Figure 5.

Neurochemical identification of slow and rhythmic firing septal neurons after hippocampal injections. A, C, Examples of juxtacellular labeling in vivo under anesthesia of rhythmic (A) and slow (C) firing septal neurons from vehicle (top) and Aβ-treated (bottom) rats that were recorded during θ hippocampal activity, identified by neurobiotin staining, and counterstained for ChAT and GAD. A, two rhythmic GABAergic parvalbumin-positive neurons. C, A cholinergic neuron in a vehicle-treated rat and a GABAergic neuron in one Aβ-treated rat. Scale bars, 20 μm. B, D, Corresponding spike activity and hippocampal LFP epochs. E, Histograms of autocorrelation of B traces with the corresponding rhythmicity index (RI) (see Materials and Methods). F, ChAT immunoreactivity in the medial septum after hippocampal Aβ injection. Shown is an example of analyzed sections of the medial septum-diagonal band corresponding to the major part of the vertical limb (0.6 mm² fields, >60% of medial septum-diagonal band between level 9.7 and 9.3 anterior to the interaural level) from vehicle-treated (left) and Aβ-treated rats (right). Scale bar, 200 μm. G, Parvalbumin immunoreactivity in the medial septum from vehicle-treated (left) and Aβ-treated rats (right). Scale bar, 200 μm. Hippocampal Aβ injections induced a reduction in GABAergic cell rhythmic firing rate and an increase in the probability for slow-firing cells to display GAD immunoreactivity in the absence of cell loss in the medial septum (see also supplemental Table 1, available at www.jneurosci.org as supplemental material).