Changes in hippocampal theta following intrahippocampal corticotropin-releasing hormone (CRH) infusions in the rat

• Published in: Brain research bulletin Vol. 48; no. 6; pp. 603 - 607
• Main Authors: Kortekaas, Rudie, Costall, Brenda, Smythe, James W
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.04.1999; Elsevier Science
• Subjects: Acetylcholine; Analysis of Variance; Animals; Behavioral psychophysiology; Biological and medical sciences; Corticotropin-Releasing Hormone - pharmacology; CRH; Electrophysiology; Fundamental and applied biological sciences. Psychology; Hippocampus; Hippocampus - drug effects; Hippocampus - physiology; Hypothalamic-pituitary-adrenal axis; Injections; Male; Memory; Pharmaceutical Vehicles - pharmacology; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Rat; Rats; Rats, Inbred Strains; Stress; Theta; Theta Rhythm - drug effects; Rat; Memory; CRH; Hypothalamic-pituitary-adrenal axis; Acetylcholine; Hippocampus; Theta; Stress; Hypothalamohypophysoadrenal axis; Rodentia; Central nervous system; Corticotropin releasing factor; Electrophysiology; Electroencephalography; Hypothalamic hormone; Vertebrata; Mammalia; Animal; Theta rhythm; Hormone releasing factor; Brain (vertebrata)
• ISSN: 0361-9230; 1873-2747
• DOI: 10.1016/S0361-9230(99)00039-8

Hippocampal theta activity is a large amplitude, sinusoidal wave that occurs during attentive immobility and exploratory behaviour in the rat, and it is thought to be involved in memory formation. Recent reports suggest that corticotropin-releasing hormone (CRH) has pro-mnemonic effects in rodents. Because memory-enhancing substances/manipulations generally alter either theta frequencies or amplitudes, these variables were monitored in urethane-anaesthetised rats following intra-hippocampal infusions of CRH. Adult male, Lister hooded rats were implanted with a hippocampal recording electrode and a guide cannula, both aimed at the dentate gyrus. When CRH was infused into the hippocampus, the main change in the hippocampal EEG was a slow onset increase in the amplitude of spontaneous theta and, paradoxically, a significant decrease in the amount of time spent displaying theta. These data suggest that CRH has the ability to modulate ongoing hippocampal theta, but, considering the slow effect, the involvement of hippocampal CRH receptors is suspect. Regardless of locus, the described electrophysiological changes suggest that hippocampal cholinergic systems may play a role in the memory-enhancing effects of CRH.