Lubica Lacinova

Homocysteine is a non-proteinogenic amino acid formed during the metabolism of methionine to cysteine and plays a critical role in maintaining cellular homeostasis. Although multiple enzymatic pathways tightly regulate homocysteine levels, their dysfunction can lead to elevated circulating homocysteine, which is recognized as a risk factor for various cardiovascular and neurological disorders. While most evidence linking homocysteine to specific pathologies comes from observational studies, emerging data suggest that dysregulation of ion channels may be an important underlying mechanism. In this review, we summarize the effects of homocysteine on the expression and function of key ion channel families including calcium, sodium, and potassium channels, and discuss their potential pathophysiological implications.

When accompanied by excessive exposure to the stressors, pregnancy may result in prenatal depression, that has in turn negative influence on the offspring’s brain. Mirtazapine, among other antidepressants, is commonly used to treat prenatal depression. Even though mirtazapine is generally considered safe for pregnant women, its effect on the offspring brain have not been sufficiently investigated. The present study aimed to examine the effects of chronic unpredictable stress (CUS) in pregestational rats, perinatal mirtazapine treatment, and their combination, on offspring behavior and brain function. We assessed offspring anxiety levels during the elevated plus maze (EPM) test, the expression of pro-neuroplastic proteins in the offspring brain, the excitability of brainstem monoamine and hippocampal glutamate neurons, and the expression and activity of ryanodine receptors (RyR2). Surprisingly, maternal pregestational stress induced an anxiolytic-like effect in the offspring. This anxiolytic effect was associated with an increased excitability of serotonin (5-HT) neurons and detected in the offspring of the vehicle-, but not mirtazapine-treated dams. Perinatal mirtazapine, however, elevated expression of the brain-derived neurotrophic factor (BDNF); this effect was detected in the female offspring of the stressed dams. Regarding the offspring glutamate and dopamine neurons, the combination of maternal stress and mirtazapine inhibited their burst firing, potentially, due to decreased expression of the glutamate receptors. Even though calcium signaling is important for the burst firing of the neurons, the effects of maternal stress and mirtazapine on the burst activity of the offspring glutamate and dopamine might not be mediated via mechanism(s) involving the RyR2. Summarizing, mirtazapine may diminish the negative influence of maternal stress and depression on the offspring brain, via mechanism(s) putatively involving 5-HT neurotransmission and BDNF.

Elevated plasma homocysteine (Hcy) levels lead to hyperhomocysteinemia, a condition associated with various neurological disorders affecting multiple brain regions, including the hippocampus. In this study, we investigated the effects of exposing cultured rat hippocampal neurons to Hcy concentrations corresponding to mild, moderate, and severe hyperhomocysteinemia. A short 24-hour exposure had minimal effects, whereas prolonged exposure up to 14 days moderately enhanced hippocampal excitability without altering the gene expression of voltage-dependent calcium, sodium, or potassium channels or intracellular calcium levels. These findings suggest that Hcy-induced changes in neuronal excitability may contribute to neuropathologies associated with hyperhomocysteinemia.

Maternal depression negatively affects the neurodevelopment of offspring, but its pharmacological treatment during gestation remains controversial. This study reports the consequences of maternal depression and/or prenatal antidepressant treatment with mirtazapine on offspring early neurodevelopment via an animal model of maternal depression induced by pregestational chronic unpredictable stress (CUS). Offspring from four groups were studied: nonstressed vehicle-treated dams, nonstressed mirtazapine-treated dams, stressed vehicle-treated dams, and stressed mirtazapine-treated dams. The hippocampal excitability of offspring was examined in primary hippocampal cultures established on the first postnatal day, reflecting mostly prenatal development, and in hippocampal slices prepared on postnatal days 11–13, reflecting an early postnatal development. The pregestational CUS modeling of maternal depression moderately suppressed offspring hippocampal excitability in primary cultures but facilitated it in slices. Mirtazapine administered to CUS-exposed dams partly rectified the changes observed in primary cultures of pups from untreated dams and, more prominently, in slices. Mirtazapine itself negatively affected the hippocampal excitability of nonstressed dam offspring in primary culture, and this effect was diminished in slices. Since altered hippocampal neurotransmission might be responsible, at least in part, for the neuropsychopathologies frequently observed in the offspring of depressed mothers, and mirtazapine was able to partly relieve such changes, this treatment may be also beneficial during the prenatal and perinatal periods.

