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In the previous study we showed that exogenous CRF (1 μg/rat, icv) enhanced rat-freezing responses and increased expression of CRFrelated immunoreactive complexes in the amygdala. On the other hand, a non-selective CRF receptor antagonist, α-helical CRF(9-41) (10 μg/rat, i.c.v.) decreased rat fear response and increased the concentration of GABA in the amygdala (in vitro). The aim of the present study was to examine the effects of CRF and α-helical CRF(9-41), on the freezing reaction in the conditioned fear test and the release of amino acids in the central nucleus of amygdala (CeA), using microdialysis technique. It was found that CRF increased the concentration of aspartate, glutamate and Glu/GABA ratio in the CeA, an effect that preceded an increased expression of anxiety-like responses, which appeared 15 min after drug administration. α-helical CRF(9-41), decreased rat freezing responses and increased the local concentration of GABA, during the fi rst 30 min of observation. The present data show an important role of CRF in the central nucleus of the amygdala in the integration of anxiety-related, biochemical and behavioural responses, and suggest an involvement of amino acids innervation of the CeA, in the effects of this neurohormone.
Rats were given 14 “daily” (6 doses/week) s.c. doses of 0.9% NaCl (Sal), morphine (Mor), or methadone (Met), then left untreated for 14 days, and fi nally challenged with Mor, except that half each of the Sal groups were given Sal instead. All the rats were then tested for open fi eld behavior, and were sacrifi ced 2 h post-challenge. Striatal (CPu), accumbal (Acb), sensorimotor cortex (S1) and prefrontal cortex contents of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 3-methoxytyramine (3 MT, assessed only in the CPu and Acb) were measured by HPLC. Analysis of total distance covered by the rats showed Mor and Met-induced sensitization to Mor in the WHP rats only, whereas the distance covered in the central part of the test arena was signifi cantly affected (increased) only by the Mor pretreatment and only in the WHP rats. There was no signifi cant between-line or treatment-related difference in DA content, and no signifi cant between-line difference in baseline DA metabolite contents, except that S1 HVA content was signifi cantly higher in drug-naive WLP rats than in drug-naive WHP rats. HVA and – to a lesser extent – DOPAC contents were, in general, higher in the Mor-challenged rats than in the respective Sal-treated controls, but the differences were more pronounced in the WLP rats than in their WHP counterparts, whereas the opioid -pretreated WHP rats showed higher CPu and Acb 3 MT contents than their WLP counterparts.
In the present study, the c-Fos expression was used to map brain structures recruited during the evolution of seizures after repeated, administration of pentylenetetrazol at the subconvlusive dose (35 mg/kg, i.p.), in rats. It has been found that the earliest expression of cFos, at the stage 1,2 of kindling, appeared in the nucleus accumbensshell, the piriform cortex, the prefrontal cortex and striatum. On the 3rd stage of kindling, the central amygdala nucleus, the entorhinal cortex, and the lateral septal nucleus (LSV), showed an enhanced expression of c-Fos. On the 4th stage of kindling, c-Fos was increased in the basolateral amygdala, and CA1 area of the hippocampus. Finally, c-Fos labelling was enhanced in the dentate gyrus of the hippocampus, only when the stage 5 of kindling, i.e. the clonic-tonic convulsions, appeared. The most potent changes in c-Fos (in a descending order) were shown in the dentate gyrus, piriform cortex, CA1 area, the LSV, basolateral amygdala, central amygdala nuclei, and prefrontal cortex. It appeared, that there are important similarities in the structures recruited at the beginning and at the end of electrically and chemically-induced kindling, i.e. the piriform cortex and the hippocampal dentate gyrus, respectively. On the other hand, the differences gradually disappear at the later stages of kindling, followed by the symmetrical propagation of epileptic activity from the limbic system to the neocortex, during the generalized seizures.
In the present study the effects of a protein synthesis inhibitor, cycloheximide (125 μg, i.c.v.), on the expression and reconsolidation of pentylenetetrazol-induced kindled seizures, were studied in rats. Cycloheximide given repeatedly (every second day) to fully kindled rats, immediately after 4 consecutive sessions of PTZ-seizures, did not modify the strength of subsequent fi ts of convulsions. On the other hand, the protein synthesis inhibitor signifi cantly attenuated the strength of convulsions when the drug was administered 1 h before the PTZ injection, every second day for 5 consecutive experimental sessions. However, when cycloheximide was omitted in a consecutive session, PTZ induced a fully developed fi t of tonicclonic convulsions, indicating that cycloheximide-induced changes in seizure intensity were transitory, not related to a stable modifi cation in the function of neuronal circuits responsible for kindling seizures. The present fi ndings suggest that the mechanisms underlying epileptogenesis are very resistant to modifi cation, and as such, are not the subject to permanent changes even under the infl uence of protein synthesis inhibition. One possible reason may be the depth and multiplicity of changes induced by seizures (i.e. alterations in enzymes, receptors, structural proteins, growth factors, etc.), that may cause permanent biochemical and morphological alterations in the brain that give rise to the kindled seizures.
In recent years we have elaborated an animal model to examine the neurochemical background of differences in the individual responses to conditioned aversive stimuli, using the strength of a rat contextual fear test, as a discriminating variable: low responders (LR), i.e. rats with duration of a freezing response one standard error, or more, below the mean value and high responders (HR), i.e. rats with duration of a freezing response one standard error, or more, above the mean value. It was found that 1.5 h after a testing session of contextual fear test, the LR animals showed a higher density of 5-HT1A and glucocorticoid immunoreactivity-expressing cells (GRsir) in the cortical M2 area and hippocampal dentate gyrus as well as an increased number co-expressing 5-HT1A /GRs-ir in the same areas. The HR rats had a signifi cantly higher concentration of 5-HT1A and GRs-ir in the basolateral amygdala. The present data add more arguments for the neurobiological background of differences in individual responses to aversive conditioned stimuli.
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