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The heat shock protein 27 kDa (HSP27) is a member of proteins that are highly inducible under various forms of cellular stress. This study describes constitutive HSP27 expression in rat retina and stress-associated expression of HSP27 in an experimental rat glaucoma model. Glaucoma was induced unilaterally using laser photocoagulation of the episcleral and limbal veins. Three and seven days after the elevation of intraocular pressure (IOP), groups of rats were killed. The second laser treatment was performed for those rats killed 14 and 21 days after the first laser treatment. The RGCs were labeled with a retrograde tracer 7 days before kill. The expression of HSP27 was analyzed by Western blotting in retinas of rats killed on day 14 after the first laser treatment. Retinal astrocytes, Müller cells and HSP27-positive cells were visualized using immunohistochemical methods both from retinal whole-mounts and paraffin sections. The total number of retrogradely labeled RGCs decreased by 23.2% after 7 days, 28% after 14 days, and 29.3% after 21 days of elevated IOP when compared with controls. A significant decrease of glial fibrillary acidic protein (GFAP)-immunoreactive retinal astrocytes in laser-treated eyes was observed compared with the controls (accounted for 44.9%, 38.2% and 35% of the control values in the 7-day, 14-day and 21-day groups, respectively). The expression of HSP27 in RGCs and retinal astrocytes was also increased in laser-treated eyes when compared with controls in all groups. However, glycinergic and cholinergic cells in the inner nuclear layer and the highest number of RGCs and astrocytes that expressed HSP27 were found in the 14-day group of rats. The constitutive expression of HSP27 was observed only in retinal astrocytes and Müller cells. This study suggests that constitutive HSP27 expression is a cell-type specific phenomenon in the rat retina. However, at the same time, HSP27 might be considered as a marker for neuronal injury in the rat glaucoma model.

The functional consequences of neuronal loss during epileptogenesis in the lateral and basal amygdaloid nuclei are poorly understood. The present study tested the hypothesis that electrical responsiveness varies in different amygdaloid nuclei in the chronically epileptic amygdala. Further, we examined the amygdaloid region most prone to seizure initiation. Epileptogenesis was triggered in 20 rats by inducing status epilepticus (SE) with electrical stimulation of the lateral nucleus of the amygdala. Electrode-implanted non-stimulated rats served as controls. The occurrence and duration of spontaneous seizures were monitored with video-electroencephalography (EEG) at 8-9 weeks after SE. Thereafter, animals were killed and extracellular recordings were made from slices of both amygdalas. In the lateral nucleus of epileptic animals, the frequency of spontaneous responses was reduced compared with controls (P0.05). The amplitudes of evoked field responses were reduced (P0.01), whereas paired pulse (PP) facilitation was enhanced (Por = 0.05). In the basal nucleus of the epileptic animals, PP facilitation was enhanced (P0.05) and sensitivity to 4-aminopyridine (4-AP)-induced epileptiform activity was increased compared with controls (P0.05). In the epileptic animals, the basal nucleus was also more sensitive than the lateral nucleus to 4-AP-induced epileptiform activity (P0.05). Correlation analysis indicated that longer SE duration was associated with longer half widths (P = 0.001) and smaller slopes (P0.05) of evoked responses as well as with attenuated PP facilitation (P0.01). Moreover, a higher frequency of spontaneous seizures was associated with longer half widths (P0.05) and smaller slopes (P0.05) of evoked responses as well as with enhanced PP facilitation (P0.05). These data suggest that there is a reduced release of glutamate and reduced inhibition in the lateral and basal amygdaloid nuclei in epileptic animals. Further, the basal nucleus is more prone to epileptic activity than the lateral nucleus. Finally, the severity of SE and spontaneous seizures in vivo is associated with electrophysiologic alterations in vitro.

The aim of this study was to characterize the modulation of synaptic transmission in the glutamatergic corticostriatal pathway by cholinergic and adrenergic receptors. In coronal slices of mouse brain, negative-going field potentials were recorded in the dorsal striatum in response to stimulation of the overlying white matter, and their susceptibility to various pharmacological manipulations was studied. The responses were mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors, since they were augmented by aniracetam (0.5-1.5 mM), a positive modulator of AMPA-type glutamate receptors, and blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (> or = 10 microM), a selective antagonist of AMPA receptors. Carbachol (10 microM), a muscarinic agonist, reduced the size of responses and abolished paired-pulse depression; these effects being consistent with previous studies indicating that muscarinic activation inhibits release of glutamate in the corticostriatal pathway. Muscarinic antagonists could block the effect of carbachol. Their rank order was: 10 microM scopolamine (a non-selective muscarinic antagonist) > or = 1 microM 4-diphenylacetoxy-N-methyl-piperidine (M3/M1 antagonist)>1 microM pirenzepine (M1 antagonist)>10 microM methoctramine (M2 antagonist). McN-A-343 (1-10 microM), an M1 muscarinic agonist, was ineffective in this preparation. In contrast, isoproterenol (10-30 microM), a beta-adrenergic agonist, slightly increased the synaptic responses, but it did not affect paired-pulse depression. None of alpha-adrenergic agents (30 nM-1.0 microM dexmedetomidine, an alpha2-adrenergic agonist, 0.3 microM atipamezole, an alpha2-adrenergic antagonist or 30 microM phenylephrine, an alpha1-adrenergic agonist) influenced the size of the responses; neither did these drugs alter paired-pulse depression. These results indicate that the activation of striatal M3-like muscarinic receptors and beta-adrenoceptors, but not M2-like muscarinic receptors and alpha-adrenoceptors, modulates directly corticostriatal glutamatergic neurotransmission.