Reversal of a hallmark of brain ageing: lipofuscin accumulation.

The prospect of removing cellular deposits of lipofuscin is of considerable interest because they may contribute to age related functional decline and disease. Here, we use a decapod crustacean model to circumvent a number of problems inherent in previous studies on lipofuscin loss. We employ (a) validated lipofuscin quantification methods, (b) an in vivo context, (c) essentially natural environmental conditions and (d) a situation without accelerated production of residual material or (e) application of pharmacological compounds. We use a novel CNS biopsy technique that produces both an anti-ageing effect and also permits longitudinal sampling of individuals, thus (f) avoiding conventional purely cross-sectional population data that may suffer from selective mortality biases. We quantitatively demonstrate that lipofuscin, accrued through normal ageing, can be lost from neural tissue. The mechanism of loss probably involves exocytosis and possibly blood transport. If non-disruptive ways to accelerate lipofuscin removal can be found, our results suggest that therapeutic reversal of this most universal manifestation of cellular ageing may be possible.

Relationship of dorsoventral eyeshine distributions to habitat depth and animal size in mesopelagic decapods.

Eyeshine distribution patterns recorded from the eyes of 19 mesopelagic decapod species were examined and related to the depths at which the species are found. For most species examined, eyeshine was found to be brighter ventrally than dorsally. Deep-water decapod species that do not undergo diel vertical migrations had brighter dorsal eyeshine than migratory species. Eyeshine intensity increased with body size in five of the species examined and decreased in two. These changes in eyeshine intensity may be an adaptation to variations in depth distributions that occur with increasing body size. It is suggested that the depth and size-related changes reflect the importance of remaining camouflaged in the mesopelagic realm and are an example of ecologically functional development.

Cuticular Photophores of Two Decapod Crustaceans, Oplophorus spinosus and Systellaspis debilis.

The organization, ultrastructure, growth, and development of two types of cuticular photophore in oplophorid shrimps (Oplophorus spinosus and Systellaspis debilis) are described. Photophores located in the third maxilliped consist of a unit structure comprising a single photocyte and associated pigment cells. Reflecting pigment cells contain white pigment and form an apical cap above the photocyte; sheath cells contain red carotenoid pigment and form a light-absorbing layer around the photophore. Photophores located on the pleopods are compound structures comprising many photocytes. They also contain the same types of pigment cell that are found in the unit photophores of the maxilliped. Paracrystalline bodies at the apical ends of the photocytes in both types of photophore are thought to be associated with light generation. Both types of photophore have mechanisms for tilting in the pitch plane. In the maxilliped, the apices of the photophores are connected to a ligament that has its origin in the propodus. Flexion or extension of the dactylus displaces the ligament, which tilts the photophores synchronously. The cuticular window beneath each photophore remains stationary. The tilt mechanism of the pleopod photophores is quite different, and depends upon muscular contraction. A main and an accessory longitudinal muscle cause backwards rotation of the photophore by deforming the cuticle surface. A loop muscle that passes around the anterior face of the photophore causes forward rotation. The two mechanisms optimize the use of the photophores in ventral camouflage. They allow photophore rotation to compensate for changes in the shrimp's orientation in the plane of pitch and thus maintain the ventral direction of the luminescence.

Comparative Morphology of the Eyes of Postlarval Bresiliid Shrimps From the Region of Hydrothermal Vents.

The structure and ultrastructure of the eyes of postlarval vent shrimps provisionally designated `Alvinocaris' and `Chorocaris' are described. The eyes of the postlarval `Alvinocaris' are cylindrical, borne on short stalks, and contain closely packed rhabdoms. The ommatidia lack dioptric apparatus and have rhabdoms extending almost to the cornea. The rhabdoms consist of orthogonal layers of microvilli typical of crustacean rhabdoms. The eyes of the `Chorocaris' are similar, but the rhabdom layer extends back through the reduced eyestalks and covers some of the dorsal surface of the cephalothorax. The rhabdoms from both the anterior and the thoracic regions consist of layered microvilli. The eyes of a slightly smaller postlarval vent shrimp, termed `Type A', differ. Although clearly related to the other vent shrimps, Type A has stalked eyes held at an angle to the head. The eye displays a gradient of ommatidial development, with the older ommatidia closely resembling those seen in the other postlarval types. Between the cornea and the rhabdom layer, the youngest ommatidia possess quadripartite crystalline cones similar to those seen in related families of caridean shrimps; these are absent in the more mature ommatidia. The external structure of the anterior and thoracic eyes of juvenile Rimicaris exoculata (after settlement at the vent site) is also described. Juveniles up to 9 mm in carapace length have anterior corneas similar to those seen in postlarvae, whereas in larger specimens the corneas are progressively replaced by an ocular plate.

Generating precise mechanical stimuli and recording chordotonal organ discharge patterns using a microcomputer.

A computer-controlled system for the investigation of the response properties of the tibio-femoral chordotonal organ in the locust is described. The computer is used to generate small amplitude sinusoidal movements of the tibia via a small servo-controlled motor. The resulting response recorded via a suction electrode is simultaneously detected, processed and stored on disk. Full constructional details for all hardware required are given. The software, developed for a BBC microcomputer, in addition to controlling all the hardware, has graphics and analysis routines enabling the operator to display and manipulate the stored data.

Regeneration of the eye margin in Periplaneta americana (Insecta, Blattodea).

