Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 36 (5), 979-92

Peripheral Nerve Injury Leads to Working Memory Deficits and Dysfunction of the Hippocampus by Upregulation of TNF-α in Rodents

Affiliations

Peripheral Nerve Injury Leads to Working Memory Deficits and Dysfunction of the Hippocampus by Upregulation of TNF-α in Rodents

Wen-Jie Ren et al. Neuropsychopharmacology.

Abstract

Patients with chronic pain usually suffer from working memory deficits, which may decrease their intellectual ability significantly. Despite intensive clinical studies, the mechanism underlying this form of memory impairment remains elusive. In this study, we investigated this issue in the spared nerve injury (SNI) model of neuropathic pain, a most common form of chronic pain. We found that SNI impaired working memory and short-term memory in rats and mice. To explore the potential mechanisms, we studied synaptic transmission/plasticity in hippocampus, a brain region critically involved in memory function. We found that frequency facilitation, a presynaptic form of short-term plasticity, and long-term potentiation at CA3-CA1 synapses were impaired after SNI. Structurally, density of presynaptic boutons in hippocampal CA1 synapses was reduced significantly. At the molecular level, we found that tumor necrosis factor-α (TNF-α) increased in cerebrospinal fluid, in hippocampal tissue and in plasma after SNI. Intracerebroventricular or intrahippocampal injection of recombinant rat TNF mimicked the effects of SNI in naive rats, whereas inhibition of TNF-α or genetic deletion of TNF receptor 1 prevented both memory deficits and synaptic dysfunction induced by SNI. As TNF-α is critical for development of neuropathic pain, we suggested that the over-production of TNF-α following peripheral nerve injury might lead to neuropathic pain and memory deficits, simultaneously.

