Alzheimer’s disease (AD), a progressive form of dementia, is characterized by the increased expression of secreted phospholipase A₂ group IIA (GIIA) in the affected tissue and the dysfunction of neuronal mitochondria, similar to that induced by an orthologous GIIA from snake venom, β-neurotoxic ammodytoxin (Atx), in the motor neurons. To advance our knowledge about the role of GIIA in AD, we studied the effect of rat GIIA on the neuronal mitochondria and compared it with that of the Atx. We produced recombinant rat GIIA (rGIIA) and its enzymatically inactive mutant, rGIIA(D49S), and demonstrated that they interact with the subunit II of cytochrome c oxidase (CCOX-II) as Atx. rGIIA and rGIIA(D49S) bound to this essential constituent of the respiratory chain complex with an approximately 100-fold lower affinity than Atx; nevertheless, both rGIIA molecules potently inhibited the CCOX activity in the isolated rat mitochondria. Like Atx, rGIIA was able to reach the mitochondria in the PC12 cells from the extracellular space, independent of its enzymatic activity. Consistently, the inhibition of the CCOX activity in the intact PC12 cells and in the rat’s brain tissue sections was clearly demonstrated using rGIIA(D49S). Our results show that the effects of mammalian and snake venom β-neurotoxic GIIA on the neuronal mitochondria have similar molecular backgrounds. They suggest that the elevated extracellular concentration of GIIA in the AD tissue drives the translocation of this enzyme into local neurons and their mitochondria to inhibit the activity of the CCOX in the respiratory chain. Consequently, the process of oxidative phosphorylation in the neurons is attenuated, eventually leading to their degeneration. Atx was thus revealed as a valuable molecular tool for further investigations of the role of GIIA in AD.

Ketamine has gained significant attention as a fast-acting antidepressant. However, ketamine is also associated with undesirable side effects. In our preclinical study, we explored the behavioral effects of ketamine enantiomers at subanesthetic doses. During repeated intermittent treatment, we examined locomotor stimulation and sensitization, ataxia, and expression of natural behaviors (grooming and rearing). Male Wistar rats were subcutaneously treated repeatedly with either 5 mg/kg of R-ketamine or S-ketamine, 15 mg/kg of R-ketamine, S-ketamine or racemic ketamine, 30 mg/kg of racemic ketamine or saline every third day for three weeks (seven treatments overall). After the first treatment, only 15 mg/kg of S-ketamine induced locomotor stimulation, and both 15 mg/kg of S-ketamine and 30 mg/kg of racemic ketamine induced ataxia. Upon repeated administration, doses of 15 mg/kg of R-ketamine, S-ketamine, and racemic ketamine, as well as 30 mg/kg of racemic ketamine, stimulated locomotion. 15 mg/kg of R-ketamine, S-ketamine, and racemic ketamine additionally resulted in locomotor sensitization. The last administration of 15 mg/kg of S-ketamine, 15 mg/kg of racemic ketamine, and 30 mg/kg of racemic ketamine resulted in ataxia. In the case of 15 mg/kg of S-ketamine, ataxic effects were significantly weaker in comparison to the effects from the first administration, indicating tolerance. Natural behaviors were attenuated after 5 and 15 mg/kg of S-ketamine and 15 and 30 mg/kg of racemic ketamine. Neither of the R-ketamine doses produced such an effect. We conclude that S-ketamine has a stronger behavioral effect than R-ketamine.

Treatment with levodopa (L-dopa) in Parkinson’s disease (PD) leads to involuntary movements termed L-dopa-induced dyskinesia (LID). There are contradictory data about the influence of hormone therapy in female PD patients with LID and of 17-β-estradiol (E2) on animal correlates of LID-abnormal involuntary movements (AIMs). Our aim was to characterize the influence of E2 on motor impairment and AIMs in ovariectomized 6-hydroxydopamine (6-OHDA) rat model of PD. Half of the rats received empty and the other half implants filled with E2. Following the 6-OHDA surgery, the rats received daily treatment with either L-dopa or saline for 16 days. They were assessed for AIMs, contralateral rotations, and FAS. In the L-dopa-treated rats, E2 intensified and prolonged AIMs and contralateral rotations. On the other hand, it had no effect on motor impairment. Postmortem tyrosine hydroxylase immunostaining revealed an almost complete unilateral lesion of nigrostriatal dopaminergic neurons. E2 partially prevented the upregulation of striatal ΔFosB caused by dopamine depletion. L-dopa potentiated the upregulation of ΔFosB within the dopamine-depleted striatum and this effect was further enhanced by E2. We speculate that the potentiating effects of E2 on AIMs and on contralateral rotations could be explained by the molecular adaptations within the striatal medium spiny neurons of the direct and indirect striatofugal pathways.

