Lactate is an energy substrate for rodent cortical neurons and enhances their firing activity

Glucose is the mandatory fuel for the brain, yet the relative contribution of glucose and lactate for neuronal energy metabolism is unclear. We found that increased lactate, but not glucose concentration, enhances the spiking activity of neurons of the cerebral cortex. Enhanced spiking was dependent on ATP-sensitive potassium (KATP) channels formed with KCNJ11 and ABCC8 subunits, which we show are functionally expressed in most neocortical neuronal types. We also demonstrate the ability of cortical neurons to take-up and metabolize lactate. We further reveal that ATP is produced by cortical neurons largely via oxidative phosphorylation and only modestly by glycolysis. Our data demonstrate that in active neurons, lactate is preferred to glucose as an energy substrate, and that lactate metabolism shapes neuronal activity in the neocortex through KATP channels. Our results highlight the importance of metabolic crosstalk between neurons and astrocytes for brain function.

Neural connectivity between the hypothalamic supramammillary nucleus and appetite- and motivation-related regions of the rat brain

The supramammillary nucleus (SuM) has an emerging role in appetite control. We have shown that the rat SuM is activated during hunger or food anticipation, or by ghrelin administration. In the present study, we characterised the connectivity between the SuM and key appetite- and motivation-related nuclei in the rat. In adult wild-type rats, or rats expressing Cre recombinase under the control of the tyrosine hydroxylase (TH) promoter (TH-Cre rats), we used c-Fos immunohistochemistry to visualise and correlate the activation of medial SuM (SuMM) with activation in the lateral hypothalamic area (LH), the dorsomedial hypothalamus (DMH) or the ventral tegmental area (VTA) after voluntary consumption of a high-sugar, high-fat food. To determine neuroanatomical connectivity, we used retrograde and anterograde tracing methods to specifically investigate the neuronal inputs and outputs of the SuMM. After consumption of the food there were positive correlations between c-Fos expression in the SuMM and the LH, DMH and VTA (P = 0.0001, 0.01 and 0.004). Using Fluoro-Ruby as a retrograde tracer, we demonstrate the existence of inputs from the LH, DMH, VTA and ventromedial hypothalamus (VMH) to the SuMM. The SuMM showed reciprocal inputs to the LH and DMH, and we identified a TH-positive output from SuMM to DMH. We co-labelled retrogradely-labelled sections for TH in the VMH, or for TH, orexin and melanin-concentrating hormone in the LH and DMH. However, we did not observe any colocalisation of immunoreactivity with any retrogradely-labelled cells. Viral mapping in TH-Cre rats confirms the existence of a reciprocal SuMM-DMH connection and shows that TH-positive cells project from the SuMM and VTA to the lateral septal area and cingulate cortex, respectively. These data provide evidence for the connectivity of the SuMM to brain regions involved in appetite control, and form the foundation for functional and behavioural studies aiming to further characterise the brain circuitry controlling eating behaviours.

Amygdala Kisspeptin Neurons: Putative Mediators of Olfactory Control of the Gonadotropic Axis

Kisspeptins and their receptors are potent regulators of the gonadotropic axis. Kisspeptin neurons are found mainly in the hypothalamic arcuate nucleus and the anteroventral periventricular nucleus. However, there is also a third population of kisspeptin neurons, located in the amygdala. We used fluorescence immunohistochemistry to quantify and localize the amygdala kisspeptin neurons and to reveal close apposition and putative innervations by vasopressinergic and tyrosine hydroxylase-positive dopaminergic neurons. Using microinjections of retro- and anterograde tracers, and viral transfection systems in rats and transgenic mice, we showed reciprocal connectivity between the accessory olfactory bulb and the amygdala kisspeptin neurons. In vitro recordings indicate an inhibitory action of kisspeptin on mitral cells in the accessory olfactory bulb. Using viral specific-cell gene expression in transgenic mice in combination with double immunofluorescence histochemistry, we found that the amygdala kisspeptin neurons also project to gonadotropin-releasing hormone (GnRH) neurons in the preoptic area. Our neuroanatomical and electrophysiological data suggest that amygdala kisspeptin neurons integrate social behaviour and odour information into GnRH neurons in the preoptic area to coordinate the gonadotropic axis and the appropriate output behaviour to odour cues.

Design and validation of a homogeneous time-resolved fluorescence cell-based assay targeting the ligand-gated ion channel 5-HT3A

Ligand-gated ion channels (LGICs) are considered as attractive protein targets in the search for new therapeutic agents. Nowadays, this strategy involves the capability to screen large chemical libraries. We present a new Tag-lite ligand binding assay targeting LGICs on living cells. This technology combines the use of suicide enzyme tags fused to channels of interest with homogeneous time-resolved fluorescence (HTRF) as the detection readout. Using the 5-HT3 receptor as system model, we showed that the pharmacology of the HALO-5HT3 receptor was identical to that of the native receptor. After validation of the assay by using 5-HT3 agonists and antagonists of reference, a pilot screen enabled us to identify azelastine, a well-known histamine H1 antagonist, as a potent 5-HT3 antagonist. This interesting result was confirmed with electrophysiological experiments. The method described here is easy to implement and could be applicable for other LGICs, opening new ways for the screening of chemical libraries.

Stobadine-induced hastening of sensorimotor recovery after focal ischemia/reperfusion is associated with cerebrovascular protection

In a model of 1 hour-intraluminal occlusion of rat middle cerebral artery (MCA), we investigated the spontaneous recovery of vascular functions and functional deficit together with ischemia volume evolution at 24 h, 3 days and 7 days of reperfusion. Infarct cerebral volumes and edema were quantified with histological methods. Endothelium-dependent and smooth muscle potassium inward rectifier current (Kir2.x)-dependent relaxing responses of MCA were tested using Halpern arteriograph and Kir2.x current density evaluated on MCA myocytes with whole-cell patch-clamp technique. Sensorimotor recovery was estimated according to performances obtained with adhesive removal test and prehensile traction test. A time-dependent improvement of smooth muscle K(+)-dependent vasorelaxation and Kir2.x current density is observed at 7 days of reperfusion while endothelium-dependent relaxation is still impaired. In parallel a significant reduction of functional deficit is observed at 7 days of reperfusion together with a time-matched reduction of striatal infarct and edema volumes. Administration of an antioxidant agent, stobadine, at time of reperfusion and 5 h later allowed: (i) a neuroprotective effect with a significant reduction of infarct size compared to vehicle-treated rats; (ii) a prevention of endothelial-dependent relaxation and Kir2.x current density reductions of MCA ipsilateral to occlusion; (iii) a hastening of the functional recovery. The beneficial effect of stobadine underlines a link between vascular protection, neuronal protection and sensorimotor recovery that could become a promising pharmacological target in the treatment of cerebral ischemia.

Neurogliovascular unit after cerebral ischemia: is the vascular wall a pharmacological target

Ischemic stroke induces drastic alterations of the functions of the neurogliovascular unit with dramatic consequences on the well-being of the patients in terms of cognitive and motor handicap. Nowadays, only very few therapeutics are available as a treatment of ischemic stroke. Ischemia is a multifactorial pathology involving different cerebral cellular components such as neurons, astrocytes and vessels working as a functional unit. Recent experimental strategy investigation involving different agents with antioxidant properties (dt-BC, stobadine) or pleiotropic effects (lipopolysaccharide, LPS) has been developed to evaluate whether the vascular wall could be considered as a potential target in neuroprotection concept.