Understanding the pathophysiogenesis of temporal lobe epilepsy (TLE) largely rests on the use of models of status epilepticus (SE), as in the case of the pilocarpine model. The main features of TLE are: (i) epileptic foci in the limbic system; (ii) an “initial precipitating injury”; (iii) the so-called “latent period”; and (iv) the presence of hippocampal sclerosis leading to reorganization of neuronal networks. Many of these characteristics can be reproduced in rodents by systemic injection of pilocarpine; in this animal model, SE is followed by a latent period and later by the appearance of spontaneous recurrent seizures (SRSs). These processes are, however, influenced by experimental conditions such as rodent species, strain, gender, age, doses and routes of pilocarpine administration, as well as combinations with other drugs administered before and/or after SE. In the attempt to limit these sources of variability, we evaluated the methodological procedures used by several investigators in the pilocarpine model; in particular, we have focused on the behavioural, electrophysiological and histopathological findings obtained with different protocols. We addressed the various experimental approaches published to date, by comparing mortality rates, onset of SRSs, neuronal damage, and network reorganization. Based on the evidence reviewed here, we propose that the pilocarpine model can be a valuable tool to investigate the mechanisms involved in TLE, and even more so when standardized to reduce mortality at the time of pilocarpine injection, differences in latent period duration, variability in the lesion extent, and SRS frequency.

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Proton receptors of the acid-sensing ion channel (ASIC) family are expressed in sensory neurons and thus could play a critical role in the detection of noxious acidosis. To investigate the subunit composition of native ASICs in peripheral and central neurons, we coinjected human as well as rodent ASIC2a and ASIC3 subunits in Xenopus oocytes. The amplitudes of acidinduced biphasic responses mediated by co-expressed ASIC2a and ASIC3 subunits were much larger (as much as 20-fold) than the currents mediated by the respective homomers, clearly indicating functional association. The reversal potential of the ASIC2a؉3 current (>؉20 mV) reflected a cationic current mainly selective for sodium. The sensitivity to pH or amiloride of single versus co-expressed ASIC subunits was not significantly different; however, gadolinium ions inhibited ASIC3 and ASIC2a؉3 responses with much higher potency (IC 50 ϳ40 M) than the ASIC2a response (IC 50 >1 mM). Biochemical interaction between ASIC2a and ASIC3 subunits was demonstrated by co-purification from transfected human embryonic kidney (HEK293) cells and Xenopus oocytes. Our in situ hybridization data showed that rat ASIC2a and ASIC3 transcripts are colocalized centrally, whereas reverse transcription-polymerase chain reaction data led us to detect co-expression of human ASIC2a and ASIC3 subunits in trigeminal sensory ganglia, brain, and testis where they might coassemble into a novel subtype of proton-gated channels sensitive to gadolinium.

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In limbic seizures, neuronal excitation is conveyed from the entorhinal cortex directly to CA1 and subicular regions. This phenomenon is associated with a reduced ability of CA3 to respond to entorhinal cortex inputs. Here, we describe a lesion that destroys the perforant path in CA3 after status epilepticus (SE) induced by pilocarpine injection in 8-week-old rats. Using magnetic resonance imaging, immunohistochemical, and ultrastructural analyses, we determined that this lesion develops after 30 minutes of SE and is characterized by microhemorrhages and ischemia. After a longer period of SE, the lesion invariably involves the upper blade of the dentate gyrus. Adult rats treated with subcutaneous diazepam (20 mg kg for 3 days) did not develop the dentate gyrus lesion and had less frequent spontaneous recurrent seizures (p < 0.01). Young (3-week-old) rats rarely (20%) developed the CA3 lesion, and their spontaneous seizures were delayed (p < 0.01). To investigate the role of the damaged CA3 in seizure activity, we reinduced SE in adult and young epileptic rats. Using FosB/DeltaFosB markers, we found induction of FosB/DeltaFosB immunopositivity in CA3 neurons of young but not in adult rats. These experiments indicate that SE can produce a focal lesion in the perforant path that may affect the roles of the hippocampus in epileptic rats.

The aim of the present experiment was to study the effects of early postnatal maternal separation on behavioural and adrenocortical responses to novelty in rats tested as adults. Sprague-Dawley rat pups were exposed to daily maternal separation (5 h/day) from postnatal day 2 to 6, during the stress hyporesponsive period. Since this procedure requires physical contact with the animals, a first control group of daily handled pups was introduced. A second control group, consisting of pups never handled or separated from the mother, was also considered. At postnatal day 45, the rats were tested in a two-compartment exploratory apparatus: the maternally separated and the non-handled rats, whose behavioural performance did not differ, showed higher emotional behaviour when compared with the handled rats (P < 0.05), suggesting that the handling procedure but not maternal separation improved the capacity to cope with novelty. Corticosterone plasma levels were found to be higher in the maternally separated rats than in the other two groups (P < 0.05), either at resting conditions or at 30 min after novelty exposure (P < 0.05). Levels of nuclear glucocorticoid receptor immunoreactivity in the CA1 hippocampal field were shown to be regulated by novelty exposure, as expected, in both the handled and the non-handled rats but not in the maternally separated rats. In conclusion, repeated maternal separation periods of 5 h/day during the first week of life produced long-lasting effects on the hippocampal regulation of the hypothalamic-pituitary-adrenocortical axis, which appear to be associated with increased responsiveness to stress stimuli in adulthood.

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