A translational EEG-based approach to assess modulation of long-lasting NMDAR-dependent synaptic plasticity.

BACKGROUND: NYX-2925 is a novel N-methyl-D-aspartate receptor (NMDAR) modulator that has been shown to facilitate both NMDAR-dependent long-term potentiation (LTP) in vitro and learning and memory in vivo. OBJECTIVE: The present studies examine the effects of NYX-2925 on NMDAR-dependent auditory LTP (aLTP) in vivo. METHODS: NMDAR-dependent aLTP and NMDAR-dependent auditory mismatch negativity (MMN) was measured, as well as changes in resting-state qEEG power. RESULTS: NYX-2925 (1, 10 mg/kg PO) increased aLTP 1 h after auditory tetanus measured by the post- minus pre-tetanus difference waveform 140-180 ms post tone onset. NYX-2925 (0.1, 1 mg/kg PO) facilitated MMN measured by the difference waveform (i.e., deviant minus standard tones). NYX-2925 (0.1, 1, 10 mg/kg PO) also enhanced resting-state alpha qEEG power. Conversely, the NMDAR glutamate site antagonist CPP (10 mg/kg IP) reduces alpha power and MMN and produces an opposite effect as NYX-2925 on aLTP. CONCLUSIONS: Together, these data suggest that the activation of the NMDAR by NYX-2925 enhances synaptic plasticity in vivo, which may both reduce symptoms of neurological disorders and serve as a biomarker for drug effects. This is the first demonstration of a long-lasting (1-h post-tetanus) effect of NMDAR modulation on synaptic plasticity processes in vivo using a noninvasive technique in freely behaving animals.

Changes in the amount and structure of motor variability during a deboning process are associated with work experience and neck-shoulder discomfort.

In this field study, the size and structure of kinematics variability were assessed in relation to experience and discomfort during a deboning task. Eighteen workers divided in groups with low/high experience and with/without neck-shoulder discomfort participated. Standard deviation and coefficient of variation (amount of variability), as well as approximate entropy and sample entropy (complexity) and, correlation dimension (dimensionality) were computed for head-shoulder, shoulder-hip and elbow-hip displacement in the vertical direction. A longer work experience was associated with shorter work cycle duration and decreased amount of variability while complexity increased for the head-shoulder displacement, P<0.05. Shorter work cycle, lower amount of variability and, lower dimensionality for the head-shoulder displacement were found in relation to discomfort, P<0.05. While the amount of variability, complexity and dimensionality increased for the elbow-hip displacement, P<0.05. These findings suggest a functional role of experience via learning effects and discomfort through compensatory mechanisms on the size and structure of motor variability.

Electroconvulsive therapy in melancholia: the role of hippocampal neurogenesis.

OBJECTIVE: To elucidate the relationship between the effects of electroconvulsive therapy (ECT) on hippocampal anatomy and function in the therapy of melancholic depression and preclinical observations of increased neurogenesis in the hippocampus of experimental animals receiving electroconvulsive seizures (ECS). We emphasize the role of hypercortisolaemia in melancholic depression and in experimental hippocampal neurogenesis. METHOD: Our statements are based on a variety of studies pointing to i) ECT being superior to all other treatment modalities in the therapy of melancholia, ii) melancholia being associated with hypercortisolaemia and iii) evidence of hippocampal neurogenesis being relevant for understanding both melancholia and ECT. RESULTS: The increased neurogenesis found in animal studies shows stronger effect of seizures than of antidepressant drugs. The onset of effect is not only faster but is also sustained. Newborn cells are found to be functional. Suppression of neurogenesis by chronic treatment with corticosterone is associated with depression-like biology and behaviour making comparison with human depression and its response to ECT relevant. CONCLUSION: We hypothesize that the superior antimelancholic effect of induced seizures may be understood in the light of the powerful control of neural plasticity exerted by the regulation of the hypothalamic-pituitary-adrenal axis and, perhaps, other regulatory factors.

Arrested neuronal proliferation and impaired hippocampal function following fractionated brain irradiation in the adult rat.

The generation of new neurons in the adult mammalian brain has been documented in numerous recent reports. Studies undertaken so far indicate that adult hippocampal neurogenesis is related in a number of ways to hippocampal function.Here, we report that subjecting adult rats to fractionated brain irradiation blocked the formation of new neurons in the dentate gyrus of the hippocampus. At different time points after the termination of the irradiation procedure, the animals were tested in two tests of short-term memory that differ with respect to their dependence on hippocampal function. Eight and 21 days after irradiation, the animals with blocked neurogenesis performed poorer than controls in a hippocampus-dependent place-recognition task, indicating that the presence of newly generated neurons may be necessary for the normal function of this brain area. The animals were never impaired in a hippocampus-independent object-recognition task. These results are in line with other reports documenting the functional significance of newly generated neurons in this region. As our irradiation procedure models prophylactic cranial irradiation used in the treatment of different cancers, we suggest that blocked neurogenesis contributes to the reported deleterious side effects of this treatment, consisting of memory impairment, dysphoria and lethargy.

