Brivaracetam does not alter spatial learning and memory in both normal and amygdala-kindled rats.

Several antiepileptic drugs (AEDs) may induce memory deficits when tested in preclinical models at doses that exert significant protection against seizures. Brivaracetam (BRV) is a novel high-affinity SV2A ligand also displaying inhibitory activity at neuronal voltage-gated sodium channels. In the present study we have investigated the effects of BRV, at doses that exerted marked anticonvulsant effects in kindled rats, upon cognitive functioning and memory in both normal and amygdala-kindled rats using place learning version of Morris water maze. In addition the effect of BRV on long-term potentiation (LTP) in rat hippocampal slices has been investigated. BRV (2.1, 6.8 or 21.0mg/kg i.p.) was injected daily, 60min before each session. Results indicated that in both normal and amygdala-kindled rats BRV did not alter the latency to find the hidden platform or swimming speed during the four consecutive days of learning. Similarly, the time spent in the target quadrant, used as a further independent index of spatial memory, was not modified by BRV treatment. Likewise, BRV did not affect the LTP induction in CA1 hippocampal region when tested at 3-30microM concentration range, which had been demonstrated to significantly reduce epileptiform activity in slice models. Based on the results of the present study it can be expected that BRV will not have detrimental effects on hippocampal-dependent cognitive functions in patients with epilepsy.

Levetiracetam does not modulate neuronal voltage-gated Na+ and T-type Ca2+ currents.

This study investigated whether the mechanism of action of levetiracetam (LEV) is related to effects on neuronal voltage-gated Na+ or T-type Ca2+currents. Rat neocortical neurones in culture were subjected to the whole-cell mode of voltage clamping under experimental conditions designed to study voltage-gated Na+ current. Additionally, visually identified pyramidal neurones in the CA1 area of rat hippocampal slices were subjected to the whole-cell mode of voltage clamping under experimental conditions designed to study low-voltage-gated (T-type) Ca2+ current. LEV (10 microM-1 mM) did not modify the Na+ current amplitude and did not change (200 microM) the steady-state activation and inactivation, the time to peak, the fast kinetics of the inactivation and the recovery from the steady-state inactivation of the Na+ current. Likewise, LEV (32-100 microM) did not modify the amplitude and did not change the steady-state activation and inactivation, the time to peak, the fast kinetics of the inactivation and the recovery from the steady-state inactivation of the T-type Ca2+current. In conclusion, neuronal voltage-gated Na+ channels do not appear directly involved in the antiepileptic mechanism of action of LEV, and LEV was devoid of effect on the low-voltage-gated (T-type) Ca2+ current in hippocampal neurones.

Levetiracetam inhibits the high-voltage-activated Ca(2+) current in pyramidal neurones of rat hippocampal slices.

The effect of the new antiepileptic drug levetiracetam (LEV; KEPPRA) on the neuronal high-voltage-activated (HVA) Ca(2+) current was investigated on pyramidal neurones, visually identified in the CA1 area of rat hippocampal slices. Nystatin-perforated patch clamp recordings were made under experimental conditions designed to study HVA Ca(2+) currents. The HVA current, activated by steadily increasing voltage-ramps, was reversibly eliminated by Cd(2+) and depressed by either nimodipine, or omega-Conotoxin GVIA. After 30 min perfusion of the slices with LEV 32 microM, the current decayed to 55+/-9% (mean+/-SEM; n=9) of the initial value, which is significantly (P<0.05, two-tailed t-test) lower than the rundown to 84+/-10% in a control group (n=10) of neurones. The limited, but significant depression of the neuronal HVA Ca(2+) current, produced by LEV at a clinically relevant concentration, might contribute to the antiepileptic action of the drug.

Chronic electrode implantation entails epileptiform field potentials in rat hippocampal slices, similarly to amygdala kindling.

Evoked field potentials were recorded in the CA3, CA1 and dentate gyrus (DG) of hippocampal slices from amygdala kindled, non-stimulated amygdala electrode-implanted, and non-implanted age-matched rats to evaluate the consequences on hippocampal neuronal networks of kindling stimulation versus electrode implantation. No overt modification of field potentials was detected in either the CA1 or the DG areas. In contrast, a very significant increase in the occurrence of repetitive population spikes evoked by single stimuli was detected in the CA3 area in slices from both amygdala kindled and non-stimulated amygdala implanted rats. The epileptiform pattern of CA3 field potentials was at least as well expressed in implanted non-stimulated, as in kindled rats, suggesting that electrode implantation has a major contribution to this marker of epileptogenesis.

Properties of T-type calcium current in enkephalinergic neurones in guinea-pig hypothalamic slices.

