Role of Nigral Potassium (K

ATP) Channels in Hypoglycemic Seizures

By Ka Lai PoonMentor: Dr. Libor Velíšek

Institution: Albert Einstein College of Medicine

Background Information

Hypoglycemia-induced seizures occur when there is a low level of glucose in the brain. This type of seizures involve deep brain structures, such as the substantia nigra. Repeated hypoglycemic seizures occur in patients with diabetes and may harm their brains.

Substantia Nigra

Two parts: Pars compacta (SNC) - is damaged in Parkinson’s disease.Pars reticulata (SNR) - plays an important role in seizure control.

http://www.foxriverwatch.com/parkinsons_dopamine_pcbs_1intro.html

Substantia Nigra Pars Reticulata

http://cal.vet.upenn.edu/neuro/server/slides/ns_049-SNR.jpg This image represents the SNR, which is the nucleus of the brain where our project is focusing on.

Importance of Study

Since hypoglycemia is generally associated with EEG silencing and seizure occurs when the neurons start firing, then why hypoglycemia seizures occur under conditions of general silencing? How come these specialized neurons are acting the opposite way than the regular neurons? One of the principal glucose-linked regulatory systems is represented by ATP-potassium sensitive channels. And since the SNR contains these specialized channels, therefore we focused our studies on this part of the brain.

ATP-sensitive Potassium (KATP) Channels

One of the many different types of ion channels.

ATP stands for Adenosine Triphosphate, which is an energy-rich substrate that can store and provide energy as needed.

Have the ability to translate the metabolic state into cellular excitability and regulate the firing of glucosensing neurons.

Composed of four regulatory subunits (SUR) and four pore-forming subunits (Kir). Different combinations of these subunits would generate different functions of the KATP channels.

Presented in many major brain areas and have the capability to protect neuronal function during brain ischemia. Therefore, it is very plausible that these channels play a vital role in affecting hypoglycemic seizures.

Objective of Project

Determine the role of the KATP channels in the SNR in hypoglycemic seizures. Both positive and negative effects will be studied by using the KATP channels blocker agent. Infusing the blocker agent could help us keep the channels remain close during the entire experiment since we want to discover what will happen if the channels are closed during the occurrence of hypoglycemic seizures.

Hypotheses

Infusions of the blocker agent (tolbutamide) on non-fasted rats will give us proconvulsant effects and will increase the occurrence of seizures.

Materials and Methods

Adult rats (non-fasted)Stereotaxic brain surgery

Two cannulaes implanted in the SNRanterior

Two-day recovery Microinfusion of the drug in the SNRanteriorSystemic administration of insulinRecording seizures and blood glucose for 4 hoursAt the end, obtain the brains out of the rats for further confirmation of the cannula position

Results

Infusions of the KATP channel blocker agent, tolbutamide, in the SNRanterior have significantly accelerated the onset of seizures as hypothesized.

Results substantiate that the KATP channels in the SNR exert significant effects in hypoglycemic seizures.

Results Cont’d

Weight of the rats. Before we begin the experiment, we recorded down the weight of each rat. The graph shows that the average weight of the control group and experimental group is almost the same, which means that there is no significant difference in their weights.

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Results Cont’d

Mean glucose level of the control group and experimental group before the experiment. It shows that it is almost the same and therefore we can conclude that there is no significant difference between their glucose baselines.

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Results Cont’d

Latency to onset of hypoglycemic seizures. We recorded the time when seizures first occurred to the rats. Infusions of tolbutamide significantly accelerated the onset of hypoglycemic seizures. *Statistical significance was set to P<0.05 (Student’s t-test).

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Tolbutamide

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Discussion and Future Plan

Due to the difficulty of dissolving the drug in a proper way and the insufficient time we have, we are only able to conduct experiments with using tolbutamide, but not the opener agent (diazoxide).

Further investigations are needed to determine the role of the opener agent and the KATP channels have in controlling hypoglycemic seizures.

References

Daunt, J., ATP, The Cardiovascular Cell Physiology Group.

Olanow, C.W. and Tatton, W.G., Etiology and pathogenesis of Parkinson’s disease, Ann Rev Neurosci 1999;22: 123-44.

Seino, S., ATP-Sensitive Potassium Channels: A Model of Heteromultimeric Potassium Channel/Receptor Assemblies, Annu. Rev. Physiol. 1999;61: 337-362.

Acknowledgement

Dr. Libor Velíšek

Dr. Jana Velíšková

Zunju Wu

Hong Wang

Dr. Sat Bhattacharya

Harlem Children Society

Albert Einstein College of Medicine

Memorial Sloan-Kettering Cancer Center