Intrinsic properties of the sodium sensor neurons in the rat median preoptic nucleus

Abstract

The essential role of the median preoptic nucleus (MnPO) in the integration of chemosensory information associated with the hydromineral state of the rat relies on the presence of a unique population of sodium (Na+) sensor neurons. Little is known about the intrinsic properties of these neurons; therefore, we used whole cell recordings in acute brain slices to determine the electrical fingerprints of this specific neural population of rat MnPO. The data collected from a large sample of neurons (115) indicated that the Na+ sensor neurons represent a majority of the MnPO neurons in situ (83%). These neurons displayed great diversity in both firing patterns induced by transient depolarizing current steps and rectifying properties activated by hyperpolarizing current steps. This diversity of electrical properties was also present in non-Na+ sensor neurons. Subpopulations of Na+ sensor neurons could be distinguished, however, from the non-Na+ sensor neurons. The firing frequency was higher in Na+ sensor neurons, showing irregular spike discharges, and the amplitude of the time-dependent rectification was weaker in the Na+ sensor neurons than in non-Na+ sensor neurons. The diversity among the electrical properties of the MnPO neurons contrasts with the relative function homogeneity (Na+ sensing). However, this diversity might be correlated with a variety of direct synaptic connections linking the MnPO to different brain areas involved in various aspects of the restoration and conservation of the body fluid homeostasis.

Multiple episodes of sodium depletion in the rat: a remodeling of the electrical properties of median preoptic nucleus neurons

“…Indeed, our laboratory previously showed that the local application of a hyperosmotic/isonatriuric stimulus (350 mOsm/kg H 2 O with mannitol; 150 m m NaCl) had no apparent effect on the excitability of the ventral MnPO neurons (Grob et al ., ; Tremblay et al ., ). The typical hypernatriuric aCSF‐induced depolarisation was considered to be the electrophysiological fingerprint of Na + sensor neurons (Voisin et al ., ).…”

“…The population of MnPO Na + sensor neurons was also characterised by the presence of distinct membrane rectifications in response to hyperpolarising current steps (Fig. A) (Voisin et al ., ). Our results revealed the distribution of these rectifying properties in Na + sensor neurons of the 1D and 3D groups (Fig.…”

“…Specifically, the MnPO is known to play a major role in the detection of extracellular Na + concentration and osmolality variations. Electrophysiological studies demonstrated that a large population of the MnPO was identified according to its responsiveness to extracellular Na + level (Grob et al ., ; Tremblay et al ., ; Voisin et al ., ). These neurons were able to transduce a change in extracellular [Na + ] into a change in their excitability, thereby adjusting the firing rate in response to environmental Na + level variations (Grob et al ., ; Tremblay et al ., ).…”

Extracellular Na+ levels regulate formation and activity of the NaX/alpha1-Na+/K+-ATPase complex in neuronal cells

“…It has been proposed that extracellular sodium ([Na + ] out ) variations are measured mainly by an atypical sodium channel, namely Na X , a recognized Na + -sensor (Hiyama et al, 2002 , 2004 ; Grob et al, 2004 ; Noda, 2006 ). Moreover, 80% of MnPO neurons express this atypical sodium channel (Voisin et al, 2012 ). Specifically, Na X channel is a Na + leak channel allowing Na + ions to pass through the membrane, and detect local variations in [Na + ] out (Tremblay et al, 2011 ).…”