ABSTRACT
Objective: Low-frequency stimulation [LFS] exerts suppressive effects in kindled animals. It is believed that overstimulated glutamatergic and decreased GABAergic transmission have long been associated with seizure activity. In this study, we investigated the effect of electrical LFS on different parameters of spontaneous excitatory and inhibitory post-synaptic currents [sEPSCs and sIPSCs] in hippocampal CA1 pyramidal cells in kindled animals
Materials and Methods: In this experimental study, rats were kindled by electrical stimulation of the hippocampal CA1 area in a semi-rapid manner [12 stimulations/day]. The animals were considered fully kindled when they showed stage 5 seizures on three consecutive days. One group of animals received LFS 4 times at 30 seconds, 6 hours, 18 and 24 hours following the last kindling stimulation. Each LFS consisted of 4 packages at 5 minutes intervals. Each package of LFS consisted of 200 pulses at 1 Hz and each monophasic square wave pulse duration was 0.1 millisecond. At 2-3 hours post-LFS, acute hippocampal slices were prepared and a whole cell patch clamp recording was performed in all animals to measure the different parameters of sEPSCs and sIPSCs
Results: In kindled animals, the inter-event interval [as an index of occurrence] of sEPSCs decreased, whereas sIPSC increased. In addition, the decay time constant of sIPSCs as an index of the duration of its activity decreased compared to the control group. There was no significant difference in other parameters between the kindled and control groups. Application of LFS in kindled animals prevented the observed changes. There was no significant difference between the measured parameters in kindled+LFS and control groups
Conclusion: LFS application may prevent seizure-induced increase in the occurrence of sEPSCs and seizure-induced decrease in occurrence and activity duration of sIPSCs
Subject(s)
Animals, Laboratory , Male , CA1 Region, Hippocampal , Pyramidal Cells , Inhibitory Postsynaptic Potentials , Excitatory Postsynaptic Potentials , Seizures/therapy , Rats, WistarABSTRACT
The rostral ventromedial medulla [RVM] acts a key role in the descending inhibitory pain modulation. Neuropeptide orexin-A [ORXA] is confined to thousands of neurons in the lateral hypothalamus [LH]. While RVM gets the orexinergic projections, the orexin receptors are also expressed in this structure. The aim of this study was to specify the cellular effects of ORXA on RVM neurons in vitro by using the whole cell patch-clamp recording. RVM neurons were classified into three types based on their electrophysiological characteristics. Type 1 neurons exhibited an irregular spontaneous activity which was interrupted by periods of pause in 25% of recorded neurons. Type 2 neurons did not show any spontaneous baseline activity [53.8% of recorded neurons]. Type 3 neurons fired repetitively without interruption [51.2% of recorded neurons]. ORXA had either inhibitory or excitatory effects on 53.8% [7/13] of type 1 neurons. ORXA excited 46.4% [13/28] of type 2 neurons and 27.3% [3/11] of type 3 neurons. The excitatory effect of ORXA observed in type 2 neurons was suppressed by an orexin 1 receptor [OXR1] antagonist, SB-334867. Briefly, we hypothesized that the ORXA mediated excitation and/or inhibition in RVM neurons might work as a mechanism to modulate pain processing by orexinergic neurons
ABSTRACT
Adenosine has been considered as a fine-tuner of the neurotransmitters in the nerve system. Adaptive changes in the brain adenosine system occur in some patho-physiological situations such as chronic exposure to morphine. In this study, the adaptive changes in the adenosine deaminase activity as a key enzyme in the adenosine metabolism that converts adenosine to inosine and ammonia, irreversibly, due to morphine dependence and tolerance to anti-nociceptive effects of sodium-salicylate were investigated. Morphine dependence was induced by morphine administration in tap water [0.4mg/ml for 24 days]. Tolerance to sodium-salicylate was induced by 6 i.p. injection [1 injection/day] of sodium-salicylate. Tolerance to antinociceptive effects of sodium-salicylate was measured by tail flick [TF] and hot plate [HP] tests. Right hippocampus was dissected, homogenized at phosphate buffer, centrifuged and then the supernatant fraction was isolated. Protein content of the samples was measured by the Bradford method. Hippocampus adenosine deaminase activity was measured by a calorimetric method of enzyme assay which is based on the direct measurement of the produced ammonia from excessive adenosine degradation by adenosine deaminase. Daily injection of Sodium-salicylate produced antinociception in early days by latency increase rather than saline injection [P<0.0001] but in the following days this antinociceptive effect progressively decreased so at the day 5 and 6 following injection it was similar to saline [P>0.05]. Injection of morphine [5mg/Kg] at the day 7 showed more increase in the latency of saline injected rather than sadium-salicylate injected [P<0.001]. Adenosine deaminase activity was significantly higher in sucrose administrated rather than chronic morhine administrated [P<0.05] and in saline injected rather than sodium-salicylate injected [P<0.05]. Single injection of sodium-salicylate and its control shows the same activity. There was no significant difference in enzyme activity of morphine dependent with sadium-salicylate tolerance [P>0.05]. This decline in the adenosine deaminase activity may be related with adaptation in brain adenosine system subsequent of dependent to morphine or tolerance to sodium-salicylate
ABSTRACT
Adenosine has many of the characteristics of a regulator of cerebral blood flow and adenosine receptors change in morphine dependency. In this study the changes in adenosine receptors' responsiveness of pial vessels in the hind limb area of the sensory cortex were evaluated in morphine dependent rats [MDR] using the laser Doppler flowmetry technique. Adult male Sprague Dawley rats [250-350 g] were used in all experiments. Animals were made morphine dependent, thereafter local effects of adenosine receptor agonists and antagonists on regional cerebral blood flow [rCBF] were investigated. Results obtained in this study show that adenosine [10[-5], 10[-4], 10[-3]M] increases rCBF in a dose dependent manner in sham operated, control and MDR, so that the increase of rCBF in MDR is statistically significant [p<0.01]. This response was inhibited by theophylline [5x 10[-5]M]. Lidocaine [2%] reduced adenosine-induced increase in rCBF of MDR. N6-cyclohexyladenosine [10[-6], 10[-5], 10[-4] M] and 8-cyclopentyltheophylline [10[-6]M] as a selective agonist and antagonist of adenosine Al receptors had no significant effect on rCBF in control and MDR. CGS-21680 [10-6 M] as a selective adenosine A2a receptor agonist, increased rCBF in MDR significantly [p<0.05]. This response was antagonized by ZM-241385. NECA [10[-6]M] as a adenosine A2b receptor agonist, increased rCBF in MDR significantly [p<0.05]. This response was antagonized by Alloxazine. The results of this study indicate an increase in adenosine A2 receptors' [including A2a and A2b subtypes] responsiveness in hind limb sensory cortex of MDR