Figure 2.
Morphology and firing properties of CA3 GCs. A, Whole-cell recorded, biocytin filled, and subsequently reconstructed CA3 GC. A1, Dendritic and axonal arborizations of a CA3 GC (DG, GC layer of the inner blade of the DG; s.rad., stratum radiatum; s.luc., stratum lucidum; s.pyr., stratum pyramidale). The black dot in the inset indicates the location of the soma of the recorded cell within the hippocampus. Note the presence of large (“giant”) terminals with filopodial extensions on the camera lucida reconstruction of the axonal arbor primarily restricted to the stratum lucidum; see also A2. A2, Light micrographs of dendritic spines (top and middle) and of a large MF-like axon varicosity (bottom; arrowheads, main axon; asterisks, filopodia). The asterisk in A1 marks the terminal whose photograph is shown in the bottom panel in A2). A3, Accommodating firing pattern of the cell shown in A1 and A2 in response to depolarizing constant current injection. A4, Accommodating firing pattern of a DG GC. B, CB and Prox1 immunoreactivity of a CA3 GCs (left) and its firing pattern (right). C, CA3 GCs form giant MF terminals in the CA3. Electron micrographs of synaptic contacts formed by the axons of two different CA3 GCs (C1–C3, respectively; C3 is a higher-magnification image of the synaptic contacts in C2). ad, Apical dendrite; b, presynaptic terminal of the labeled CA3 GC; s, postsynaptic spine that originated from the apical dendrite labeled ad. Note the multiple synaptic specializations formed on the same postsynaptic structure (arrowheads), the large number of presynaptic vesicles, and the large size of the terminals, all typical characteristics of giant MF terminals.