Long Term Alteration of Intracellular Calcium Homeostatic Mechanisms in Acutely Isolated Hippocampal Pyramidal Neurons from Pilocarpine-Induced Epileptic Rats.
Abstract number :
1.058
Submission category :
Year :
2000
Submission ID :
1430
Source :
www.aesnet.org
Presentation date :
12/2/2000 12:00:00 AM
Published date :
Dec 1, 2000, 06:00 AM
Authors :
Mohsin Raza, Shubro Pal, Azhar Rafiq, Robert J Delorenzo, Virginia Commonwealth Univ, Richmond, VA; Virginia Comonwealth Univ, Richmond, VA.
RATIONALE: Studies in neuronal culture models of recurrent epileptiform discharges have shown impaired ability of neurons to restore resting [Ca++]i levels following exposure to glutamate (glu). In this report, we determined (1) resting intracellular calcium ([Ca++]i) and (2) [Ca++]i response to glu in acutely isolated hippocampal pyramidal neurons from epileptic and control rats. METHODS: Hippocampal pyramidal neurons were isolated from hippocampi of one year old epileptic rats and their age-matched controls by a modified method as described by Kay and Wong, 1986. The animals were made chronically epileptic by treatment with pilopcarpine (Rice et al., 1998). Resting [Ca++]i and changes in [Ca++]i in response to glu were measured by flouorescent microscopy using both high affinity Fura-2 and low affinity Fura-ff ratioable dyes to more accurately evaluate [Ca++]i levels at both high and low Ca++ concentrations. RESULTS: In neurons (n=161) isolated from chronically epileptic animals, the resting [Ca++]i was 393.6 b 25.2 nM in comparison to 207.1 19.3 nM in neurons (n=174) isolated from age-matched controls (p < 0.002). In control neurons exposed to 5, 10 and 50 M glu, [Ca++]i returned to the pre-exposure values within 15 to 35 min, while in neurons isolated from epileptic animals the [Ca++]i took significantly longer to return to baseline values. Using the lower affinity flourescent dye, Fura-ff, both control and epileptic neurons reached the same maximal levels of [Ca++]i in response to glu, but [Ca++]i levels took longer to return to base line levels in the epileptic neurons. In wash with low Ca++ extracellular solutions, [Ca++]i returned to baseline values in both groups. [Ca++]i alterations persists for as long as 1 year in the epileptic animals. CONCLUSIONS: The results suggest that alterations in neuronal [Ca++]i homeostatic mechanisms are associated with epileptic neurons for as long as 1 year following epileptogenesis. This alteration in Ca++ homeostatic mechanisms may play a role in some of the long lasting neuroplasticity changes associated with epilepsy.