Figures

Figure 1
Figure 1
SNI impairs spatial working memory and short-term memory (STM), but not spatial reference memory or long-term memory (LTM) in rats. (a) The mechanical allodynia was verified by lasting decrease in paw withdrawal thresholds on ipsilateral side in SNI group, compared with those in sham group (n=15 in SNI group and n=20 in sham group). (b and c) In the same rats working memory and reference memory were evaluated with radial eight-arm maze at 11–20 days after operation. (d–f) In the five rats that did not exhibit significant decrease in paw withdrawal thresholds following SNI, working memory errors but not reference memory errors were also significantly higher, compared with sham group (n=20 in sham group). (g–i) Paw withdrawal thresholds, working memory and reference memory in the rats at 31–40 days after SNI and sham operation are shown (n=10 in each group). (j–l) Paw withdrawal thresholds were tested in SNI and sham groups, and the recognition index for STM and for LTM were determined by novel object recognition test at 19 days and at 20 days after operation. **P<0.01 compared with sham groups (n=8 in each group). Data are presented as means±SEM.
Figure 2
Figure 2
SNI inhibits LTP in CA3–CA1 synapses in a time-dependent manner. (a) SNI did not affect the baseline of fEPSPs and LTP induction by HFS (100 Hz, 50 pulses, four trains with 15 s intervals), which was delivered at 1 h after nerve injury (n=5 in each group). Insert: the raw traces of fEPSPs before (top trace) and after (bottom trace) HFS. (b and c) The time courses of potentiation by HFS in 18–20 h and 6–10 day SNI group (n=6 in each group). (d and e) The recordings were made following behavioral test as illustrated in Figure 1a–c and Figure 1g–i (n=10–15 in each group). (f) The recordings were made in rats (n=5 in SNI group and n=20 in sham group) that did not exhibit allodynia but had working memory deficits, as shown in Figure 1d–f. Data are presented as means±SEM.
Figure 3
Figure 3
SNI reduces presynaptic terminal puncta density and frequency facilitation in CA1 region. (a) The representative images of presynaptic terminal synaptophysin puncta in CA1 from a 20-day-SNI rat and a sham-operated rat are shown. Scale bar=10 μm. (b) The summary data of presynaptic terminal puncta densities in SNI group and sham group (n=8 in each group). (c) The correlation between presynaptic terminal puncta density and the recognition index for short-term memory (r2=0.8746, P=0.0003). (d) Original traces of fEPSPs evoked by 8 Hz stimuli in a SNI rat and a sham-operated rat. (e–g) The facilitation of fEPSPs produced by 2, 4, and 8 Hz stimuli in same SNI rats and in sham rats (n=5 in each group) in 20 min intervals. The test stimulation was 0.066 Hz, and the intensity of conditioning stimuli was identical to that of test stimuli. **P<0.01 compared with sham groups and data are presented as means±SEM.
Figure 4
Figure 4
SNI increases TNF-α in cerebrospinal fluid and hippocampal tissue and the concentration of TNF-α in hippocampus is correlated with LTP inhibition. (a and b) The concentrations of TNF-α in cerebrospinal fluid (CSF) and in hippocampal tissue at different time points following SNI (n=5 at each time point). (c) The correlation analysis between the amplitude of fEPSPs recorded at 30 min after HFS and the concentrations of TNF-α in hippocampal tissue at different time points following SNI (n=5–20 at each time point). **P<0.01 compared with the time point of 0 h after SNI. (d) Representative experiments showed the difference in TNF-α-IR area in CA1 and CA3 between sham operated and SNI rats. (e) The histogram showed the summary data (n=6) of TNF-α-IR-positive staining area in CA1 and CA3 in sham and SNI groups. (f) Identification of specificity of anti-TNF-α used in this study. The TNF-α-IR was clearly decreased in serial sections by preincubating anti-TNF-α antibody with TNF-α. Scale bar=50 μm. *P<0.05, **P<0.01 vs sham groups. Data are presented as means±SEM.
Figure 5
Figure 5
Intracerebroventricular or intrahippocampal injection of rrTNF mimics the effects of SNI. (a and b) Average working memory errors were higher in rats with i.c.v. injection of rrTNF than in aCSF-treated rats, and there was no difference in reference memory performances between the two groups (n=8 in each group). (c–h) The experiments were performed in another cohorts of rats, in which rrTNF (200 ng/ml, 0.5 μl) or aCSF was infused into bilateral hippocampus for 3 successive days (n=8 in each group). (c and d) The recognition index for short-term memory but not that for long-term memory was lower in rrTNF-treated group than that in aCSF-treated group. (e and f) Average working memory errors were higher in rrTNF-treated group than that in aCSF-treated group, but there was no difference in reference memory performances between two groups. (g and h) The concentration of TNF-α in hippocampus but not in CSF was higher in rrTNF-treated group, compared with that in aCSF-treated group (n=4 in each group). **P<0.01 vs aCSF-treated SNI group. Data are presented as means±SEM.
Figure 6
Figure 6
Inhibition of TNF-α synthesis by thalidomide prevents memory deficits and synaptic dysfunction produced by SNI. (a) Paw withdrawal thresholds decreased in DMSO-treated SNI group but not in thalidomide-treated SNI group and sham group (n=8–10 in each group). (b) Average working memory errors in the thalidomide-treated SNI rats were lower than those in DMSO-treated SNI rats, and were not different from those in sham rats. (c) HFS induced LTP in thalidomide-treated SNI rats and sham rats but not in DMSO-treated SNI rats. (d and e) The concentration of TNF-α in three groups of rats as indicated are shown. (f) The recognition index for short-term memory was significantly higher in thalidomide-treated SNI rats than that in DMSO-treated SNI rats. There is no difference between sham rats and thalidomide-treated SNI rats (n=8 in each group). (g and h) The density of presynaptic terminal puncta was higher in thalidomide-treated SNI group than that in DMSO-treated SNI group (n=8 in each group). Scale bar=10 μm. **P<0.01 compared with DMSO-treated SNI group. Data are presented as means±SEM.
Figure 7
Figure 7
Intracerebroventricular injection of TNF-α antibody attenuates memory impairment induced by SNI. (a and b) The recognition index for short-term memory but not that for long-term memory tested at 10 days and at 11 days after SNI was significantly higher in anti-TNF-α-treated group than that in aCSF-treated group (n=7 in each group). (c and d) Average working memory errors but not average reference memory errors accessed after SNI were significantly lower in anti-TNF-α-treated group, compared with aCSF-treated group (n=7 in each group). (e and f) The concentrations of TNF-α in both CSF and in hippocampus were significantly lower in anti-TNF-α-treated rats, compared with aCSF-treated rats (n=4 in each group). **P<0.01 vs aCSF-treated group. Data are presented as means±SEM.
Figure 8
Figure 8
The differential effects of SNI on memory function and hippocampal synapses in wild-type (WT) and TNFR1-knockout mice. (a and b) In WT mice, working memory performance and LTP at CA3–CA1 synapses were impaired in SNI but not in sham-operation group (n=8 in each group). (c–e) The short-term memory index evaluated by NORT and presynaptic synaptophysin puncta density in CA1 are significant lower in SNI WT mice than those in Sham WT mice (n=8 in each group). (f) There was no difference between SNI KO mice and Sham KO mice in working memory performance. (g) The time course of potentiation induced by HFS in SNI KO mice and Sham KO mice, as indicated, at 23–25 days after operation (n=8 in each group). (h) Recognition index for short-term memory in SNI KO and sham KO mice are shown (n=8 in each group). (i and j) The representative images show the presynaptic synaptophysin puncta in CA1 from KO mice after operation and the summary data of presynaptic terminal puncta densities in KO mice. Scale bar=10 μm. **P<0.01 compared with sham group and data are presented as means±SEM.
Figure 9
Figure 9
SNI does not affect the frequency facilitation in TNFR1 knockout mice. (a) The raw traces of fEPSPs evoked by 8 Hz stimuli (1–50 pulses) in SNI and sham-operated TNFR1 KO mice. (b–d) There was no difference in frequency facilitation produced by 2, 4, and 8 Hz stimuli between SNI and sham groups in TNFR1-knockout mice (n=5 in each group). Data are presented as means±SEM.

Similar articles

See all similar articles

Cited by 66 articles

See all "Cited by" articles

Publication types

MeSH terms

Feedback