During stepwise cue deletion, rat place behaviors correlate with place unit responses.

The place behaviors of intact rats, and of those receiving fornix lesions, were examined in the radial-arm maze. A cue-restricted environment was constructed wherein the location of arms with food rewards were identifiable only by their position in relation to an intermittently rotated 4-cue set. Food obtainment was measured during a procedure in which either 1, 2 or 3 of the cues were removed during a block of test sessions. Control animals demonstrated place navigation abilities robust to the deletion of any 1 or 2 cues. The performance of lesioned rats declined in a manner consistent with the number of absent stimuli. The results indicate that the behavioral expressions of place knowledge relate to the responsiveness of hippocampal place cells.

Alteration in adenylate cyclase response to aminergic stimulation following neonatal x-irradiation.

X-irradiation of the rat neonatal hippocampus produces severe alterations in the architectonic features of the mature hippocampus. The most prominent alterations is a marked depletion of the granule cells of the dentate gyrus, with a subsequent realignment of CA 4 cells. The present data also show that norepinephrine (NE), dopamine and histamine stimulation of adenylate cyclase activity is severely attenuated in the hippocampi of irradiated animals. This failure suggests that the NE fibers of irradiated subjects, although normal in content of NE, are not functional in some of their NE-effector actions.

Origin of the neocortically monitored theta rhythm in the curarized rat.

An array of epidural electrodes was acutely implanted in locally anesthetized, curarized rats in order to map the surface distribution of rhythmic slow activity (RSA) which appears within the neocortex. Peak amplitudes (of about 122 muV) were centered over the dorsal hippocampus outline. A laminar profile of RSA recorded within the neocortex indicated no shifts in phase relative to a homotopic, epidural electrode. RSA increased slightly in amplitude (mean increase = 53%) at the deepest level or neocortex, but it did not approximate an amplitude peak or null within the neocortex. Multiple-unit activities within the neocortex were not phase-locked to RSA. On the other hand, all of these manifestations of an RSA generator were observed as electrodes passed into the dorsal hippocampus. A unilateral cortical spreading depression (CSD) treatment, which markedly attenuated barbiturate spindles in all subjects (N = 10), usually (N = 7 of 10) had no effect on the neocortically monitored RSA. Dissociations between depressed and non-depressed hemispheres, and between neocortical and hippocampal RSA, were obtained in some subjects during CSD. However, concurrent dissociations were also apparent between recording sites within the hippocampus. It is concluded that the neocortical RSA of rats is passively spread from the underlying hippocampus, and dissociations in neocortical and hippocampal RSA in the rat are secondary to changes in the organization of multiple generators of hippocampal RSA.

Memory: proline induces retrograde amnesia in chicks.

Intracerebral injection of L-proline, 1 minute after one-trial avoidance training of chicks, impaired memory 24 hours later. Chicks injected with proline 1 or 4 hours after training and controls injected with L-isoleucine at intervals after training, showed no impairment of memory 24 hours after training. The retrograde impairment of long-term memory induced by proline occurred without the convulsions or electrographic events usually associated with retrograde amnesic treatments.