Maternal infection during pregnancy is associated with an increased risk of neurodevelopmental disorders, including depression, schizophrenia, and autism spectrum disorder. The hippocampus plays a critical role in these disorders, but the impact of maternal immune activation (MIA) on early hippocampal neuron function remains poorly understood. We investigated the effects of lipopolysaccharide-induced MIA in pregnant rats (20–80 μg/kg on gestational days 15–19) on the electrophysiological properties of hippocampal pyramidal neurons from newborn offspring. Primary neuronal cultures were prepared from the hippocampi of newborn rats and maintained for 13 days in vitro (DIV13). Whole-cell patch-clamp recordings assessed neuronal excitability parameters between DIV4-13. MIA significantly altered action potential characteristics in offspring hippocampal neurons, including: (1) increased latency time, threshold potential, and repolarization potential; (2) decreased peak potential, ascend and descend velocities; and (3) reduced spontaneous and evoked firing frequencies. These alterations suggest impaired glutamatergic neurotransmission in the hippocampus of MIA offspring, with potential sex-specific effects observed for spontaneous activity. Our findings demonstrate that MIA significantly decreases the excitability of hippocampal pyramidal neurons in newborn offspring. This reduced glutamatergic neurotransmission may contribute to the pathophysiology of neurodevelopmental disorders associated with maternal infection during pregnancy. This study provides novel insights into early neurophysiological changes following prenatal immune challenge that may inform therapeutic interventions targeting hippocampal function.

Noxious stimuli like cold, heat, pH change, tissue damage, and inflammation depolarize a membrane of peripheral endings of specialized nociceptive neurons which eventually results in the generation of an action potential. The electrical signal is carried along a long axon of nociceptive neurons from peripheral organs to soma located in dorsal root ganglions and further to the dorsal horn of the spinal cord where it is transmitted through a chemical synapse and is carried through the spinal thalamic tract into the brain. Two subtypes of voltage-activated calcium play a major role in signal transmission: a low voltage-activated Ca_V3.2 channel and a high voltage-activated Ca_V2.2 channel. The Ca_V3.2 channel contributes mainly to the signal conductance along nociceptive neurons while the principal role of the Ca_V2.2 channel is in the synaptic transmission at the dorsal horn. Both channels contribute to the signal initiation at peripheral nerve endings. This review summarizes current knowledge about the expression and distribution of these channels in a nociceptive pathway, the regulation of their expression and gating during pain pathology, and their suitability as targets for pharmacological therapy.

Low-voltage-activated T-type Ca²⁺ channels are key regulators of neuronal excitability both in the central and peripheral nervous systems. Therefore, their recruitment at the plasma membrane is critical in determining firing activity patterns of nerve cells. In this study, we report the importance of secretory carrier-associated membrane proteins (SCAMPs) in the trafficking regulation of T-type channels. We identified SCAMP2 as a novel Ca_v3.2-interacting protein. In addition, we show that co-expression of SCAMP2 in mammalian cells expressing recombinant Ca_v3.2 channels caused an almost complete drop of the whole cell T-type current, an effect partly reversed by single amino acid mutations within the conserved cytoplasmic E peptide of SCAMP2. SCAMP2-induced downregulation of T-type currents was also observed in cells expressing Ca_v3.1 and Ca_v3.3 channel isoforms. Finally, we show that SCAMP2-mediated knockdown of the T-type conductance is caused by the lack of Ca_v3.2 expression at the cell surface as evidenced by the concomitant loss of intramembrane charge movement without decrease of total Ca_v3.2 protein level. Taken together, our results indicate that SCAMP2 plays an important role in the trafficking of Ca_v3.2 channels at the plasma membrane.

Developmental and epileptic encephalopathies (DEEs) are a group of severe epilepsies that are characterized by seizures and developmental delay. DEEs are primarily attributed to genetic causes and an increasing number of cases have been correlated with variants in ion channel genes. In this study, we report a child with an early severe DEE. Whole exome sequencing showed a de novo heterozygous variant (c.4873–4881 duplication) in the SCN8A gene and an inherited heterozygous variant (c.952G > A) in the CACNA1H gene encoding for Na_v1.6 voltage-gated sodium and Ca_v3.2 voltage-gated calcium channels, respectively. In vitro functional analysis of human Na_v1.6 and Ca_v3.2 channel variants revealed mild but significant alterations of their gating properties that were in general consistent with a gain- and loss-of-channel function, respectively. Although additional studies will be required to confirm the actual pathogenic involvement of SCN8A and CACNA1H, these findings add to the notion that rare ion channel variants may contribute to the etiology of DEEs.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the progressive loss of cortical, brain stem and spinal motor neurons that leads to muscle weakness and death. A previous study implicated CACNA1H encoding for Cav3.2 calcium channels as a susceptibility gene in ALS. In the present study, two heterozygous CACNA1H variants were identified by whole genome sequencing in a small cohort of ALS patients. These variants were functionally characterized using patch clamp electrophysiology, biochemistry assays, and molecular modeling. A previously unreported c.454GTAC > G variant produced an inframe deletion of a highly conserved isoleucine residue in Cav3.2 (p.ΔI153) and caused a complete loss-of-function of the channel, with an additional dominant-negative effect on the wild-type channel when expressed in trans. In contrast, the c.3629C > T variant caused a missense substitution of a proline with a leucine (p.P1210L) and produced a comparatively mild alteration of Cav3.2 channel activity. The newly identified ΔI153 variant is the first to be reported to cause a complete loss of Cav3.2 channel function. These findings add to the notion that loss-of-function of Cav3.2 channels associated with rare CACNA1H variants may be risk factors in the complex etiology of ALS.