GAP-JUNCTIONS COUPLE ASTROCYTES BUT NOT NEURONS IN DISSOCIATED CULTURES OF RAT SUPRACHIASMATIC NUCLEUS

Individual neurons dissociated from rat suprachiasmatic nucleus can ex press independently phased circadian firing rhythms in culture. The ph ases of these rhythms are unperturbed by reversible blockade of neuron al firing lasting 2.5 days, indicating that multiple circadian clocks continue to operate in the absence of conventional synaptic transmissi on. The possibility remains, however, that these circadian rhythms mig ht depend on some other form of intercellular communication. In the pr esent study, a potential role for gap junctional coupling in SCN cultu res was evaluated by introduction of the tracer molecule Neurobiotin i nto both neurons (n = 98) and astrocytes (n = 10), as well as by immun olabeling for specific connexins, the molecular components of gap junc tions. Astrocytes were extensively coupled to each other by connexin43 -positive gap junctions, but no evidence was found for coupling of neu rons to each other or to astrocytes. These data support the hypothesis that neurons expressing independently phased circadian rhythms in SCN cultures ('clock cells') are autonomous, single cell circadian oscill ators, but do not exclude a role for glia in synchronizing neuronal cl ock cells in vivo.