The structure of the perineuronal sheath of satellite glial cells (SGCs) in sensory ganglia

Abstract

In sensory ganglia each nerve cell body is usually enveloped by a satellite glial cell (SGC) sheath, sharply separated from sheaths encircling adjacent neurons by connective tissue. However, following axon injury SGCs may form bridges connecting previously separate perineuronal sheaths. Each sheath consists of one or several layers of cells that overlap in a more or less complex fashion; sometimes SGCs form a perineuronal myelin sheath. SGCs are flattened mononucleate cells containing the usual cell organelles. Several ion channels, receptors and adhesion molecules have been identified in these cells. SGCs of the same sheath are usually linked by adherent and gap junctions, and are functionally coupled. Following axon injury, both the number of gap junctions and the coupling of SGCs increase markedly. The apposed plasma membranes of adjacent cells are separated by 15-20 nm gaps, which form a potential pathway, usually long and tortuous, between connective tissue and neuronal surface. The boundary between neuron and SGC sheath is usually complicated, mainly by many projections arising from the neuron. The outer surface of the SGC sheath is covered by a basal lamina. The number of SGCs enveloping a nerve cell body is proportional to the cell body volume; the volume of the SGC sheath is proportional to the volume and surface area of the nerve cell body. In old animals, both the number of SGCs and the mean volume of the SGC sheaths are significantly lower than in young adults. Furthermore, extensive portions of the neuronal surface are not covered by SGCs, exposing neurons of aged animals to damage by harmful substances.

P2Y purinergic receptors: New targets for analgesic and antimigraine drugs

“…As already mentioned, SGCs wrap around the cell bodies of primary neurons in sensory ganglia, forming a morphological and functional unit [59]. The key role of SGCs in the development and maintenance of chronic pain has been demonstrated by their increased expression and release of IL-1β [77], TNFα [62], as well as by the increased gap junctionmediated cell coupling [78,79] following nerve injury.…”

“…As detailed below, their contribution to nociception is now firmly acknowledged, both in the periphery and in the CNS (with a primary role played here by microglia and astrocytes) [58] . Within sensory ganglia, the somata of sensory neurons are surrounded and wrapped by a network of satellite glial cells (SGCs), which continually monitor the extracellular milieu and exchange information with one another and with neurons as well, so profoundly affecting neuronal firing and, ultimately, the transmission of painful sensations [59,60]. Thus, targeting glial cells with specific pharmacological compounds has recently emerged as an exciting opportunity for the development of new and effective painkillers.…”

Satellite glial cells: more than just ‘rings around the neuron’

“…In the first article Pannese (2010) describes the ultrastructure of SGCs. That this article will open this issue is appropriate at least for two reasons.…”

Targeting sympathetic glia for treating cardiovascular diseases

“…SGCs form peri-neuronal sheaths that tightly wrap around neuronal soma and axon-soma contacts in sympathetic ganglia [20] . SGCs effectively isolate individual PGNs [20] and comprise an effective chemical barrier for the whole ganglion [21] , suggesting their potential role of governing PGN activity.…”

“…SGCs form peri-neuronal sheaths that tightly wrap around neuronal soma and axon-soma contacts in sympathetic ganglia [20] . SGCs effectively isolate individual PGNs [20] and comprise an effective chemical barrier for the whole ganglion [21] , suggesting their potential role of governing PGN activity. Sympathetic SGCs also express machinery including inward rectifying potassium channels (Kir) [22][23][24] , Ca 2+ -activated potassium channels [24] , gap junctions [24,25] , neurotransmitter transporters [26][27][28][29] , enzymes for neurotransmitter degradation and synthesis [30] , and metabotropic neurotransmitter receptors [31,32] , further suggesting their important roles in modulating ganglionic neuronal activity and signaling processing.…”