The structure, distribution, and quantitative relationships of the glia in the abdominal ganglia of the horse leech, Haemopis sanguisuga

Abstract

The glial cells in abdominal ganglia of the horse leech Haemopis sanguisuga were studied by electron microscopy and analysed quantitatively to evaluate the suitability of this easily obtainable carnivorous species for physiological studies. Each abdominal ganglion contains eight giant glial cells, 12,000-14,000 small glial cells, and approximately 300 neurons. The giant glial cells constituted 44.6% and the small glial cells 6.4% of the ganglion's volume. The giant glial cells contain glycogen and bundles of filaments that are chiefly located in their periphery, close to the neurons into which they send processes. The small glial cells are frequently surrounded by the giant glial cells but also occur around neuronal perikarya and axon tracts, as well as against the basal lamina and connective tissue layers. The small glial cells contain lysosomes and sometimes form a trophospongium with the neurons. A system of extracellular channels, which is continuous with the basal lamina, indents the giant glial cells and extends around parts of the neurons. The extracellular channels contain a matrix that appears very similar to the basal lamina and to the cytoplasm in the processes of the small glial cells. Some of the extracellular channels contain collagen fibrils. Hemidesmosomes join the matrix-filled extracellular channels to both the neurons and the giant glial cells. Ionic lanthanum has a free access to the neurons and glial cells via the extracellular spaces and matrix-filled channels. Areas of synaptic intermingling rarely contain glial cell processes.

Neuroglial ATP release through innexin channels controls microglial cell movement to a nerve injury

“…Just as for glia in other invertebrates (Oland et al, 2008) and glia and Schwann cells in vertebrates (Son et al, 1996;Griffin and Thompson, 2008), glia are important for nervous system development (Stent and Weisblat, 1985;Weisblat, 2007) and possibly regeneration (Babington et al, 2005) in the leech . The connectives contain thousands of microglia (Kai-Kai and Pentreath, 1981;Morgese et al, 1983). We hypothesized that the innexin family of proteins in glial cells is involved both in the release of ATP after an injury and in the subsequent activation of microglia in the medicinal leech.…”

Individual microglia move rapidly and directly to nerve lesions in the leech central nervous system.

“…Leech microglia, like leech neurons and large glia, resemble their mammalian counterparts in their morphology, physiology, and histochemistry (7)(8)(9). Moreover, resting and reactive microglia in the rat brain are selectively stained on their surfaces by a lectin from Griffonia simplicifolia seeds (10) that also in the leech stains microglia but not large glia and neurons (S. Hockfield, R. McKay, and K.J.M., unpublished data).…”