Research reportAltered behavioural response to acute stress in mice lacking cellular prion protein
Introduction
Cellular prion protein (PrPc) is a glycoprotein anchored to the outer cell surface which has been highly conserved during evolution. It is expressed predominantly in neurons and, to a lesser extent, in other types of cells [1], [2], [3], [4], [5], [6]. An alteration in its secondary structure leads to accumulation of an abnormal protein PrPsc and causes an uncommon disease known as spongiform encephalopathy [7], [8], [9].
The physiological role of PrPc, however, remains elusive. The first observations of PrPc gene ablated (Prnp0/0) mice suggested that these animals developed normally and did not show major behavioural abnormalities at baseline [10]. However, during the last 10 years, some differences in behaviour were noticed between some PrPc gene ablated mice and their respective wild-type controls [11], [12], [13], [14], [15], [16]. Interestingly, many of these differences were observed only if the animals were subjected to conditions which were different from baseline ones, such as during provoked seizures [16] or after head trauma [17].
The differences between diverse PrPc null mice strains and their controls have been better studied at the cellular or subcellular level. It has been demonstrated, for example, that PrPc-deficient cells show an altered response to oxidative stress [18], [19], [20], [21], present increased levels of oxidative stress markers [20], and show imbalances in antioxidant defence [22]. Absence of PrPc also leads to altered calcium [23], zinc, [24] and copper [25] homeostasis, which might explain some of the differences in oxidative stress. Furthermore, lack of PrPc expression results in minor morphological alterations such as differences in mitochondrial numbers and morphology [26] and in hippocampal mossy fibers [27].
Based on these observations, some authors proposed physiological roles for PrPc in the regulation of oxidative stress, as well as in cell survival, signal transduction and neural excitability [1], [28], [29], [30], [31], [32]. Because of its location, anchored to the outer surface of the neurons, some authors have also suggested that PrPc may influence synaptic function as well [28], [31]. Common to several of the above cited observations is the concept that PrPc may become physiologically important when levels of functioning are different from baseline conditions. In other words, when normal homeostasis is altered, the deficits caused by the absence of PrPc may start to appear. In order to test if this might be true for behavioural tests, we evaluated the effect of acute stress on the levels of anxiety of Prnp0/0 mice. Because of additional observations during the experiments, we also evaluated the effect of physical stress on locomotor function among wild-type and Prnp0/0 mice.
Section snippets
Animals
A total of 111 adult male knockout mice (3-month-old, weighing 20–40 g) homozygous for disrupted PrPc gene, PrnP (designated Prnp0/0 mice) produced as previously described [10] were used and 118 male wild-type (Prnp+/+) mice of the same age and weight were used as controls. The Prnp0/0 mice used were descendants of Zrch I animals [10]. Wild-type controls were generated by crossing F1 descendants from a 129/Sv × C57BL/6J mating. To confirm the genotype of the animals we conduced PCR procedures with
Statistical analysis
Data for the plus-maze test (experiment 1) are presented as mean (±S.E.M.) number of entries into the open arms, number of entries into the closed arms, total number of entries, time of permanence in the open arms, time of permanence in the closed arms, and time of permanence in the center of the maze. Data for the open-field test (experiment 2) are presented as mean (±S.E.M.) number of crossings, latency to start locomotion, and latency to reach the corner. The results of the plus-maze and
Experiment 1
The first experiment was designed to determine if PrPc is involved in anxiety modulation after acute behavioural stress. First, we randomly assigned four groups of Prnp0/0 mice (n = 57) and their respective Prnp+/+ controls (n = 58) to four types of acute stress: no stress, restraint stress, foot-shock, and swimming (n = 12–15 mice/group). Immediately after the acute stress, the animals were placed in the plus-maze apparatus for the evaluation of anxiety levels (Diagram 1).
Discussion
In this study, we observed that under baseline conditions Prnp0/0 mice presented similar anxiety levels and locomotion when compared to Prnp+/+ mice. However, after either electric footshock or swimming, Prnp0/0 mice spent significantly less time in the closed arms and more time in open places in the plus-maze test than controls. This suggests that the anxiety-related behavioural reactions after acute stress observed in controls are impaired in Prnp0/0 mice. Furthermore, we observed that
Acknowledgments
Research supported by FAPESP (2003/13189-2). B. Lobão-Soares is supported by a CAPES fellowship. M.M. Bianchin is supported by FAPESP (02/03743-0). We would like to thank Dr. Charles Weissman for kindly providing the parental knockout mice to set up our breeding colony.
