<P> Recent research indicates that glial cells of the hippocampus and cerebellum participate in synaptic transmission, regulate the clearance of neurotransmitters from the synaptic cleft, and release gliotransmitters such as ATP, which modulate synaptic function . </P> <P> Astrocytes are crucial in clearance of neurotransmitters from within the synaptic cleft, which provides distinction between arrival of action potentials and prevents toxic build - up of certain neurotransmitters such as glutamate (excitotoxicity). It is also thought that glia play a role in many neurological diseases, including Alzheimer's disease . Furthermore, at least in vitro, astrocytes can release gliotransmitter glutamate in response to certain stimulation . Another unique type of glial cell, the oligodendrocyte precursor cells or OPCs, have very well - defined and functional synapses from at least two major groups of neurons . The only notable differences between neurons and glial cells are neurons' possession of axons and dendrites, and capacity to generate action potentials . </P> <P> While glial cells in the PNS frequently assist in regeneration of lost neural functioning, loss of neurons in the CNS does not result in a similar reaction from neuroglia . In the CNS, regrowth will only happen if the trauma was mild, and not severe . When severe trauma presents itself, the survival of the remaining neurons becomes the optimal solution . However, some studies investigating the role of glial cells in Alzheimer's Disease are beginning to contradict the usefulness of this feature, and even claim it can "exacerbate" the disease . In addition to impacting the potential repair of neurons in Alzheimer's Disease, scarring and inflammation from glial cells have been further implicated in the degeneration of neurons caused by Amyotrophic lateral sclerosis . </P> <P> In addition to neurodegenerative diseases, a wide range of harmful exposure, such as hypoxia, or physical trauma, can lead to the end result of physical damage to the CNS . Generally, when damage occurs to the CNS, glial cells cause Apoptosis among the surrounding cellular bodies . Then, there is a large amount of microglial activity, which results in inflammation, and finally, there is a heavy release of growth inhibiting molecules . </P>

Which of these cells are not a type of neuroglia found in the cns