The regulative ability of the proliferative zone of the insect eye margin has been investigated in larval Periplaneta americana. After sections of the eye margin are removed the eye nevertheless recovers to form a normal shape. Using chimaeras of lavender and wild-type animals we were able to show that the margin can regenerate from the differentiated parts of the eye. When differentiated eye tissue is confronted with epidermis from the head capsule adjacent to the proliferative zone (the vertex), the regenerated margin always forms from the eye. There is no evidence that intervening levels can be intercalated between host and graft tissues when sections of the eye margin are moved to new circumferential levels. However, in that situation differences between tissues from non-adjacent circumferential positions lead to the rounding up of the graft and it fails to develop normally.

Naturally occurring abnormalities (Bruchdreifachbildungen) in the chelae of three species of Crustacea (Decapoda) and a possible explanation.

Naturally occurring abnormalities (Bruchdreifachbildungen) in decapod crustacean appendages are described. They are similar to the range of structures experimentally produced by cutting notches in the sides of insect legs (Bohn, 1965). It is argued that they result from failure of wounds to heal. Regeneration from a free surface along the proximodistal axis is always in a distal direction. Surfaces regenerating circumferentially can regenerate in either direction around the circumference. Regeneration will proceed until the two surfaces of the wound meet. Then, where the two surfaces on either side are non-congruent, intervening tissues will be intercalated. This explanation accounts for the range of structures observed after notching experiments (Bohn, 1965) and seen in crustacean Bruchdreifachbildungen. The explanation says that regeneration will occur wherever wounds fail to heal. This avoids the difficulties of the complete circle rule (French, Bryant & Bryant, 1976) and explains why appendages with mirror-image symmetry are often capable of regeneration.

A Golgi-electron-microscopical study of the structure and development of the lamina ganglionaris of the locust optic lobe.

The gross structure as well as the neuronal and non-neuronal components of the lamina ganglionaris of the locust Schistocerca gregaria are described on the basis of light- and electron-microscopical preparations of Golgi (selective silver) and ordinary histological preparations. The array of optic cartridges within the lamina neutropile--their order and arrangement--and the composition of the cartridges are described. There are six types of monopolar neurons: three whose branches reach to other cartridges and three whose branches are confined to their own cartridges. Retinula axons terminate either in the lamina or the medulla neuropiles. There are three types of centrifugal neurons, two types of horizontal neuron, as well as glia and trachea in the lamina neuropile. The development of the lamina neuropile is described in terms of developing monopolar and centrifugal axons, growing retinula fibres, and composition of the developing optic cartridges.

The eye margin and compound-eye development in the cockroach: evidence against recruitment.

The compound eye of the cockroach nymph grows from stadium to stadium by the addition of new ommatidia to the growing edge of the eye. By a series of transplant operations on Periplaneta americana and from SEM studies on Gromphadorhina portentosa it is shown that the proliferating region of the eye margin is a budding zone. There is no recruitment of larval head-capsule epidermis into the eye.

Post-embryonic determination of the ecdysial line in the cockroach: evidence for pattern regulation in the medio-lateral axis.

By removing or transplanting sections of the ecdysial line in the cockroach Gromphadorhina portentosa, pattern regulation in medio-lateral axis of an insect has been demonstrated. The line can reform after sections have been removed and when epidermal grafts from either side of the midline are grafted with confronting medial edges. The results are explicable in terms of known mechanisms for pattern regulation in insects.

Cell lineage and cell determination in the developing compound eye of the cockroach, Periplaneta americana.

By grafting between eye colour mutants of the cockroach Periplaneta americana we have investigated (i) the hypothesis that cells within an ommatidium of the fused rhabdom type are clonally derived from a single mother cell and (ii) we have tested the suggestion that cells from non-prospective eye epidermis can form ommatidia when grafted next to eye tissue. Mosaic eyes containing cells of the two genotypes contain ommatidia with unpredictable combinations of the two sorts of cells at the host/graft border. This finding is inconsistent with the first hypothesis. Using grafts of prothoracic epidermis and head epidermis from non-prospective eye regions we have shown that only cells from the prospective eye region can form ommatidia. Possible ways that eye cells could be determined are discussed in the light of these findings.

Cell junctions in the developing compound eye of the desert locust Schistocerca gregaria.

Intercellular junctions in the developing retina of the locust Schistocerca gregaria have been examined by electron microscopy. Different types of junction appear in a well defined sequence during development. Five stages of ommatidial development are described. Close junctions and punctate junctions are present throughout development. Gap junctions appear transiently amongst the undifferentiated cells, before clearly defined preommatidia can be distinguished. The subsequent disappearance of gap junctions may be correlated with cell determination. Lanthanum studies confirm these findings. The later sequential appearance of adhesive junction types is described. These include septate desmosomes and two types of desmosomes. In the fully differentiated ommatidium only two types of junction remain, these are: desmosomes and rhabdomeric junctions.

The determination of polarity in the developing insect retina.

The retina in Oncopeltus fasciatus is a polarized structure in which all ommatidia are orientated the same way. By a series of grafting experiments we have shown that the orientation of ommatidia is partly dependent upon the orientation of the epidermis from which they develop and partly on the orientation of the host eye. Grafts which invert the forsoventral axis of the presumptive eye epidermis do not disrupt the orientation of the nascent ommatidia. Grafts which are rotated by 90 degrees or 180 degrees produce altered patterns of orientation. The polarity of the epidermis is to some extent conserved in these cases. Significantly ommatidia at the graft/host border take up orientations intermediate between the extremes found in the graft and host. Small rotated grafts assume the polarity of the host retina. These results are compared with the effects of similar grafts on developing insect bristle patterns.