natural history and behaviour and chromatophores and body patterns of adults have never been described, although the skin of this species has been used in physiological studies of colour change (Messenger, 1991; Messenger et al., 1991; Cornwell & Messenger, 1995). Over 100 adult animals of both sexes, caught by trawl at depths of 10–60 m, were examined; their mantle lengths ranged from 70 to 130 mm. Living animals were observed in large aquaria with circulating sea-water. Counts and measurements of chromatophores were made on colour photographs (taken through a Nikon dissecting microscope) of pieces of fresh skin (20×20 mm) dissected from animals killed by decapitation or after MgCl2 anaesthesia (Messenger et al., 1985). Chromatophores were counted first when fully retracted (by 1×10−3 M 5-HT) and then when fully expanded (with 1×10−3 M L-glutamate: Cornwell & Messenger, 1995). All measurements were made in the same area of the body: the central and anterior part of the mantle, dorsally and ventrally (Figure 2).
The timing and regional specificity of cerebrospinal fluid (CSF) enlargements have not been well described in schizophrenia. High-resolution magnetic resonance images and computational image analysis ...methods were used to localize cross-sectional changes in lateral ventricle and sulcal and subarachnoid CSF in first episode schizophrenia patients (51 males/21 females) and healthy subjects (37 males/41 females). Volumes were obtained for each lateral ventricle horn and regional differences identified by comparing the distances from the ventricular surfaces to the central core at anatomically matched locations. Extra-cortical CSF differences were compared by measuring the proportion of CSF voxels sampled from spatially homologous cortical surface points. Significant extra-cortical CSF enlargements were observed in first episode patients, where regional differences surrounded the temporal, anterior frontal and parietal cortices. Volume and ventricular surface analyses failed to show significant effects of diagnosis. However, interactions indicated dorsal superior horn expansions in female patients compared with same-sex controls. Since ventricular enlargements are widely reported in chronic patients, our observations at first episode suggest ventricular enlargement may progress after disease onset with early changes occurring around the dorsal superior horn. In contrast, sulcal and subarachnoid CSF increases may be manifest near or before the first episode but after brain development is complete, reflecting pronounced reductions in proximal brain tissue.
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