Unitary “bursting” activity: A definition

5443 CORTICOSTEROIDS REDUCE ECTOPIC NEURAL DISCHARGE ORIGINATING IN EXPERIMENTAL NERVE-END NEUROMAS. M. Devor, R. GovrinLife Sciences Institute, Hebrew Lippmann*, and P. Raber* University of Jerusalem, Jerusalem 91904, ISRAEL Corticosteroids are often hiahly effective in Aim of Investigation: relievina itch and pain associated with a number of dermatological, rheumatic The general presumotion is that the drugs act by reduand other conditions. cing inflammation, and only secondarily affect nerve fibers by chanqing the The aim of this study was to investlevel of some irritant(s) in the tissue. iqate the effect of corticosteroids on primary nerve fiber hyperexcitability in which inflammation does not feature prominently. Experimental neuromas were made in adult male rats by ligatina Methods: At the time of the nerve injury, or l-10 days and cutting the sciatic nerve. later, we either injected commercially available preparations of triamcinolone hexacetonide (Lederspan), triamcinolone diacetate (Ledercort), or dexamethasone (Dexacort) into the nerve end, or applied the drugs to the perineurial surface Quantitative measurements were made about 10 mm. proximal to the ligature. of the amount of spontaneous discharae originatinq in the neuroma, and its sensitivity to mechanical stimulation. All corticosteroid treatments siqnificantly reduced the Percent Results: of neuroma fibers with spontaneous discharqe compared to equivalent treatment Intraneural injection was somewith saline (mean reduction was 72.6% n=28). In addition, there was a what more effective than superficial treatment. dramatic reduction in the sensitivity of the neuromas to mechanical stimulation. Electrophysiological and moroholoaical data indicated that there was no Systemic administration of equidirect nerve degeneration due to the drugs. valent corticosteroid doses was without effect on neuroma activity. Corticosteroids dramatically reduced the hyperexcitability Conclusions: The site of action would aopear to be the damaqed of experimental neuromas. axons and axon sprouts themselves. UNITARY "BURSTING" ACTIVITY: A DEFINITION. U~s~~tZ"~Zi~~~ m1 A.V. Apkarian*, Department of Neurosurgery, Center, State University of New York, Syracuse, New York 13210, USA. Central to the assumed cause of some pain states is the idea that sensory neurons, after denervation or damage may exhibit "bursting" firing Such neuronal firing patterns are usually qualitatively characpatterns. terized as spontaneous, periodic, high frequency groups of action potenSuch a definition makes the identification of bursting cells tials. subjective and precludes the ability to statistically compare populations of cells in terms of the presence or absence of "bursting" activity. The purpose of this study is to present a statistical definition to test for The definithe presence of bursting activity in neuronal spike trains. tion is based on interspike intervals and the assumption that the spike events used represent a stationary point process. The episodic nature of the groups of spikes dictates that, first, the interspike interval histogram (ISIH) must be multimodal. Secondly, since periodic high frequency activity indicates time ordering of the probability of spike occurence, there must be a significant difference between the autoconvolution (which is based on the order independent probability of firing and is calculated from the ISIH) and the autocorrelation (which is the actual probability of firing derived from the time ordered data). The difference between the two distributions must be significant and indicate that there are a greater number of short interspike intervals in the real data (autocorrelation) when compared to the theoretical order independent distribution (autoconvolution). Single unit data from cat dorsal horn has been used to compare this definition of bursting with other measures of activity including mean frequency and arbitrarily defined clumping of high frequency spikes. These comparisons support the usefulness of our definition.