Place navigation in rats with unilateral tetrodotoxin inactivation of the dorsal hippocampus: Place but not procedural learning can be lateralized to one hippocampus.

Abstract

Lateralization of the Morris water maze task was examined by injecting 5 ng of tetrodotoxin (TTX) into one dorsal hippocampus (HPC) of chronically cannulated rats (n = 20). The task, acquired (A) during unilateral HPC block, was retrieved (R) during TTX blockade of the ipsi- (I) or contralateral (C) HPC. Escape latencies (in seconds) at 3 levels of acquisition and in the first 4-trial block of I or C retrieval suggest lateralization was absent after the first block (A = 49, I = 40, C = 44), partial after training to an efficient search strategy (A = 6, I = 9, C = 14), and complete after overtraining to goal-directed escape (A = 4, I = 4, C = 12), as further indicated by comparisons of A vs. R behavior and probe trials. The analyses also indicate that (a) HPC contributes to the acquisition but is unnecessary for retrieval of the procedural engram, (b) overtrained learning with one HPC or intact brain is similar, and (c) there is no left-right hemispheric specialization for place learning.

Beyond Memory, Navigation, and Inhibition: Behavioral Evidence for Hippocampus-Dependent Cognitive Coordination in the Rat

“…TTX injection did not impair (Room&Arena)ϩ avoidance or water-maze learning (Fenton et al, 1993;Kubik et al, 2004), analogous to reports that patients do not manifest cognitive coordination deficits when stimuli have strong prepotent organization. The TTX injection improved Arenaϩ avoidance, analogous to reports that schizophrenics identify stimuli better than controls when the gestalt processes of controls are activated (Place and Gilmore, 1980;Silverstein et al, 1996).…”

“…Intrahippocampal injections of saline or 5 ng of TTX dissolved in 1 l of saline were made through one guide cannula during 1 min (Zhuravin and Bureš, 1991;Fenton and Bureš, 1993;Fenton et al, 1995;Cimadevilla et al, 2001). A habituating TTX injection was given 1 week after surgery, and the rats were observed for signs of ataxia, but none were observed, suggesting proper cannula placement, which was confirmed histologically after testing (Fig.…”

“…Injecting tetrodotoxin (TTX) into both hippocampi confirmed the task was hippocampus dependent (Cimadevilla et al, 2000a). Unilateral hippocampal dysfunction spared learning in other spatial tasks (Olton et al, 1982;Sutherland et al, 1983;Fenton and Bureš, 1993;Fenton et al, 1995;Moser and Moser, 1998), and we wanted to confirm this for place avoidance as a basis for studying how information is organized between the hippocampi. Injecting TTX into one dorsal hippocampus unexpectedly abolished learning, consolidation, and retrieval of place avoidance on the rotating arena (Cimadevilla et al, 2001).…”

Left–right dissociation of hippocampal memory processes in mice

“…Unilateral hippocampal lesions in mice have not revealed a distinct hemispheric contribution to long-term memory (25), although split-brain mice with left eye deprivation showed greater spatial memory accuracy than those with right eye deprivation when the environmental complexity increased (26). Studies in rats have either shown no effect of unilateral lesions (27,28) or no asymmetry of hippocampal function (27,29), or have produced inconsistent findings (30)(31)(32). However, the chronic nature of surgical, and even pharmacological, manipulations can allow compensatory changes to develop.…”

Behavioral Evidence That Segregation and Representation Are Dissociable Hippocampal Functions

“…The methods for surgical implantation of guide cannulas and the infusion of TTX have been described previously in detail (Fenton and Bureš, 1993;Fenton et al, 1995;Cimadevilla et al, 2000Cimadevilla et al, , 2001Klement et al, 2005;Wesierska et al, 2005). Rats were anesthetized (50 mg/kg Nembutal; Sigma, St. Louis, MO), and the skull was exposed.…”