Elsevier

Neuroscience

Volume 169, Issue 4, 15 September 2010, Pages 1601-1609
Neuroscience

Cellular and Molecular Neuroscience
Research Paper
Sulforhodamine 101 induces long-term potentiation of intrinsic excitability and synaptic efficacy in hippocampal CA1 pyramidal neurons

https://doi.org/10.1016/j.neuroscience.2010.06.020Get rights and content

Abstract

Sulforhodamine 101 (SR101) has been extensively used for investigation as a specific marker for astroglia in vivo and activity-dependent dye for monitoring regulated exocytosis. Here, we report that SR101 has bioactive effects on neuronal activity. Perfusion of slices with SR101 (1 μM) for 10 min induced long-term potentiation of intrinsic neuronal excitability (LTP-IE) and a long-lasting increase in evoked EPSCs (eEPSCs) in CA1 pyramidal neurons in hippocampal slices. The increase in intrinsic neuronal excitability was a result of negative shifts in the action potential (AP) threshold. The N-methyl d-aspartate receptor (NMDAR) antagonist, AP-5 (50 μM), blocked SR101-induced LTP-IE, but glutamate receptor blockers, AP-5 (50 μM), MCPG (200 μM), and MSOP (100 μM), only partially blocked SR101-induced potentiation of eEPSCs. SR101 induced an enhancement of evoked synaptic NMDAR currents, suggesting that SR101 enhances activation of synaptic NMDARs. SR101-induced LTP-IE and potentiation of synaptic transmission triggered spontaneous neuronal firing in slices and in vivo epileptic seizures. Our results suggest that SR101 is an epileptogenic agent that long-lastingly lowers the AP threshold to increase intrinsic neuronal excitability and enhances the synaptic efficacy to increase synaptic inputs. As such, SR101 can be used as an experimental tool to induce epileptic seizures.

Section snippets

Slice preparation

All experiments were carried out in compliance with the National Institute of Health Guide for the Care and Use of Laboratory Animals and in accordance with guidelines approved by the institute ethics committee for the care and use of animals. Minimal number of rats was used and animal suffering was minimized.

Brain slices were prepared as described previously (Kang et al., 1998). Briefly, 15- to 25-day-old (P15–P25) Sprague–Dawley rats (Charles River Lab., Wilmington, MA, USA) were

SR101 induces LTP-IE

To examine effects of SR101 on neuronal activity, we performed whole-cell current-clamp recording in CA1 pyramidal neurons to measure the action potential (AP) threshold with current–injection steps of 10 pA (Fig. 1A, bottom lines). The AP threshold was defined as the membrane potential at which an AP starts (Fig. 1A, dotted line). Under the control conditions, the AP threshold in pyramidal neurons is in a range of −40 to −52 mV (n=10 neurons). Perfusion of slices with SR101 (1 μM) for 10 min

Discussion

SR101 has recently been identified as a cell type-selective fluorescent marker of astrocytes, both in vivo and in slice preparations. As a result, its use as an experimental tool has rapidly accelerated, based on SR101 as a phenotypic reporter. In the present study, we have found that SR101 is also a potent bioactive compound. In particular, we observed that SR101 induced LTP-IE, increases in synaptic efficacy, and spontaneous firing in hippocampal slices. Strikingly, the concentration of SR101

Acknowledgments

This work was supported in part by grants NS38073 and NS50315 from the US National Institutes of Health and the National Institute of Neurological Disorders Stroke, grant C020925 from the NY State Spinal Cord Injury Research Board and grant 07254001 from US Army Medical Research and Material Command.

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