Short‐Term Effects of Pilocarpine on Rat Hippocampal Neurons in Culture

Abstract

Summary:Purpose: Status epilepticus (SE) has been considered an epileptogenic factor in humans. In the pilocarpine (PILO) model, after a brief period marked by SE, the rats exhibit recurrent spontaneous seizures, mimicking the clinical features of temporal lobe epilepsy. The aim of our study was to identify the molecular actions of PILO that could account for its ability to induce SE.Methods: Whole-cell mode of the patch-clamp technique was applied to cultured hippocampal neurons (2-3 weeks old) in the absence and in the presence of PILO (1-10 M), to study the spontaneous activity, the evoked, and the miniature postsynaptic currents. The postsynaptic currents were isolated pharmacologically.Results: PILO (1 and 10 M) caused an initial increase followed by a decrease in the frequency of spontaneous activity. The increase in the frequency of excitatory postsynaptic currents (EPSCs) and inhibitory PSCs (IPSCs) was blocked by atropine (1 M), indicating that this effect is mediated through muscarinic receptors. PILO also promoted a brief increase of the amplitude of IPSCs indirectly evoked by stimulation of a neuron synaptically connected to the neuron under study. Conversely, PILO promoted a sustained increase on the amplitude of electrically evoked EPSCs. In presence of tetrodotoxin (TTX; 300 nM), PILO (1 M) increased the frequency of miniature EPSCs and IPSCs without changing their amplitude during the first 3 min of application.Conclusions: These results indicate that PILO acting through muscarinic receptor causes an imbalance between excitatory and inhibitory transmission that can result in the generation of SE observed in animals acutely treated with PILO. Key Words: Pilocarpine-Whole cell-Cultured hippocampal neuron-IPSP-EPSP.Status epilepticus (SE) has been considered an epileptogenic factor in humans. Particularly the occurrence of SE or prolonged febrile seizures during childhood, as well trauma or meningitis, has been related to the late appearance of temporal lobe epilepsy (TLE) (1-3). This hypothesis suggests that TLE could be a consequence of initial precipitating injury resulting in a damage of selective hippocampal neuronal groups (4). Neuron loss would be followed by a reorganization of hippocampal excitatory and inhibitory circuitry and mossy fiber sprouting involved in the physiopathology of limbic seizures (2,5).Among the animal models, the pilocarpine (PILO) model (6) has been used to understand the mechanisms that underlie this pathology, because it displays several behavioral, electroencephalographic, and histopathologic similarities to TLE.Cavalheiro et al. (7) demonstrated that the application of pilocarpine, a muscarinic cholinergic agonist, induces a rapid onset of limbic seizures that result in the acute phase, marked by SE, which can last 12 h. After that, the rats have a symptom-free period for 4-44 days called the "silent phase," and then exhibit recurrent spontaneous seizures, the chronic phase. The key to the chronic phase seems to be the occurrence of SE, because those rats without S...

Malnutrition and REM-sleep Deprivation Modulate in Rats the Impairment of Spreading Depression by a Single Sub-convulsing Dose of Pilocarpine

“…3). It has recently been demonstrated that, in presence of 1 to 10 \iM pilocarpine, cultured hippocampal neurones suffer an imbalance between inhibitory and excitatory transmission, which could be involved in the generation of repetitive seizures observed in rats during the acute phase of the pilocarpine model of epilepsy (Priel and Albuquerque, 2002). Unfortunately, no comparable information is available yet, regarding neocortical neurones.…”

Microglia–Neuron Communication in Epilepsy

“…In this model, muscarinic acetylcholine receptor receptor 1 (M 1 ) was shown to be important for development of seizures, since mice lacking this receptor failed to develop seizures following pilocarpine injection (Hamilton et al, ). Downstream of M 1 receptor activation, the homeostatic balance of neuronal excitation–inhibition is tipped toward increased excitability presumably at least in part by increase in glutamate release and sustained NMDA receptor activation (Priel and Albuquerque, ; Smolders et al, ). Although beyond the scope of this review, further details of the mechanics and precise pathological features of these models can be found in several excellent reviews of the kainic acid and pilocarpine models of experimental seizures/epilepsy (Curia et al, ; Levesque and Avoli, ; Levesque et al, ; Turski et al, ).…”

Activation of Group 2 metabotropic glutamate receptors reduces behavioral and electrographic correlates of pilocarpine induced status epilepticus

“…After the initial period of SE, there is a “latent period” during which significant neural reorganization occurs followed by chronic life-long susceptibility to spontaneous, recurrent seizures (Cavalheiro et al, 1996; Curia et al, 2008; Müller et al, 2009; Perez-Mendes et al, 2011; Turski et al, 1989, 1984, 1983). The maintenance and generalization of SE and the development of spontaneous recurrent seizures (SRS) is thought to occur through hyperglutamatergic activity via NMDA receptors in the hippocampus (Nagao et al, 1996; Priel and Albuquerque, 2002; Smolders et al, 1997). Therefore, pilocarpine administration in wild-type mice provides the opportunity to assess novel therapies that interfere with excessive glutamate signaling.…”