Selective cholinergic depletion of the hippocampus spares both behaviorally induced Arc transcription and spatial learning and memory

Hippocampus. 2007;17(3):227-34. doi: 10.1002/hipo.20261.

Abstract

We demonstrated previously that when hippocampal-dependent learning and plasticity are compromised by fornix lesions, behaviorally induced expression of the immediate early gene, Arc, is correspondingly low. The medial septum and the vertical diagonal band are major sources of subcortical afferents that innervate the hippocampus via the fornix. Here we assessed the specific contribution of cholinergic afferents from these regions to the impairments in spatial learning and behavioral induction of Arc transcription produced by fornix lesions. The immunotoxin, 192 IgG-saporin, was used to produce selective lesions of cholinergic cell bodies in the medial septum and vertical diagonal band. Rats were then trained on both cued and spatial delayed match-to-place tasks in a radial arm water maze. Animals with 192 IgG-saporin lesions learned both cue and place discrimination tasks in the water maze normally, and showed only a mild and transient impairment when switching from the cued to the spatial version of the task. Following behavioral testing, rats explored two novel environments sequentially in a setting known to induce Arc expression in hippocampal pyramidal neurons. In marked contrast to the effects of complete fornix transection, quantitative in situ autoradiography revealed no differences in Arc mRNA expression between sham and lesion animals in CA1, CA3 or stratum radiatum. The conclusion from these data is that cholinergic deafferentation alone cannot account for the spatial learning deficits or impaired behavioral induction of Arc transcription produced by fornix lesions.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Acetylcholine / metabolism
  • Animals
  • Antibodies, Monoclonal
  • Cholinergic Fibers / metabolism*
  • Cues
  • Cytoskeletal Proteins / genetics*
  • Denervation
  • Discrimination Learning
  • Fornix, Brain / metabolism
  • Fornix, Brain / physiopathology
  • Hippocampus / metabolism*
  • Male
  • Maze Learning / physiology*
  • Memory / physiology*
  • Memory Disorders / metabolism
  • Memory Disorders / physiopathology
  • N-Glycosyl Hydrolases
  • Nerve Tissue Proteins / genetics*
  • Pyramidal Cells / metabolism
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Long-Evans
  • Ribosome Inactivating Proteins, Type 1
  • Saporins
  • Septal Nuclei / metabolism*
  • Septal Nuclei / physiopathology

Substances

  • 192 IgG-saporin
  • Antibodies, Monoclonal
  • Cytoskeletal Proteins
  • Nerve Tissue Proteins
  • RNA, Messenger
  • Ribosome Inactivating Proteins, Type 1
  • activity regulated cytoskeletal-associated protein
  • N-Glycosyl Hydrolases
  • Saporins
  • Acetylcholine