Intrahippocampal infusion of antisense oligodeoxynucleotide to the GABA(A) receptor gamma2 subunit enhances neuropeptide Y gene expression.

The effects of hippocampal treatment with a phosphorothioate oligodeoxynucleotide (ODN) antisense to the gamma-aminobutyric acid (GABA)A receptor gamma2 subunit on neuropeptide Y (NPY) were studied. Adult male Wistar rats were treated with unilateral intrahippocampal infusion of gamma2 subunit antisense ODN for 5 days. Rats infused with mismatch ODN and naïve rats served as controls. Brain sections were analysed for levels of NPY mRNA by in situ hybridisation, NPY-immunoreactivity (NPY-ir) by means of immunocytochemistry, and specific NPY binding sites by in vitro receptor autoradiography. Following infusion of antisense ODN, a marked increase in cytoplasmic NPY-ir was observed in hilar neurones of the fascia dentata. Further, intense NPY-ir was visualised in the mossy fibres and in cell bodies of the entorhinal cortex and throughout the neocortex. High levels of NPY mRNA were detected in the same cortical areas of antisense treated rats. A very large increase was observed in the piriform and parietal areas. NPY gene expression also occurred in the granular cell layer, in which no NPY mRNA could be detected in normal animals. The level and distribution of cells displaying high levels of NPY mRNA differed among animals, perhaps as a result of the distinct anatomical location of ODN infusion. Finally, hippocampal levels of NPY specific binding increased, suggesting that NPY neurotransmission is markedly increased. These findings are reminiscent of reported changes in the expression of NPY mRNA and immunoreactivity in conditions of increased neuronal excitation and support the usefulness of the present animal model for the study of epileptic phenomena.

Increased neurogenesis in a model of electroconvulsive therapy.

BACKGROUND: Electroconvulsive therapy (ECT) is a widely used and efficient treatment modality in psychiatry, although the basis for its therapeutic effect is still unknown. Past research has shown seizure activity to be a regulator of neurogenesis in the adult brain. This study examines the effect of a single and multiple electroconvulsive seizures on neurogenesis in the rat dentate gyrus. METHODS: Rats were given either a single or a series of 10 electroconvulsive seizures. At different times after the seizures, a marker of proliferating cells, Bromodeoxyuridine (BrdU), was administered to the animals. Subsequently, newborn cells positive for BrdU were counted in the dentate gyrus. Double staining with a neuron-specific marker indicated that the newborn cells displayed a neuronal phenotype. RESULTS: A single electroconvulsive seizure significantly increased the number of new born cells in the dentate gyrus. These cells survived for at least 3 months. A series of seizures further increased neurogenesis, indicating a dose-dependent mechanism. CONCLUSIONS: We propose that generation of new neurons in the hippocampus may be an important neurobiologic element underlying the clinical effects of electroconvulsive seizures.

Electroconvulsive stimuli enhance both neuropeptide Y receptor Y1 and Y2 messenger RNA expression and levels of binding in the rat hippocampus.

Repeated electroconvulsive stimulations and other seizure modalities produce an increase in neuropeptide Y synthesis and local release in the rat hippocampus, and perhaps as a consequence, a change in the concentration of neuropeptide Y binding sites in the same region. The aim of the present study was to determine possible changes in the expression of neuropeptide Y receptor subtypes affected by repeated stimulations in the hippocampus. Rats were exposed to 14 daily stimulations, and the brains were removed 24h after the last stimulation. For in vitro receptor autoradiography and in situ hybridisation histochemistry, the brains were frozen, sectioned, and levels of neuropeptide Y binding sites and messenger RNA expressions were determined quantitatively on sections from the same animals. In order to determine the contribution of different neuropeptide Y receptor subtypes, serial sections were incubated with either 125I-labelled peptide YY alone or the same radio-labelled peptide mixed with an excess of a number of displacing compounds with affinity for either neuropeptide Y receptor subtype Y1, Y2, or both. Binding studies revealed that the majority of peptide YY binding sites was represented by Y2, and that electroconvulsive stimulations reduced the binding capacity or the concentration of this receptor. A prominent reduction of Y1-preferring binding sites was determined in the dentate gyrus, and to a lesser extent in the CA1 and CA3 regions. Similarly, the treatment produced a significant reduction of Y2-preferring binding sites in the CA1 and CA3 region, but not in the granular cell layer of the dentate gyrus. Using semi-quantitative in situ hybridization, Y1 receptor messenger RNA level in the granular cell layer of the dentate increased by the stimulations. In the same region, Y2 receptor messenger RNA was expressed in low to undetectable amounts, but after the repeated stimulations, this transcript was found in moderate to high levels. These data suggest that the neuropeptide Yergic system in the dentate gyrus and the pyramidal cell layer are affected by the treatment, and that this includes both Y1 and Y2 receptor subtypes. Because levels of messenger RNA and binding are distinctly regulated, the turnover of both Y1 and Y2 molecules is strongly increased under electroconvulsive stimulations, suggesting that the intrahippocampal neuropeptide Yergic neurotransmission is also increased under the stimulations.