The guinea-pig hypothalamic magnocellular dorsal nucleus (mdn) exclusively contains enkephalinergic neurones providing inputs to the septum. This nucleus is believed to play a role in hippocampo-septo-hypothalamic relationships. mdn neurones display prominent low-threshold Ca2+ spikes, which differ in their propensity to trigger either a burst of Na+ spikes or a single spike. In the present study, whole-cell voltage-clamp experiments were carried out on thick slices at 34 degrees C to characterize the pharmacological and physical properties of the transient Ca2+ current (IT) underlying the low-threshold spikes. Recorded cells were dye-labelled and identified as belonging to the mdn. In bursting and non-bursting neurones, IT was reduced by amiloride (1 microM) and octanol (1 mM), and during replacement of Ca2+ by Ba2+. The Ca2+ channel blocker mibefradil (10 microM) had only a slight blocking action. Nifedipine (100 microM) and flunarizine (1 microM) had no effect. IT activated between -80 mV and -50 mV and the mean peak current was 1050 pA. Steady-state activation and inactivation curves were fitted by a Boltzmann equation. The half-activation voltage was -70 mV, slope factor=3.6, and half-inactivation voltage was about -80 mV, slope factor=4.5. Time-to-peak and time constant of inactivation were voltage dependent. Recovery from activation occurred within 500 ms. When compared with results on other IT, the present data show that the current possesses distinct pharmacological and physical properties. Nevertheless, all investigated cells displayed a homogenous profile of IT, suggesting that the differences in spike pattern between mdn neurones are not due to different populations of Ca2+ channels.

Hippocampal slices from long-term streptozotocin-injected rats are prone to epileptiform responses.

Evoked field potentials were recorded in the CA3, CA1 and dentate gyrus (DG) regions of hippocampal slices from rats injected with streptozotocin (STZ; 60 mg/kg i.p.), to detect whether STZ-induced diabetes entails changes in hippocampal excitability. No change in hippocampal responsiveness was observed in slices from diabetic rats, up to 3 weeks post-STZ. Repetitive population spikes (PSs) reminiscent of an epileptiform hyperexcitability were, however, recorded in CA3 > CA1 > DG areas after more than 4 weeks ('long-term') post-STZ, although the maximal amplitudes were not different in STZ-diabetic versus control rats. Intracellular recordings on CA3 pyramidal neurons confirmed that fimbrial stimulation evokes significantly more action potentials in neurons from 'long-term' STZ-diabetic versus control rats. This is the first report of the appearance of repetitive hippocampal responses, particularly in the seizure-prone CA3 area, as a long-term consequence of hyperglycemic STZ treatment in rat.

Electrophysiology of the neurons in the area of the enkephalinergic magnocellular dorsal nucleus of the guinea-pig hypothalamus, studied by intracellular and whole-cell recordings.

The electrophysiological characteristics of 103 hypothalamic neurons in the area of the guinea-pig enkephalinergic magnocellular dorsal nucleus were studied in a thick slice preparation with sharp microelectrodes (63 neurons) and patch pipettes for whole-cell recordings (40 neurons). Of the sampled cells, 79.6% displayed tetrodotoxin-resistant, calcium-dependent slow-depolarizing potentials when the membrane potential was hyperpolarized to approximately -70 mV (type I neurons). Half of them showed robust slow depolarizing potentials, generating bursts of fast action potentials. In the remaining neurons, the slow-depolarizing potentials did not cause burst-firing action potentials but triggered single action potentials. The other class of neurons (20.4% of the sample: type II neurons) did not exhibit calcium-dependent slow-depolarizing potentials. Resting potential, input resistance and the membrane time constant did not distinguish among the two classes of neurons. Current-voltage relationships were heterogeneous. A transient outward rectification was observed in the two classes. This was not totally blocked by 2 mM 4-aminopyridine but was abolished when using perfusion with cobalt instead of calcium. Input resistance and the time constant were higher when measured in the whole-cell mode but the other electrical parameters and the sampling of the recorded neurons were strikingly similar between the two methods of recording. Intracellular staining of 22 neurons retrogradely labelled from the lateral septum allowed confirmation of their location within the magnocellular dorsal nucleus. The study indicates that the electrical properties of these neurons did not differ from those of neurons found throughout the area explored. It also indicates the presence of distinct electrophysiological types of cells in the magnocellular dorsal nucleus, although the nucleus is composed of a single type of enkephalinergic neuron. It provides a basis for the study of the regulation of activity of the neurons at the origin of an enkephalinergic tractus which is involved in neuroendocrine, psychoneuroendocrine and immune processes.