Research reportCysteamine pre-treatment reduces pentylenetetrazol-induced plasticity and epileptiform discharge in the CA1 region of rat hippocampal slices
Introduction
The hippocampus is directly involved in the development of epilepsy and other types of adaptive behavior such as learning and memory [16], [31]. It has been reported that some subregions of the hippocampus are more likely to initiate epileptiform activity than others. In the hippocampus, the site of origin of ictal-like activity appears to be located in area cornus ammonis 1 (CA1), while interictal-like activity has been found in the CA2–CA3 region [9].
Pentylenetetrazol (PTZ) is one of the most extensively used epileptogenic agents. It induces absence-type seizures (with a dose of ∼25 mg/kg) or convulsions (with ≥50 mg/kg) [23]. However, its mechanism of action has not yet been completely determined. Experimental data have indicated that PTZ blocks GABAergic mechanism [24].
Exposure to PTZ in hippocampal slices results in the appearance of spontaneous interictal-like discharges and alteration of orthodromically induced field potentials of repetitive burst discharges [12]. Bingmann and Speckmann described prolonged seizure-like events after repeated application of high concentrations of PTZ [3]. However, such events were not seen in other experiments [12]. We have shown that a transient PTZ application produces a long-lasting increase in population spike amplitude [18].
Somatostatin, a neuropeptide, is widely distributed throughout the brain including the hippocampal formation [6], [8], [27]. The hippocampal CA1 area, in particular, has an unusually rich collection of somatostatinergic neurons and fibers [4]. Microiontophoretic application of somatostatin elicits excitatory responses in neocortical, hippocampal and striatal neurons in vivo [17] as well as in hippocampal slices [6]. It has been shown that levels of immunoreactive somatostatin are increased in certain brain regions of rat kindled by focal amygdala stimulation [7]. Also somatostatin augments the spread of limbic seizures from hippocampus [21]. The absence of a specific somatostatin receptor antagonist is an important limitation to the study of this peptides’ functional role in the brain [27]. However, cysteamine, an agent which causes depletion of brain and gastrointestinal immunoreactive somatostatin [14], [19], [25], is a useful tool for the blockade of the actions of the peptide in the central nervous system. Cysteamine suppresses the development of long-term potentiation in the mossy fiber-CA3 pathway [15] and potentiates dentate granule cell responsiveness to perforant path activation [30]. In PTZ-kindled rats, systemic cysteamine causes a significant and long-lasting decrease in the severity of convulsive responses to PTZ [1]. It also acts to prevent attainment of the kindled state when applied before or during the kindling paradigm [2]. These findings suggest that brain endogenous somatostatin may play a role in seizure susceptibility and synaptic plasticity. Therefore, the current experiments were designed to determine whether a prior treatment with cysteamine would prevent PTZ-induced potentiation and epileptiform activity in hippocampal CA1.
Section snippets
Animals
The subjects were male albino rats weighting 100–160 g. They were housed five per cage and kept in the animal care facility under controlled temperature and lighting (lights on: 8 a.m.–8 p.m.) with food and water freely available.
Slice preparation
Under ether anesthesia, rats were decapitated and their right hippocampus was rapidly dissected. Transverse slices (450 μm) were prepared by a standard method [13] and then placed in a prechamber containing an aerated artificial cerebrospinal fluid (ACSF) which
Baseline CA1 synaptic response
Electrical stimulation of the afferent fibers in the stratum radiatum elicited a synchronous response from the CA1 pyramidal cells which could be measured extracellularly. There was no frequency potentiation at the test stimulation rate of 0.1 Hz. Fig. 1A presents mean size of baseline PSA over all stimulus intensities for the two groups. The difference between two groups was generally significant (F1, 132=8.07, P=0.005). Post hoc analysis indicated that this difference was concentrated at
Discussion
Activity dependent changes in synaptic efficacy are critical for the development of appropriate neural circuits and for many forms of neural plasticity [10]. These changes in synaptic activity can elicit persistent neural responses which are critical mechanisms for lasting changes in brain function. We have reported that a transient PTZ application causes a long-lasting potentiation of population spike amplitude in hippocampal CA1 [18]. The current experiments were designed to determine whether
References (31)
- et al.
Pentylenetetrazol-induced kindling is prevented by prior treatment with cysteamine
Eur. J. Pharmacol.
(1990) - et al.
Profound suppression of kindled seizures by cysteamine: possible role of somatostatin in kindled seizures
Brain Res.
(1983) - et al.
Removal of extracellular calcium after conditioning stimulation disrupts long-term potentiation in the CA1 region of rat hippocampal slices
Neuroscience
(1997) - et al.
Long-term potentiation as a function of test pulse intensity: a study using input/output profiles
Brain Res.
(1994) - et al.
Effects of pentetrazol on neuronal activity and on extracellular calcium concentration in rat hippocampal slices
Epilepsy Res.
(1990) - et al.
A facilitatory role of endogenous somatostatin in long-term potentiation of the mossy fiber-CA3 system in guinea-pig hippocampus
Neurosci. Lett.
