Anatomical remodelling of the supraoptic nucleus: changes in synaptic and extrasynaptic transmission.

The adult hypothalamic-neurohypophysial system undergoes activity-dependent
morphological plasticity that modifies the astrocytic enwrapping of its
magnocellular neurones. For a long time, the functional consequences of such
changes have remained hypothetical. Modifications in the glial environment of
neurones are expected to have important physiological repercussions in view of
the various functions played by astrocytes in the central nervous system. In
particular, glial cells are essential for uptake of neurotransmitters, including
glutamate, and for physically and functionally restricting diffusion of
neuroactive substances within the extracellular space. Recent studies performed
in the supraoptic nucleus of lactating and chronically dehydrated animals, in
conditions where astrocytic coverage of neurones is reduced, have revealed a
significant impairment of glutamate clearance. The resulting accumulation of the
excitatory amino acid in the extracellular space around glutamatergic inputs
causes an enhanced activation of presynaptic metabotropic glutamate receptors
that inhibit transmitter release. In the supraoptic nucleus of lactating rats,
neuroglial remodelling is accompanied by modification of the geometry, size and
diffusion properties of the extracellular space. The latter observations suggest
that, in the activated supraoptic nucleus, the range of action and the
concentration of released neuroactive substances may be significantly enhanced.
Overall, our observations indicate that the glial environment of supraoptic
neurones influences synaptic glutamatergic transmission, as well as extrasynaptic
forms of communication.

 

Auteurs Bordeaux Neurocampus