[Nimodipine in treatment of bipolar disorder]

The purpose of this review is to correlate current data on the molecular mechanisms of action of the drug Nimodipine with its clinical effects and applicability in mental disorders belonging to the spectrum of affective pathology. The article discusses the prospects for using the calcium channel blocker nimodipine as a method of both mono and combination therapy for bipolar disorders with various types of course. Nimodipine is a selective blocker of voltage-dependent calcium channels, a dihydropyridine derivative. By blocking L type calcium channels, it prevents the entry of calcium ions into the cell. Due to its pronounced ability to penetrate the blood-brain barrier, it has a selective effect on brain neurons and has a vasodilating, antihypertensive and normotimic effect. Nimodipine blocks LTCC channels in brain neurons, thereby influencing synaptic plasticity, transmitter release and excitation-transcription coupling, which makes it possible to influence various clinical conditions with pathology in the area of affect, including bipolar disorders with ultra-rapid cycling, and also, in cases with high resistance and intolerance to other mood stabilizers.

The Control of Rat Hippocampal Gamma Oscillation Strength by BK Channel Activity

Neuronal network oscillations in the gamma frequency band (30-80 Hz, γ oscillations) are associated with the higher brain functions such as perception, attention, learning and memory. BK channels mediate rapid repolarization and fast afterhyperpolarization in neurons and control neuronal excitability, and potentially control hippocampal γ oscillations. In this study, we examined the effects of modulating BK channels on hippocampal γ oscillations in the absence or presence of Ca²⁺ influx through voltage-gated Ca²⁺ channels (VGCC) or Ca²⁺-permeable AMPA receptors (CP-AMPAR). We found that blocking BK channels enhanced γ power, without affecting oscillation frequency or regularity, suggesting that BK channel activity suppresses γ oscillations. Blocking either VGCC or CP-AMPAR itself enhanced γ power, and completely occluded the effect of BK channel blockers on γ oscillations, whereas blocking BK channels first could not prevent a further γ power increase upon blockade of either CP-AMPAR or VGCC. We propose that Ca²⁺ influx through VGCC or CP-AMPAR during γ oscillations, cause membrane BK channel activation and regulate hippocampal γ oscillation strength by negative feedback.

Dorsal-Ventral Differences in Modulation of Synaptic Transmission in the Hippocampus

Functional diversification along the longitudinal axis of the hippocampus is a rapidly growing concept. Modulation of synaptic transmission by neurotransmitter receptors may importantly contribute to specialization of local intrinsic network function along the hippocampus. In the present study, using transverse slices from the dorsal and the ventral hippocampus of adult rats and recordings of evoked field postsynaptic excitatory potentials (fEPSPs) from the CA1 stratum radiatum, we aimed to compare modulation of synaptic transmission between the dorsal and the ventral hippocampus. We found that transient heterosynaptic depression (tHSD, <2 s), a physiologically relevant phenomenon of regulation of excitatory synaptic transmission induced by paired stimulation of two independent inputs to stratum radiatum of CA1 field, has an increased magnitude and duration in the ventral hippocampus, presumably contributing to increased input segregation in this segment of the hippocampus. GABA_B receptors, GABA_A receptors, adenosine A1 receptors and L-type voltage-gated calcium channels appear to contribute differently to tHSD in the two hippocampal segments; GABA_BRs play a predominant role in the ventral hippocampus while both GABA_BRs and A1Rs play important roles in the dorsal hippocampus. Activation of GABA_B receptors by an exogenous agonist, baclofen, robustly and reversibly modulated both the initial fast and the late slow components of excitatory synaptic transmission, expressed by the fEPSPslope and fEPSP decay time constant (fEPSP_τ), respectively. Specifically, baclofen suppressed fEPSP slope more in the ventral than in the dorsal hippocampus and enhanced fEPSP_τ more in the dorsal than in the ventral hippocampus. Also, baclofen enhanced paired-pulse facilitation in the two hippocampal segments similarly. Blockade of GABA_B receptors did not affect basal paired-pulse facilitation in either hippocampal segment. We propose that the revealed dorsal-ventral differences in modulation of synaptic transmission may provide a means for specialization of information processing in the local neuronal circuits, thereby significantly contributing to diversifying neuronal network functioning along the dorsal-ventral axis of hippocampus.

Large-conductance Ca2+-activated potassium channels are potently involved in the inverse neurovascular response to spreading depolarization

Recurrent spreading depolarizations occur in the cerebral cortex from minutes up to weeks following acute brain injury. Clinical evidence suggests that the immediate reduction of cerebral blood flow in response to spreading depolarization importantly contributes to lesion progression as the wave propagates over vulnerable tissue zones, characterized by potassium concentration already elevated prior to the passage of spreading depolarization. Here we demonstrate with two-photon microscopy in anesthetized mice that initial vasoconstriction in response to SD triggered experimentally with 1 M KCl is coincident in space and time with the large extracellular accumulation of potassium, as shown with a potassium indicator fluorescent dye. Moreover, pharmacological manipulations in combination with the use of potassium-sensitive microelectrodes suggest that large-conductance Ca²⁺-activated potassium (BK) channels and L-type voltage-gated calcium channels play significant roles in the marked initial vasoconstriction under elevated baseline potassium. We propose that potassium efflux through BK channels is a central component in the devastating neurovascular effects of spreading depolarizations in tissue at risk.

L-type calcium channels refine the neural population code of sound level

The coding of sound level by ensembles of neurons improves the accuracy with which listeners identify how loud a sound is. In the auditory system, the rate at which neurons fire in response to changes in sound level is shaped by local networks. Voltage-gated conductances alter local output by regulating neuronal firing, but their role in modulating responses to sound level is unclear. We tested the effects of L-type calcium channels (Ca_L: Ca_V1.1-1.4) on sound-level coding in the central nucleus of the inferior colliculus (ICC) in the auditory midbrain. We characterized the contribution of Ca_L to the total calcium current in brain slices and then examined its effects on rate-level functions (RLFs) in vivo using single-unit recordings in awake mice. Ca_L is a high-threshold current and comprises ∼50% of the total calcium current in ICC neurons. In vivo, Ca_L activates at sound levels that evoke high firing rates. In RLFs that increase monotonically with sound level, Ca_L boosts spike rates at high sound levels and increases the maximum firing rate achieved. In different populations of RLFs that change nonmonotonically with sound level, Ca_L either suppresses or enhances firing at sound levels that evoke maximum firing. Ca_L multiplies the gain of monotonic RLFs with dynamic range and divides the gain of nonmonotonic RLFs with the width of the RLF. These results suggest that a single broad class of calcium channels activates enhancing and suppressing local circuits to regulate the sensitivity of neuronal populations to sound level.