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Selective Long-term Potentiation in the Pyriform Cortex

其他書名	Role of GABAergic Mechanisms
出版	University of Arkansas, Fayetteville, 1986
URL	http://books.google.com.hk/books?id=g6-HNwAACAAJ&hl=&source=gbs_api

註釋Diazepam (4 mg/kg), which facilitates GABAergic transmission, and bicuculline (0.08 mg/kg), a GABA antagonist, were given intraveneously to two groups of rats implanted with chronic electrodes to examine the role of GABA in potentials evoked in the pyriform cortex by olfactory bulb stimulation, and in the potentiation that appears in this cortex following high-frequency stimulation of the bulb. The evoked potential in the pyriform cortex has two components: period 1, which reflects excitatory input from the olfactory bulb and feedforward excitation within the pyriform cortex, and period 2, which is temporally associated with and may partially reflect GABA-mediated inhibition in the pyriform cortex. In naive animals, diazepam significantly increased period 2 duration without affecting input from the olfactory bulb. Bicuculline produced a brief and much smaller increase in period 2 duration. Following tests in naive animals, half of the rats from each drug group received repeated high-frequency stimulation of the olfactory bulb while the remaining rats served as low-frequency controls. High-frequency stimulation produced potentiation (i.e., an increase in duration) of period 2 that lasted at least 3 days; no changes were seen in period 1, which primarily reflects input from the olfactory bulb. Changes in control animals were negligible. Following potentiation, the effects of diazepam and bicuculline on the expression of potentiation were examined. As in naive animals, diazepam increased period 2 duration during these tests. Bicuculline had no effects on the expression of potentiation even though a near convulsant dose was used. This suggests that with systemic bicuculline administration it is difficult to antagonize GABA sufficiently to alter evoked potentials in the pyriform cortex without producing convulsions. The primary finding of this experiment was that diazepam mimicked accurately the effects of potentiation on the pyriform cortex evoked potential. The absence of a consistent effect by bicuculline appeared to be due to difficulties inherent in its systemic administration. Based on these and previous findings, a model is proposed wherein period 2 in non-potentiated rats is mediated by conductance changes not associated with GABAergic synapses while the potentiated portion of period 2 is mediated by GABAergic synapses.