Locus coeruleus alpha-adrenergic-mediated activation of cortical astrocytes in vivo.

The locus coeruleus (LC) provides the sole source of norepinephrine (NE) to the cortex for modulation of cortical synaptic activity in response to salient sensory information. NE has been shown to improve signal-to-noise ratios, sharpen receptive fields and function in learning, memory, and cognitive performance. Although LC-mediated effects on neurons have been addressed, involvement of astrocytes has thus far not been demonstrated in these neuromodulatory functions. Here we show for the 1st time in live mice, that astrocytes exhibit rapid Ca(2+) increases in response to electrical stimulation of the LC. Additionally, robust peripheral stimulation known to result in phasic LC activity leads to Ca(2+) responses in astrocytes throughout sensory cortex that are independent of sensory-driven glutamate-dependent pathways. Furthermore, the astrocytic Ca(2+) transients are competitively modulated by alpha(2)-specific agonist/antagonist combinations known to impact LC output, are sensitive to the LC-specific neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, and are inhibited locally by an alpha-adrenergic antagonist. Future investigations of LC function must therefore consider the possibility that LC neuromodulatory effects are in part derived from activation of astrocytes.