According to astrocyte-neurone lactate shuttle hypothesis, lactate released from astrocytes, is used by neurones as preferred metabolic substrate (Pellerin and Magistretti, 1994). Here, we used optogenetics to investigate signalling between astrocytes and noradrenergic neurones of the locus coeruleus (LC). In organotypic slice cultures of Wistar rat pups containing LC astrocytes were transduced with an AVV (Adenoviral vectors) to express a mutant version of the light sensitive channel rhodopsin 2 (ChR2-H134R33) fused with a far- red shifted fluorescent protein mKate and NAergic neurons were targeted to express DsRed2 with AVV-PRS8-Dsred (Gourine et al., 2010). Patch clamp recordings were made from DsRed2-positive neurones in LC. Activation of astrocytes with blue light evoked long lasting depolarisations of adjacent LC neurones (depolarisation + 3.08 ± 0.33 mV, n=14). This depolarisation could be blocked by an inhibitor of glycogen breakdown, 1,4-dideoxy-1,4-imino-D-arabinitol (DAB; 500 μM, pre-incubation 1h, depolarisation + 0.96 ± 0.15 mV, n=5, p<0.001) or D-lactate (2mM; +1.27± 0.38 mV, n=5, p<0.01) but not with the inhibitor of monocarboxylate transporters 4-CIN (100 μM, +2.9± 0.46mV,n=4, p>0.05). In the other set of experiments we applied fast scan cyclic voltammetry (FCV) to measure noradrenalin (NA) release from LC neurones in organotypic slices. To selectively stimulate Gs-protein-mediated signalling cascade in astrocytes, we used AVV to express rhodopsin chimera with β2 adrenergic receptors (optoβ2AR; Airan et al., 2009). Light activation of optoβ2AR-expressing astrocytes resulted in a clear increase in noradrenalin release (83.23 ± 10.6 mM*Sec, n=32), which again was abolished by DAB (500 μM, 0.75 ± 7.35 mM*Sec, n=6, p<0.001) and D-lactate (400 μM, -0.59±1.107mM*Sec, n=8, p <0.001). This was interpreted as evidence for the involvement of L-lactate in this effect. To confirm that optoβ2AR can trigger L-lactate production in astrocytes, we measured pH with SNARF-5AM in primary dissociated glial cultures and found that light simulation resulted in the emission ratio shift, indicative of acidification (144.4% ± 2.206%, n=58) which could be blocked by pre-incubation with DAB (101.3±0.6872%, n=32, p <0.001). These experiments imply that activation of astrocytes excites LC neurons and potentiates NA release via release of L-lactate. The mechanism by which L-lactate modulates neuronal activity is currently under investigation.