 Fictive sigh depends critically on synaptic mechanisms that involve P/Q type calcium channels, suggestive of a subset of neurons with specialized synapses for this type of rhythm generation, since only a very small number of respiratory neurons receive glutamatergic inputs that depend on P/Q type calcium currents.The fictive sigh rhythmic type also depends on mGluR8 receptor activation.Eupneic rhythmic activity relies on NMDA-dependent mechanisms.