References (58)
- et al.
Prion protein is strongly immunolocalized at the postsynaptic domain of human normal neuromuscular junctions
Neurosci Lett
(1993) Prion protein in muscle tissue of sheep
Lancet Neurol
(2004)Prion protein found outside the CNS
Lancet Neurol
(2004)- et al.
Decreased hyperlocomotion induced by MK-801, but not amphetamine and caffeine in mice lacking cellular prion protein (PrPc)
Brain Res Mol Brain Res
(2002) - et al.
Prion protein-deficient cells show altered response to oxidative stress due to decreased SOD-1 activity
Exp Neurol
(1997) - et al.
Prion protein-deficient neurons reveal lower glutathione reductase activity and increased susceptibility to hydrogen peroxide toxicity
Am J Pathol
(1999) - et al.
The prion protein and neuronal zinc homeostasis
Trends Biochem Sci
(2003) - et al.
Ablation of cellular prion protein expression affects mitochondrial numbers and morphology
Biochem Biophys Res Commun
(2002) - et al.
Mossy fibre reorganization in the hippocampus of prion protein null mice
Brain Res
(1997) Prion and prejudice: normal protein and the synapse
Trends Neurosci
(2001)
Cellular prion protein: on the road for functions
FEBS Lett
The effects of intra-amygdala infusion of the AMPA receptor antagonist CNQX on retention performance following aversive training
Neurobiol Learn Mem
Hippocampal slices from prion protein null mice: disrupted Ca2+-activated K+ currents
Neurosci Lett
Hippocampal mossy fibres: implication in novelty reactions or in anxiety behaviours?
Behav Brain Res
The neurobiology and control of anxious states
Prog Neurobiol
Stress and cognitive function
Curr Opin Neurobiol
L-arginine uptake, the citrulline-NO cycle and arginase II in the rat brain: an in situ hybridization study.
Brain Res Mol Brain Res
The distribution of nitric oxide synthase immunoreactivity in the human brain
Neuroscience
Recent advances in prion biology
Curr Opin Neurol
Prions in skeletal muscle
Proc Natl Acad Sci USA
Extraneural pathologic prion protein
N Engl J Med
Prions
Proc Natl Acad Sci USA
Shattuck lecture-neurodegenerative diseases and prions
N Engl J Med
Prions: pathogenesis and reverse genetics
Ann NY Acad Sci
Normal development and behaviour of mice lacking the neuronal cell-surface PrP protein
Nature
Cellular prion protein ablation impairs behavior as a function of age
Neuroreport
Impaired motor coordination in mice lacking prion protein
Cell Mol Neurobiol
Prion protein is necessary for latent learning and long-term memory retention
Cell Mol Neurobiol
Normal inhibitory avoidance learning and anxiety, but increased locomotor activity in mice devoid of PrP(C)
Brain Res Mol Brain Res
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2013, Physiology and BehaviorCitation Excerpt :Mice carrying the deletion, also post-natal, of the PrP gene (PrP knockout, PrP-KO) do not show obvious alterations in lifespan and development [5–7]. However, the necessity to understand the cellular role of PrPC has led to a close inspection of PrPC involvement in the behavioral domains governing memory, learning, motor coordination and balance [8–11]. Comparative studies on the learning and memory of wild-type (WT) and PrP-KO mice of 3–5 months of age provided conflicting results.
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2012, Behavioural Brain ResearchCitation Excerpt :It is interesting to note that a previous study from Lobao-Soares et al. [18] did not report a statistical difference in the number of crossings (ambulatory behaviour) of PrP−/− mice in the open-field test. Also of interest, and in agreement with our results, are the observations by Nico et al. [25] that show a decrease in the swimming time of PrP−/− mice in which the authors used the FST as an acute stress protocol. In our hands, the tricyclic antidepressant imipramine was able to reverse the depressive-like behaviour observed for PrP−/− mice.