(1991) - et al.
Low frequency perforant path stimulation as a conditioned stimulus demonstrates correlations between long-term synaptic potentiation and learning
Physiol. Behav.
(1986) - et al.
Central actions of somatostatin
Eur. J. Pharmacol.
(1980) - et al.
Primed-burst potentiation occludes the potentiation phenomenon and enhances the epileptiform activity induced by transient pentylenetetrazol in the CA1 region of rat hippocampal slices
Brain Res.
(2000) - et al.
Selective depletion of somatostatin in rat brain by cysteamine
Brain Res.
(1982)
Cysteamine normalizes cerebral somatostatin level and binding in pentylenetetrazol-kindled rats
Life Sci.
Somatostatin-like immunoreactivity (SLI) in cisternal cerebrospinal fluid of rats kindled by pentylenetetrazol
Brain Res.
Interaction of pentylenetetrazol and tetrazol analogues with the picrotoxin in site of the benzodiazepine-GABA receptor ionophore complex
Eur. J. Pharmacol.
Brain somatostatin: receptor-coupled transducing mechanisms and role in cognitive functions
Pharmacol. Res.
Acceleration of aging-related gliopathic changes and hippocampal dysfunction following intracerebroventricular infusion of cysteamine in adults rats
Neuroscience
Cited by (12)
Do in vitro assays in rat primary neurons predict drug-induced seizure liability in humans?
2018, Toxicology and Applied PharmacologyCitation Excerpt :The in vitro assay was more sensitive, with an increase in mean firing rate at 10 μM up to 1 mM, and a clear increase of the number of network bursts starting at 1 mM. Pentylenetetrazol induced a clear effect in hippocampal slices at 2–10 mM, concentrations that are closer to those observed in vivo (Rostampour et al., 2002; Easter et al., 2007; Accardi et al., 2017). In our in vitro assay, higher concentrations of pentylenetetrazol were not tested.
The emerging role of in vitro electrophysiological methods in CNS safety pharmacology
2016, Journal of Pharmacological and Toxicological MethodsCitation Excerpt :Additionally, unlike the reductionist approach applied to recombinant expression systems, hippocampal brain slices retain the impact of endogenous microcircuits (between neurons, glia and capillaries) and signaling pathways (e.g., ion channels, GPCRs, kinases, etc.) that make it more effective at predicting unintended ADRs. In agreement with this, in vitro hippocampal slices show strong concordance with in vivo exposure values of various preclinical drug candidates and known seizurogenic agents (Easter et al., 2009; Easter, Sharp, Valentin, & Pollard, 2007; Fonck et al., 2015; Hablitz, 1984; Rostampour et al., 2002). Seizurogenic activity is not restricted to the hippocampus with epileptiform activity observed in the neocortex (Kennedy & Schuele, 2012), amygdala (Hudson et al., 1993), entorhinal cortex (Vismer, Forcelli, Skopin, Gale, & Koubeissi, 2015), thalamocortical regions (Timofeev & Steriade, 2004) and possibly cerebellum (Harvey et al., 1996).
Epileptiform response of CA1 neurones to convulsant stimulation by cyclothiazide, kainic acid and pentylenetetrazol in anaesthetized rats
2011, SeizureCitation Excerpt :First, the concentration of PTZ given by i.c.v. was already 10 times higher than CTZ (5 μmol), which did successfully induce epileptiform activities, used in the same preparation in our current study. Secondly, the PTZ dose we used (upto 50 μmol) proximally reached to a local concentration of ∼25 mM, if the total rat brain extracellular fluid volume was estimated at 2 mL, which was much higher than that commonly used to induce epileptiform activities in in vitro concentration controlled studies (3–10 mM of PTZ).36–38 Thus, we hypothesize that PTZ may work as a convulsant by its metabolites instead while central injection of PTZ failed to produce such metabolites.
Pharmacological validation of a semi-automated in vitro hippocampal brain slice assay for assessment of seizure liability
2007, Journal of Pharmacological and Toxicological MethodsSeizure liability assessments using the hippocampal tissue slice: Comparison of non-clinical species
2018, Journal of Pharmacological and Toxicological MethodsCitation Excerpt :Thus, due to its role within the clinical setting and wide use as an animal seizure model (Loscher, 1997), we set out to identify the PTZ-sensitivity of hippocampal tissue isolated from several common animal models. In agreement with previously published data which, uncovered an active PTZ concentration range within the ex-vivo hippocampal tissue slice of 2–10 mM (Easter et al., 2007; Leweke, Louvel, Rausche, & Heinemann, 1990; Omrani, Fathollahi, Mohajerani, & Semnanian, 2000; Rostampour et al., 2002), this investigation demonstrated an active concentration range between 3 and 10 mM for PTZ within rats, dogs and NHPs. Interestingly, minipigs did not show any statistically significant increases in in vitro seizurogenic indicators (e.g. PS area and number) (Gutnick, Connors, & Prince, 1982) at the concentration ranges tested.