Ten male Long-Evans (5–8 months old) and 2 male Sprague-Dawley rats (350–500g; 5–8 months) were used in these experiments. Behavioral training, surgery details and data obtained from subgroups of the present rats have been reported earlier (Csicsvari et al., 2002; Diba and Buzsaki, 2007 (link); Montgomery et al., 2009 (link); Mizuseki et al., 2009 (link)). After maze training, recording and stimulation electrodes were implanted. In six rats, a 96-site silicon probe was implanted in the right hemisphere parallel to the transverse axis of the hippocampus (45° parasagittal). These probes had recording sites spaced regularly over a 1.5mm × 1.5mm area with 6 shanks spaced at 300 μm, each with 16 recording sites at 100μm spacing. A bipolar stimulating electrode was implanted into the angular bundle (perforant path) at AP 1.0 mm, ML 1.0 mm from the junction between lambda and the right lateral ridge and DV 3.5 mm from the dura. Another stimulating electrode was implanted in the ventral hippocampal commissure at AP 1.2mm, ML 1.0mm from bregma and 3.8mm from the dura (Csicsvari et al., 2000 (link); Montgomery et al., 2009 (link)). Three other rats were implanted with 32- and/or 64-site silicon probes in the left or right dorsal hippocampus. The silicon probes, consisting of 4 or 8 individual shanks (spaced 200 μm apart) each with 8 staggered recording sites (20 μm spacing), were lowered to CA1, CA3 pyramidal cell layers (Diba and Buzsaki, 2007 (link)) and dentate gyrus. Additional 3 rats were implanted with a 4-shank silicon probe in the right dorsocaudal medial entorhinal cortex (EC; Hafting et al., 2005) and another 4- or 8-shank probe into the CA1-dentate axis (Mizuseki et al., 2009 (link)). All silicon probes were attached to a microdrive, which allowed precise positioning of the probe tips into the desired layer. Two stainless steel screws inserted above the cerebellum were used as indifferent and ground electrodes during recordings.
Postmortem electrode location was verified using thionin, fluorescent Nissl (Invitrogen), or DAPI (Invitrogen) staining in combination with DiI (Invitrogen)-labeled electrode tracks. The histological reconstruction of the electrode tracks is available in Montgomery et al. (2008; 2009) (link). All protocols were approved by the Institutional Animal Care and Use Committee of Rutgers University.
Postmortem electrode location was verified using thionin, fluorescent Nissl (Invitrogen), or DAPI (Invitrogen) staining in combination with DiI (Invitrogen)-labeled electrode tracks. The histological reconstruction of the electrode tracks is available in Montgomery et al. (2008; 2009) (link). All protocols were approved by the Institutional Animal Care and Use Committee of Rutgers University.
