Impairment of mossy fiber long-term potentiation and associative learning in pituitary adenylate cyclase activating polypeptide type I receptor-deficient mice - PubMed (original) (raw)
. 2001 Aug 1;21(15):5520-7.
doi: 10.1523/JNEUROSCI.21-15-05520.2001.
Y Kovalchuk, D P Wolfer, P Gass, M Martin, W Zuschratter, H J Gröne, C Kellendonk, F Tronche, R Maldonado, H P Lipp, A Konnerth, G Schütz
Affiliations
- PMID: 11466423
- PMCID: PMC6762677
- DOI: 10.1523/JNEUROSCI.21-15-05520.2001
Impairment of mossy fiber long-term potentiation and associative learning in pituitary adenylate cyclase activating polypeptide type I receptor-deficient mice
C Otto et al. J Neurosci. 2001.
Abstract
The pituitary adenylate cyclase activating polypeptide (PACAP) type I receptor (PAC1) is a G-protein-coupled receptor binding the strongly conserved neuropeptide PACAP with 1000-fold higher affinity than the related peptide vasoactive intestinal peptide. PAC1-mediated signaling has been implicated in neuronal differentiation and synaptic plasticity. To gain further insight into the biological significance of PAC1-mediated signaling in vivo, we generated two different mutant mouse strains, harboring either a complete or a forebrain-specific inactivation of PAC1. Mutants from both strains show a deficit in contextual fear conditioning, a hippocampus-dependent associative learning paradigm. In sharp contrast, amygdala-dependent cued fear conditioning remains intact. Interestingly, no deficits in other hippocampus-dependent tasks modeling declarative learning such as the Morris water maze or the social transmission of food preference are observed. At the cellular level, the deficit in hippocampus-dependent associative learning is accompanied by an impairment of mossy fiber long-term potentiation (LTP). Because the hippocampal expression of PAC1 is restricted to mossy fiber terminals, we conclude that presynaptic PAC1-mediated signaling at the mossy fiber synapse is involved in both LTP and hippocampus-dependent associative learning.
Figures
Fig. 1.
Generation of PAC1-deficient mice.a, Organization of PAC1 encompassing exons 7–13. We flanked exon 11 (black box) with loxP sites in two steps. First, we generated the modified allele by homologous recombination in ES cells. Second, transient expression of Cre recombinase led to removal of the selection cassette, generating_PAC1_ − and_PAC1_loxP alleles. A scheme of the wild-type locus, the targeting vector, and the resulting alleles is depicted (black triangles, loxP;K, _Kpn_I; X,Xba_I; A and B represent probes outside of the homology arms used for Southern blot analysis of electroporated ES cells). b, c, RNase protection analysis of total brain RNA from wild-type (wt) and PAC1−/−mice. b, Although the 400 bp wild-type transcript is absent in PAC1−/− brains, a faint 340 bp fragment is detectable, representing an alternatively spliced transcript giving rise to a truncated receptor protein.c, PACAP type II receptors (VPAC1 and VPAC2) are not upregulated in PAC1−/− brains (M, 1 kb ladder). d–f, In situ hybridization of control, PAC1_−/−, and PAC1CaMKCre2 brains. In comparison with control (d), PAC1 mRNA is almost completely absent in the hippocampal region of PAC1CaMKCre2 brains (f) and also not detectable in PAC1−/− brains (e).
Fig. 2.
Mossy fiber LTP is impaired in PAC1−/− mice. a,b, LTP summary graphs in wild-type (white circles; mean ± SEM; 5 cells) and PAC1−/− (black circles; 7 cells) mice. Insets above show sample traces of EPSCs before (control), 30 min after tetanization (30 min), and after 1 μ
m
DCG-IV bath application (+ DCG IV) in wild-type (a, WT) and PAC1−/− (b, PAC1 − /−) mice. LTP was induced by a stimulus train lasting for 5 sec at 25 Hz that was delivered at time 0. Each current trace is an average of 9–15 consecutive records. All recordings were done at room temperature (21–25°C). c, d, Different representation of the graphs shown in a and_b_ to stress the similarity of PTP (c) and the difference in LTP (d) in wild-type and PAC1−/− mice, respectively. Note that the y_-axes were scaled differently in_c and d. The two solid lines in c represent exponential fits for the first 10 min of the decay phase of PTP yielding a time constant of τ = 3.57 min (WT, left panel graph) and τ = 3.22 min (PAC1 − /− , right panel graph). All recordings were done at room temperature (21–25°C).
Fig. 3.
Preservation of LTP at the perforant path synaptic inputs to hippocampal granule cells in PAC1−/− mice. a, LTP summary graph in wild-type (white circles; mean ± SEM; 6 cells) and PAC1−/−(black circles; 6 cells) mice. Inset_illustrates sample EPSC traces before (control) and 40 min after LTP induction (40 min) in wild-type (WT, top traces) and PAC1−/−(PAC1 − /− , bottom traces) mice. Each current trace is an average of 9–15 consecutive records. LTP was induced by five 100 msec lasting stimulation trains at 100 Hz separated by 15 sec intervals, while the cell was current-clamped at −50 mV. Recordings were done at 30–32°C. b, Summary graph (mean ± SD) of the magnitude of LTP in wild-type (white bars) and PAC1−/− (black bars) mice examined in mossy fiber to CA3 pyramidal cell synapses (MF-LTP, from data shown in Fig.2_a,b) and lateral perforant path to granule cell synapse (PP-LTP, from data shown in Fig. 3_a_). A significant change was observed only for MF-LTP (*p< 0.001). MF-LTP was measured at room temperature (21–25°C), whereas PP-LTP was measured at 30–32°C (see Materials and Methods).c, Summary graph (mean ± SD) of the magnitude of paired-pulse facilitation (MF-PPF) and post-tetanic potentiation (MF-PTP) at mossy fiber to CA3 pyramidal cell synaptic inputs from wild-type (white bars; n = 5) and PAC1−/− (black bars; n = 7) mice. There was no significant difference between wild-type and mutant mice. Recordings were done at room temperature (21–25°C).
Fig. 4.
PAC1−/−mice do not display any memory deficits in declarative learning tasks.a, Acquisition phase of the Morris water maze. The average values of two daily trials over a training period of 2 weeks are depicted. Wild-type (n = 28; broken line) and PAC1−/−(n = 28; solid line) as well as PAC1CaMKCre2 mice (data not shown) learn the task equally well, as evidenced by the reduction of time needed to find the platform at the end of the training period. b, Probe trial of the Morris water maze. Wild types (white bars) and mutants (black bars) have learned and remember the old platform position equally well. In search of the platform, they spend significantly more time in the trained quadrant (T) than on average in the other three quadrants (N). c, Social transmission of food preference. PAC1−/− as well as PAC1CaMKCre2 mice (data not shown) do not display any memory deficits in the social transmission of food preference. Mutants (n = 28; black bars) and wild types (n = 28; white bars) eat significantly more of the cued than of the non-cued food and thus remember exactly the food eaten by the demonstrator mouse 24 hr before.
Fig. 5.
PAC1−/−and PAC1CaMKCre2 mice show a selective deficit in hippocampus-dependent associative learning. PAC1−/− mice [n = 14 mutants (black bars), 14 wild types (white bars); p < 0.005] as well as PAC1CaMKCre2 mice [n = 12 mutants (gray bars), 20 wild types (white bars); p < 0.01] exhibit a strongly reduced freezing response in contextual but not cued fear conditioning (24 hr test).
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