According to the hypothesis of “lactate shuttle”, glycogen stored in astrocytes can be converted to lactate and exported to neurones as a preferred fuel (1). However, we employed optogenetics to investigate the signalling mechanism between astrocytes and noradrenergic (NAergic) neurones and here present data to suggest that lactate also plays a role in astrocyte-to-neurone communication. To selectively stimulate Gq- and Gs-protein-mediated signalling cascades in astrocytes, we generated adenoviral vectors and expressed the opsin-GPCR chimeras, Optoα1- and Optoβ2-adrenergic receptors (Optoα1AR; Optoβ2AR) (2) under control of a transcriptionally enhanced GFAP promoter (3). We verified that these constructs activated the correct GPCR pathways in astrocytes (presented at the 2011 Physiological society meeting (4)). To confirm that astrocytes break down glycogen to produce lactate, primary dissociated glial cultures expressing Optoα1AR and Optoβ2AR and loaded with the pH indicator Snarf-5 were imaged ratiometrically using a Leica SP1 confocal microscope. Stimulation with 470nm light resulted in a significant change in the fluorescence ratio, indicative of acidification and consistent with the production of L-lactate (Optoα1AR: +132.8% ± 3.4%, n=44 cells, p<0.001; Optoβ2AR: +147.4% ± 3.6%, n=36 cells, p<0.001; paired t-test). This effect could be blocked by pre-incubation with an inhibitor of glycogen breakdown, 1,4-dideoxy-1,4-imino-D-arabinitol (DAB; 500 μM; Optoα1AR: +101.9% ± 0.3%, n=26 cells, p<0.001; Optoβ2AR: +101.3% ± 0.7%, n=34 cells, p<0.001). Fast scan cyclic voltammetry (FCV) in organotypic slices containing the locus coeruleus (LC) was used to measure NA release from NAergic neurones. To determine whether L-lactate released from astrocytes can stimulate NA release, astrocytes were transduced to express Optoα1AR or Optoβ2AR. Stimulation of astrocytes with a 445nm PhoxX diode laser induced release of NA (Optoα1AR: +85.2 ± 12.2 V*Sec, n=24 stimulations, p<0.001; Optoβ2AR: +88.7 ± 11.1 V*Sec, n=20, p<0.001; paired t-test). Pre-incubation with DAB blocked the effect of optogenetic stimulation of astrocytes on NA release (Optoα1AR: -11.16 ± 11.7 V*Sec, n=6, p<0.001; Optoβ2AR: -14.74 ± 7.0 V*Sec, n=5, p<0.001). These experiments suggest that signalling mediated by Gq/sPCRs in astrocytes could potentiate the release of NA from LC neurones via L-lactate. Consistent with this idea, application of L-lactate (400μM) resulted in the release of NA (+127.6 ± 14.6 V*Sec, n=15, p<0.001; paired t-test). In conclusion, activation of astrocytes results in powerful modulation of NA transmission via release of L-lactate, the cellular and molecular mechanisms of which are currently under investigation.