A blood-derived attachment factor enhances the in vitro growth of two glial cell types from adult cockroach.

Reactive glial cells from chemically-lesioned areas of the central nervous system (CNS) of adult cockroaches (Periplaneta americana) have been grown in vitro on a substrate of fibronectin. This paper reports the enhancement of growth that is achieved when blood cells, serum, or medium conditioned by a 2-h incubation with blood cells are used as an alternative substrate. Glial cells rapidly grew out from connective explants to form extensive radial mats of cells linking up with those from adjacent explants on each of the blood-derived substrates. In addition to supporting the growth of reactive glial cells, characterised by their long, thin, branching morphology, these substrates also revealed the presence of a second type of glial cell, not previously found on fibronectin. Such cells, derived from ganglionic explants, behaved in a very different way to the reactive glia, initially spreading out to form a flattened sheet of phase-bright cells, before migrating away over the culture surface. The growth-enhancing effects of this blood-derived factor may play a role in the events following damage to the insect CNS, where it is known that the entry of blood cells into the lesion site is an important precursor to the rapid and structured repair seen in this system.

The long visual fibers of the dragonfly optic lobe: their cells of origin and lamina connections.

A pair of long visual fibers projects from each ommatidium of the compound eye of the dragonfly Sympetrum. They arise from retinular cell R7 and its slender partner R6. To investigate the segregation of lamina input pathways between these and the well-described short retinular terminals, we have examined the cell morphology and en passant synaptic involvements of R7 and 6 in the ventral lamina using serial-EM and combined Golgi-EM. In the retinula, R7 has a large apical rhabdomere with microvilli aligned along the animal's horizon, and a basal axon. R6 has a few microvilli at all depths, which align with those of neighboring rhabdomeres. In the lamina, R7 and 6 neighbor on MV, the fifth monopolar cell. The stout axon of R7 has many diffusely distributed spines which contact the neighboring terminals of R5 and 8, and MII. In one entire cartridge R7 was presynaptic to MII at 24 dyads and triads throughout the lamina and also to MV at dyads exclusively in the distal lamina. Another class of element which derives from the unidentified processes called alpha was also postsynaptic to R7 at dyads, and, mostly in the proximal lamina, was reciprocally presynaptic to R7, along with R5 and 8. R6 is slender with a single conspicuous spine. At a total of three zones in the proximal lamina and distal chiasma it was presynaptic at 38 dyads--also upon MII and MV and often in combination with other elements; it was not postsynaptic in the lamina. R6 and 7 thus provide the sole input to MV and contribute to the general retinular input to MII. They form the lowest ratios of triad:dyad synapses of all lamina retinular elements. Comparison is made with the long visual fibers of other arthropods but known examples are too diverse to detect functional commonalities.

The number and arrangement of elements in the lamina cartridge of the dragonfly Sympetrum rubicundulum.

Five monopolar cells and two long visual fibres are a consistent component of the lamina cartridge of the ventral half of the eye of the dragonfly Sympetrum rubicundulum. They communicate with the chiasm via a cartridge axon bundle comprising a minimum of ten fibres. The arrangement of these elements is documented with respect to the ommatidial photoreceptor axon bundle innervating them. These relationship are described both within the lamina cortex and in the cross-section of the underlying cartridge.