Elsevier

Neuroscience

Volume 149, Issue 2, 26 October 2007, Pages 382-391
Neuroscience

Molecular neuroscience
Modification of purinergic signaling in the hippocampus of streptozotocin-induced diabetic rats

https://doi.org/10.1016/j.neuroscience.2007.08.005Get rights and content

Abstract

Diabetic encephalopathy is a recognized complication of untreated diabetes resulting in a progressive cognitive impairment accompanied by modification of hippocampal function. The purinergic system is a promising novel target to control diabetic encephalopathy since it might simultaneously control hippocampal synaptic plasticity and glucose handling. We now tested whether streptozotocin-induced diabetes led to a modification of extracellular ATP homeostasis and density of membrane ATP (P2) receptors in the hippocampus, a brain structure involved in learning and memory. The extracellular levels of ATP, evaluated in the cerebrospinal fluid, were reduced by 60.4±17.0% in diabetic rats. Likewise, the evoked release of ATP as well as its extracellular catabolism was also decreased in hippocampal nerve terminals of diabetic rats by 52.8±10.9% and 38.7±6.5%, respectively. Western blot analysis showed that the density of several P2 receptors (P2X3,5,7 and P2Y2,6,11) was decreased in hippocampal nerve terminals. This indicates that the synaptic ATP signaling is globally depressed in diabetic rats, which may contribute for diabetes-associated decrease of synaptic plasticity. In contrast, the density of P2 receptors (P2X1,2,5,6,7 and P2Y6 but not P2Y2) increased in whole hippocampal membranes, suggesting an adaptation of non-synaptic P2 receptors to sense decreased levels of extracellular ATP in diabetic rats, which might be aimed at preserving the non-synaptic purinergic signaling.

Section snippets

Reagents

The antibodies against P2X1 (generated against residues 382–399 of rat P2X1 and used at a 1:500 dilution from a 0.6 mg/ml stock), P2X3 (generated against residues 383–397 of rat P2X3 and used at a 1:1000 dilution from a 0.2 mg/ml stock), P2X4 (generated against residues 370–388 of rat P2X4 and used at a 1:500 dilution from a 0.3 mg/ml stock), P2X7 (generated against residues 576–595 of rat P2X7 and used at a 1:5000 dilution from a 0.3 mg/ml stock), P2Y2 (generated against residues 227–244 of

Modification of extracellular ATP concentration and metabolism

We first evaluated if the diabetic rats presented abnormal extracellular ATP levels in the brain. As shown in Fig. 1A, 1 month after STZ-induction of diabetes, the concentration of ATP in the CSF was less than half of that in control rats. The synaptic levels of ATP were also decreased in diabetic rats, as gauged by the reduction of the K+-induced evoked release of ATP from hippocampal nerve terminals (Fig. 1B, C).

We next investigated the rate of extracellular catabolism of ATP by following the

Discussion

The main conclusion of this study is that there is a deregulation of P2 receptor-mediated signaling in the hippocampus of STZ-induced type 1 diabetic rats. We found that there was a decrease in the CSF levels of ATP in diabetic rats, together with a decrease of the evoked release of ATP in hippocampal nerve terminals, suggesting that P2Rs may be facing lower concentration of extracellular ATP. Also the extracellular metabolism of ATP is reduced in nerve terminals from the diabetic hippocampus,

Conclusion

In conclusion, the present study provides evidence showing that the ATP signaling system is compromised in the hippocampus of STZ-treated rats, an experimental model of type 1 diabetes mellitus. These modifications could lead to alterations in the modulation of neurotransmission and gliotransmission, which may contribute to the diabetes-induced progressive cognitive impairment, although the direct impact of such alterations on both neuronal and glial functions remains to be determined. In

Acknowledgments

This work was supported by Fundação para a Ciência e a Tecnologia (FCT, grant POCTI/SAU-NEU/56098/2004) and by Fundo Fundação Oriente/Johnson & Johnson Para a Saúde. João M. N. Duarte acknowledges a PhD grant from FCT (SFRH/BD/17795/2004). Jean Pierre Oses acknowledges a PhD grant from CNPq/Brasil (200127/2005-5).

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