Glucose Injections into the Dorsal Hippocampus or Dorsolateral Striatum of Rats Prior to T-Maze Training: Modulation of Learning Rates and Strategy Selection

• Published in: Learning & memory (Cold Spring Harbor, N.Y.) N.Y.), 2005-07, Vol.12 (4), p.367-374
• Main Authors: Canal, Clinton E, Stutz, Sonja J, Gold, Paul E
• Format: Article
• Language: English
• Subjects: Anatomical correlates of behavior; Animal; Animals; Behavior Modification; Behavior, Animal - drug effects; Behavioral psychophysiology; Biochemistry; Biological and medical sciences; Brain; Brain Hemisphere Functions; Corpus Striatum - drug effects; Corpus Striatum - physiology; Experimental Psychology; Fundamental and applied biological sciences. Psychology; Glucose - pharmacology; Hippocampus - drug effects; Hippocampus - physiology; Learning; Learning. Memory; Male; Maze Learning - drug effects; Microinjections; Molecular Biology; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Rats; Rats, Sprague-Dawley; Research Papers; Responses; Spatial Ability; Task Analysis
• ISSN: 1072-0502; 1549-5485
• DOI: 10.1101/lm.88205

The present experiments examined the effects of injecting glucose into the dorsal hippocampus or dorsolateral striatum on learning rates and on strategy selection in rats trained on a T-maze that can be solved by using either a hippocampus-sensitive place or striatum-sensitive response strategy. Percentage strategy selection on a probe trial (P[subscript crit]) administered after rats achieved criterion (nine of 10 correct choices) varied by group. All groups predominately exhibited a response strategy on a probe trial administered after overtraining, i.e., after 90 trials. In experiment 1, rats that received intrahippocampal glucose injections showed enhanced acquisition of the T-maze and showed increased use of response solutions at P[subscript crit] compared with that of unimplanted and artificial cerebral spinal fluid (aCSF)-treated groups. These findings suggest that glucose enhanced hippocampal functions to accelerate the rate of learning and the early adoption of a response strategy. In experiment 2, rats that received intrastriatal glucose injections exhibited place solutions early in training and reached criterion more slowly than did aCSF controls, with learning rates comparable to those of unoperated and operated-uninjected controls. Relative to unoperated, operated-uninjected and glucose-injected rats, rats that received intrastriatal aCSF injections showed enhanced acquisition of the T-maze and increased use of response solutions at P[subscript crit]. The unexpected enhanced acquisition seen after striatal aCSF injections suggests at least two possible interpretations: (1) aCSF impaired striatal function, thereby releasing competition with the hippocampus and ceding control over learning to the hippocampus during early training trials; and (2) aCSF enhanced striatal functioning to facilitate striatal-sensitive learning. With either interpretation, the results indicate that intrastriatal glucose injections compensated for the aCSF-induced effect. Finally, enhanced acquisition regardless of treatment was accompanied by rapid adoption of a response solution for the T-maze. (Contains 9 figures.)