Passive avoidance training is correlated with decreased cell proliferation in the chick hippocampus.
One-trial passive avoidance learning (PAL), where the aversive stimulus is the bitter-tasting substance methylanthranilate (MeA), affects neuronal and synaptic plasticity in learning-related areas of day-old domestic chicks (Gallus domesticus). Here, cell proliferation was examined in the chick forebrain by using 5-bromo-2-deoxyuridine (BrdU) at 24 h and 9 days after PAL. At 24 h post-BrdU injection, there was a significant reduction in labelling in MeA-trained chicks in both the dorsal hippocampus and area parahippocampalis, in comparison to controls. Moreover, double-immunofluorescence labelling for BrdU and the nuclear neuronal marker (NeuN) showed a reduction of neuronal cells in the dorsal hippocampus of the MeA-trained group compared with controls (35 and 49%, respectively). There was no difference in BrdU labelling in hippocampal regions between trained and control groups of chicks at 9 days post-BrdU injection; however, the number of BrdU-labelled cells was considerably lower than at 24 h post-BrdU injection, possibly due to migration of cells within the telencephalon rather than cell loss as apoptotic analyses at 24 h and 9 days post-BrdU injection did not demonstrate differences in cell death between treatment groups. Cortisol levels increased in the chick hippocampus of MeA-trained birds 20 min after PAL, suggesting the possibility of a stress-related mechanism of cell proliferation reduction in the hippocampus. In contrast to hippocampal areas, the olfactory bulb, an area strongly stimulated by the strong-smelling MeA, showed increased cell genesis in comparison to controls at both 24 h and 9 days post-training.
Nikolakopoulou
A M
AM
Biological Sciences, The Open University, Milton Keynes, UK. nikolaa@ccf.org
Dermon
C R
CR
Panagis
L
L
Pavlidis
M
M
Stewart
M G
MG
D000818:Animals; D000831:Animals, Newborn; D034961:Antigens, Nuclear / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology; D001362:Avoidance Learning / Q000502:physiology*; D001973:Bromodeoxyuridine / Q000378:metabolism; D049109:Cell Proliferation; D002645:Chickens; D006624:Hippocampus / Q000502:physiology*; D007150:Immunohistochemistry; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009473:Neuronal Plasticity / Q000502:physiology*
D034961:Antigens, Nuclear; D009419:Nerve Tissue Proteins; D001973:Bromodeoxyuridine