?isoform-selective changes in PKC immunoreactivity after trace eyeblink conditioning in the rabbit hippocampus

Abstract

An immunocytochemical examination of the rabbit hippocampus was done to determine which of the Ca 21 -dependent protein kinase C (PKC) isoforms (PKCa, -bI, -bII, or -g) are involved in associative learning. The hippocampally dependent trace eyeblink conditioning task was used for behavioral training, and pseudoconditioned and naive animals served as controls. Significant increases (P F 0.05) in staining intensity were found with antibodies reactive with the catalytic or the regulatory domain of PKCg in conditioned animals compared with naive and pseudoconditioned subjects at a 24-h post-conditioning time point. The increase was found in CA1 and CA3 pyramidal cell bodies, in apical dendrites and the proximal part of the basilar dendrites, and in cell bodies of dentate granule cells. In contrast, no conditioning-specific changes were found for PKCa, -bI, or -bII in hippocampal neurons. The increase in PKCg immunoreactivity (ir) was significantly less (P F 0.05) in poor learners than in good learners. The correlation between the degree of PKCg-ir and the total number of conditioned responses across training sessions was both positive and significant. These results suggest that PKCg is the major Ca 21 -dependent PKC isoform involved in hippocampal neurons during acquisition of associative memories. Immunoblots revealed no conditioning-induced increase in the total amount or translocation of PKCg at the 24-h time point, and no proteolytic PKC fragments were observed. In agreement with the Western blot data, PKC activity did not differ among naive, pseudoconditioned, and trace conditioned animals. The conditioning-induced increase in antibody binding to the g-isoform must therefore be due to an increased access to the antigenic site(s) as a result of alteration in the tertiary structure of PKCg or in quaternary interactions of PKCg in situ.

Learning-related postburst afterhyperpolarization reduction in CA1 pyramidal neurons is mediated by protein kinase A

“…Increase in membraneassociated PKC has been demonstrated in the hippocampus and cerebellum of rabbits after learning EBC (31)(32)(33). However, a decrease in membrane-associated PKC has also been shown in the hippocampus after spatial learning in rats and mice (34)(35)(36).…”

Experience on the Barnes Spatial Maze Influences PKCγ Levels in the Hippocampus

“…The extent of spatial memory impairment among aged rats correlates negatively with levels of PKCγ in hippocampal homogenates measured by quantitative western blotting (Colombo, Wetsel, & Gallagher, 1997). Studies by Van Der Zee, Compaan, de Boer, and Luiten (1992) and Van Der Zee, Kronforst-Collins, Maizels, Hunzicker-Dunn, and Disterhoft (1997) have shown that immunoreactivity for PKCγ increases in the hippocampus following spatial learning. Additionally, activation of PKCγ by agonists prior to fear conditioning training result in significantly improved learning and increased hippocampal membrane-bound PKCγ (Smith & Wehner, 2002).…”

Neurotoxic lesions of the dorsal hippocampus disrupt auditory-cued trace heart rate (fear) conditioning in rabbits

“…Other paradigms like trace eyeblink conditioning require many more days of training (i.e., 7-14 days), and therefore have been more difficult for in vivo tracking of single neuron activity across acquisition (e.g., McEchron and Disterhoft, 1997). It may also be convenient to use the trace fear model for other types of experiments where trace eyeblink conditioning has been used in the past, e.g., examining the learning-related changes in the biophysical properties of hippocampal neurons in vitro (e.g., , and examining the learning-related changes in the biochemical properties of hippocampal neurons (e.g., Van der Zee et al, 1997). Another advantage of trace HR conditioning is that the time course of the HR index can be measured over a long 10-s trace conditioning trial.…”