Ketamine, a fast-acting antidepressant, is a racemic mixture, composed of equal amounts of R- and S-ketamine. Preclinical studies are comparing them to better understand their role in therapeutic and undesirable effects. An important research gap is that studies do not use long clinically relevant protocols to compare the desired and undesired effects of ketamine enantiomers in modeled and control animals. In our preclinical study, we explored the behavioral effects of R- and S-ketamine at 10 mg/kg in clinically relevant treatment protocol using Wistar-Kyoto rats as a depression model and Wistar rats as a control. Undesirable psychomotor effects were evaluated with locomotor stimulation and sensitization, ataxia, and stereotypy. Persistent effects associated with therapeutic outcomes were evaluated by measuring working memory, anxiety, and behavioral despair. We found that S-ketamine has stronger acute psychomotor effects compared to R-ketamine and that Wistar-Kyoto rats are more sensitive to these effects compared to Wistar rats. After repeated treatment, sensitization to locomotor stimulating effects, and tolerance to ataxic effects of S-ketamine develops. We found no persistent changes due to ketamine treatments. Taken together, our results may indicate that depressed patients would be more prone to negative side effects of ketamine, compared to healthy controls. However, after repeated treatment, tolerance to side effects may develop and make the treatment more tolerable. Future preclinical and clinical studies are needed to address neurobiological mechanisms and clinical relevance of higher sensitivity to the psychomotor effects of ketamine, and the development of tolerance to psychomotor effects of ketamine in depressed individuals.

Parkinson's disease (PD) is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. Dopamine precursor L-dopa is used as the first-line treatment for PD. Evidence suggests neuroprotective effects of estrogens in PD. Since both E2 and L-dopa act as regulators of prolactin secretion from the pituitary gland, we investigated their effect on the expression of prolactin (PRL) in prolactinomas that developed in ovariectomized hemiparkinsonian rats treated with 17b-estradiol (E2). We also investigated the effect of E2 and L-dopa on the expression of synaptotagmin IV (Syt IV), an immediate early gene whose product is abundant in the pituitary gland and was found to be highly co-expressed with PRL in lactotrophs (> 90%). The hemiparkinsonian rat model was obtained by unilateral lesioning of dopaminergic nigrostriatal neurons. Rats received silastic tubing implants with E2 and were treated with L-dopa. ELISA and immunohistochemistry were used to assess the serum concentrations of PRL and E2 and expression of PRL and SytIV in the tissue of adenohypophysis, respectively. We found that high levels of serum 17b-estradiol were associated with the upregulation of Syt IV and PRL in PRL-ir cells, while treatment with L-dopa decreased the size of prolactinomas and downregulated Syt IV but had no effect on PRL expression or serum concentrations.

Zusammenfassung Das auditorische Orientierungsverhalten von Grillen ist eine komplexe senso-motorische Schleife, die von der Gesangswahrnehmung und Gesangserkennung bis hin zur Motorik der ausgelösten Steuerbewegungen reicht. Paarungsbereite Grillenweibchen laufen zu den singenden Männchen und benutzen deren Lockgesang als sensorischen Wegweiser. Dieses Verhalten, genannt Phonotaxis, ist auf des Zeitmuster des Männchengesangs abgestimmt. Doch während der Phonotaxis verändert sich die Selektivität des Verhaltens und die Tiere steuern reflexartig auch zu nichtattraktiven Lautpulsen. An den auditorischen Steuerbewegungen sind die Vorderbeine beteiligt, indem insbesondere die kontralaterale Tibia in Richtung der Schallquelle gestreckt wird. In den slow und fast Motoneuronen, die die Steuerbewegungen der Tibia kontrollieren, erhöht sich während rhythmischer Motoraktivität der zytosolische Kalziumspiegel in Phase mit den Motorsalven. Die Motoneurone erhalten keine direkten auditorischen Eingänge, sie zeigen aber bei elektrischer Reizung der Halskonnektive eine überschwellige synaptische Antwort. In laufenden Weibchen lösen identifizierte deszendierende Hirnneurone bei intrazellulärer Reizung starke Drehbewegungen aus und sind möglicherweise an der Richtungskontrolle des phonotaktischen Laufens beteiligt.