Morphological plasticity of the rat supraoptic nucleus – cellular consequences

Abstract

The supraoptic nuclei of the hypothalamus display a remarkable anatomical plasticity during lactation, parturition and chronic dehydration, conditions associated with massive neurohypophysial hormone secretion. This structural remodeling is characterized by a pronounced reduction of the astrocytic coverage of oxytocin neurons, resulting in an increase in the number and extent of directly juxtaposed neuronal surfaces. Although the exact role played by such an anatomical remodeling in the physiology of the hypothalamo-neurohypophysial system is still unknown, several findings obtained over the last decade indicate that synaptic and extrasynaptic transmissions are impacted by these structural changes. We review these data and try to extrapolate how such changes at the cellular level might affect the overall activity of the system. One repercussion of the retraction of glial processes is the accumulation of glutamate in the extracellular space. This build-up of glutamate causes an increased activation of pre-synaptic metabotropic glutamate receptors, which are negatively coupled to neurotransmitter release, and a switch in the mode of action of pre-synaptic kainate receptors that control GABA release. Finally, the range of action of substances released from astrocytes and acting on adjacent magnocellular neurons is also affected during the anatomical remodeling. It thus appears that the structural plasticity of the hypothalamic magnocellular nuclei strongly affects neuron-glial interactions and, as a consequence, induces significant changes in synaptic and extrasynaptic transmission.

Astroglial cradle in the life of the synapse

“…The perisynaptic astroglial sheaths covering synapses are exceedingly thin, the profiles of these perisynaptic structures being on average less than 200 nm (and often less than 100 nm) in diameter [22]. Importantly, astroglial PAPs demonstrate remarkable morphological plasticity, when through retracting or extending astroglial membranes the degree of synaptic coverage can be dynamically regulated [25]. It has to be noted, however, that the data on synaptic coverage by astroglial processes remain generally insufficient with only a few brain regions being investigated; the detailed cartography of astroglial synaptic profiles throughout the CNS is very much longed for.…”

Effect of Manganese Chloride on the Neurochemical Profile of the Rat Hypothalamus

“…Due to dehydration, morphological plasticity of astrocytes in the PVN occurred. Thus, synaptic and extrasynaptic transmission in magnocellular neurons of the PVN were modified with increased synaptic release of glutamate and GABA but reduced ability of Tau to bind to glycinergic receptors and modulate neuronal excitability (Oliet and Bonfardin, 2010).…”

Astroglial potassium clearance contributes to short‐term plasticity of synaptically evoked currents at the tripartite synapse

“…Astrocytes, like neurons, exhibit several forms of plasticity, including a morphological plasticity of neuronal coverage during specific physiological conditions (Genoud et al 2006;Oliet & Bonfardin, 2010), as well as a functional plasticity of neuronal-induced currents. In the cerebellum, currents evoked in Bergmann glia by parallel fibre stimulation exhibit activity-dependent short-term and long-term plasticity (Bellamy & Ogden, 2005, while in the hippocampus, astroglial potassium signals display LTP, like neuronal currents (Ge & Duan, 2007;Zhang et al 2009).…”