Evidence for electrical synapses between neurons of the nucleus reticularis thalami in the adult brain in vitro

It has been demonstrated in juvenile rodents that the inhibitory neurons of the nucleus reticularis thalami (NRT) communicate with each other via connexin 36-based electrical synapses. However, whether functional electrical synapses persist into adulthood is not fully known. Here we show that in the presence of the metabotropic glutamate receptor agonists, either trans-ACPD (100 mM) orDHPG (100 mM), 15% of neurons in slices of the adult cat NRT maintained in vitro exhibit stereotypical spikelets with several properties that indicate that they reflect action potentials that have been communicated through an electrical synapse. In particular, these spikelets (1) display a conserved, all-or-nothing waveform with a pronounced after-hyperpolarization (AHP), (2) exhibit an amplitude and time to peak that are unaffected by changes in membrane potential, (3) always occur rhythmically with the precise frequency increasing with depolarization, and (4) are resistant to blockers of conventional, fast, chemical synaptic transmission. Thus, these results indicate that functional electrical synapses in the NRT persist into adulthood where they are likely to serve as an effective synchronizing mechanism for the wide variety of physiological and pathological rhythmic activities displayed by this nucleus.