Impaired learning and memory and altered hippocampal neurodevelopment resulting from interleukin-2 gene deletion

• Published in: Journal of neuroscience research Vol. 56; no. 4; pp. 441 - 446
• Main Authors: Petitto, John M., McNamara, Robert K., Gendreau, Paul L., Huang, Zhi, Jackson, Amy Jo
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 15.05.1999
• Subjects: Acoustic Stimulation; Animals; autoimmunity; behavior; cytokines; Fear; Gene Deletion; Hippocampus - abnormalities; Hippocampus - growth & development; immunodeficiency; Interleukin-2 - genetics; knockout; Learning; Maze Learning; Memory; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, SCID; Mossy Fibers, Hippocampal - abnormalities; Mossy Fibers, Hippocampal - growth & development; Motor Activity; Reflex, Startle; Space Perception
• ISSN: 0360-4012; 1097-4547
• DOI: 10.1002/(SICI)1097-4547(19990515)56:4<441::AID-JNR11>3.0.CO;2-G

Interleukin‐2 (IL‐2), the protypical T cell growth factor and immunoregulatory cytokine produced by lymphocytes, has been implicated as a brain neurotrophic factor and neuromodulator. The consequences of the absence of endogenous IL‐2 on brain development and function were unknown. Brain IL‐2 receptors are enriched in the hippocampal formation, an area critical for the acquisition and consolidation of spatial learning and memory. Thus, we tested the hypothesis that mice lacking IL‐2 would exhibit alterations in hippocampal‐dependent learning and neurodevelopment. Compared with C57BL/6‐IL‐2+/+ wild‐type mice, we observed that C57BL/6‐IL‐2−/− gene knockout mice had markedly impaired spatial learning and memory in the Morris water maze. No significant deficits in parameters of learning and memory performance were found in severe combined immunodeficient (SCID) mice (C57BL/6scid), however, suggesting that the impaired spatial learning and memory exhibited by IL‐2 knockout mice is not attributable to generalized immunodeficiency resulting from the absence of endogenous IL‐2. Examination of other domains of behavioral performance showed that the IL‐2 knockout and wild‐type mice did not differ in measures of fearfulness or locomotor activity in an elevated plus maze, or in reflexive startle responses to auditory stimuli—although prepulse inhibition of acoustic startle (PPI) was increased significantly in IL‐2 knockout mice. The spatial learning and memory impairment in IL‐2 knockout mice was accompanied by reductions in hippocampal infrapyramidal mossy neuronal fiber length, a factor shown previously to correlate positively with spatial learning ability. These findings indicate that, in addition to being a pivotal cytokine in immune regulation, IL‐2 may play a role in the development and regulation of brain neurons involved in spatial learning and memory. J. Neurosci. Res. 56:441–446, 1999. © 1999 Wiley‐Liss, Inc.