Influence of membrane properties on coupling efficacy. (A) Morphological representation of two coupled MesV neurons from mouse (left) and rat (right). Note that in addition to the connections between their somata in both species, an axon–axon communication (black arrow) can also be observed in the case of the rat. (B) Graphical summary of the main differences and similarities of the electrophysiological properties of the gap junctions between both species. Top: To test for coupling strength, spike transmission and postsynaptic recruitment current pulses are injected in one of the cells (presynaptic) to elicit hyperpolarization of the membrane and action potentials. Firing threshold was more depolarized in mice MesV neurons, and the amplitude of their spike and AHP was smaller. The resting membrane potential is similar in both species. Middle: Membrane mechanisms. Higher density of gap junctions in the mouse than the rat (symbolized by hexomeric connexin complexes in green). Greater K+ type D (ID) current in the mouse (due to a higher number of K+ channels for ID or changes in the channel conductance) and equal conductance for K+ type A (IA) current and persistent sodium (INAP) current in both species. Bottom: Responses recorded in the second cell (postsynaptic) following current pulse injections in the first show similar coupling strength when measured passively with hyperpolarizing responses and similar amplitude of elicited spikelets, but a higher efficacy in postsynaptic recruitment in the rat.