Postsynaptic potentials and morphological features of tectal cells in homing pigeons

In this study postsynaptic potentials responding to the electrical stimulation of the optic nerve and the nucleus isthmi pars parvocellularis (Ipc) were intracellularly recorded from 86 tectal cells in pigeons, 13 of which were marked with Lucifer yellow (LY). According to types of postsynaptic potentials and their succession, the postsynaptic responses could be classified into four types: excitatory postsynaptic potential (EPSP)-inhibitory postsynaptic potential (IPSP) sequence (EI type), E, I and IE types. Among them, E or EI responses were mainly produced to the optic nerve stimulation, while the electrical stimulation of the Ipc elicited I responses in more than half the recorded cells. LY-marked tectal cells included five ganglionic cells, four pyramidal cells, two bipolar cells and two stellate cells. The ganglionic cells were mainly located in tectal layers III and IV, whereas the others were in layer II. It appears from both intracellular recordings and fluorescent markings that there is some correlation between the morphological features and the postsynaptic response types of tectal cells.