Kainic acid seizure suppression by neuropeptide Y is not correlated to immediate early gene mRNA levels in rats.

Kainic acid induces seizures and a rapid induction of immediate early genes and neuronal death. Neuropeptide Y (NPY) is implicated in seizure inhibiting activity. In order to investigate the mechanisms by which NPY inhibits seizure activity, this study was carried out to measure the levels of mRNAs encoding three different immediate early genes, in regions of the hippocampus and relate their induction to the behaviour in the same animals. NPY inhibited both the time spent in seizures, and the number of generalized seizures. However, NPY did not inhibit the induction of c-fos, FosB or junB mRNA in any hippocampal region examined in the same animals, showing lack of correlation between immediate early gene induction and seizure activity.

Electrical amygdala kindling in alcohol-withdrawal kindled rats.

Repeated alcohol withdrawal has been shown to kindle seizure activity. The purpose of the present investigation was to study electrical amygdala kindling in rats previously exposed to alcohol-withdrawal kindling. In three independent experiments, male Wistar rats were subjected to multiple episodes each consisting of 2 days of severe alcohol intoxication and 5 days of alcohol withdrawal. In the first experiment, the alcohol-withdrawal kindled animals were divided into two groups depending on whether spontaneous alcohol-withdrawal seizures were observed in episodes 10-13. In the second and third experiments, the alcohol-withdrawal kindled animals were compared to a group in which alcohol-withdrawal kindling was prevented by diazepam treatment during the withdrawal reactions in order to discriminate between the effect of withdrawal and intoxication. Electrical kindling was initiated 28-35 days after the last alcohol dose by exposing the animals to daily electrical stimulations of the right amygdala. The results showed that amygdala kindling was facilitated in alcohol-withdrawal kindled animals which showed spontaneous withdrawal seizure activity, compared with animals exposed to multiple episodes of alcohol withdrawal which did not develop withdrawal seizures or with animals exposed to a single episode of alcohol intoxication. When compared to the control group, the alcohol-withdrawal kindled group with seizures also kindled at a faster rate, but the difference did not reach statistical significance and therefore the results must be regarded as preliminary at present.

Neuropeptide Y attenuates naloxone-precipitated morphine withdrawal via Y5-like receptors.

The effects of intracerebroventricular injection of neuropeptide Y (NPY) and various NPY-related peptides were studied on naloxone-precipitated withdrawal from morphine in rats. The withdrawal reaction was assessed using an overall motor score, including jumping, wet dog shakes and other motor-related signs as well as a nonmotor score. At doses of 3, 6 or 12 nmol, NPY strongly and dose-dependently reduced the motor score. A less prominent inhibitory effect was revealed on the nonmotor score. At 6 nmol, [Leu31,Pro34]-NPY, NPY 3-36, peptide YY and human pancreatic polypeptide all significantly attenuated the motor score, whereas NPY 13-36 was without effect. This pharmacological profile suggests that the antiwithdrawal effect of NPY is mediated via the recently cloned Y5 receptor. Our data are consistent with a potential role for NPY and Y5-like receptors in basic mechanisms and as a therapeutic target in opioid dependence and withdrawal.

Powerful inhibition of kainic acid seizures by neuropeptide Y via Y5-like receptors.

Neuropeptide Y (NPY) is widely distributed in interneurons of the central nervous system (CNS), including the hippocampus and cerebral cortex, in concentrations exceeding those of any other known neuropeptides. Sequence data comparing different species show that NPY is highly conserved. This suggests a critical role in regulation of regional neuronal excitability. Kainic acid, a glutamate agonist at kainic acid receptors, causes severe limbic motor seizures culminating in status epilepticus. We here report that NPY administered into the lateral ventricle is a powerful inhibitor of motor as well as electroencephalographic (EEG) seizures induced by kainic acid. This effect was mediated via receptors with a pharmacological profile similar to the recently cloned rat Y5 receptor. The present study is the first to demonstrate that NPY possesses anticonvulsant activity. This is consistent with the concept that NPY is an endogenous anticonvulsant and suggests that agonists acting at Y5-like receptors may constitute a novel group of drugs in antiepileptic therapy.

Neuropeptide Y inhibits hippocampal seizures and wet dog shakes.

The effects of intracerebroventricular neuropeptide Y (NPY) or somatostatin were studied upon hippocampal EEG seizures elicited by electrical stimulation of the rat dentate gyrus or subiculum. At doses of 6 and 12 nmol, the latter dose being more effective, NPY reduced the primary afterdischarge duration (1.ADD) and almost completely abolished the secondary afterdischarge. The reduction in 1.ADD resulted from an increase in afterdischarge threshold. The reduction in secondary afterdischarge duration was independent of a reduction in 1.ADD. This implies that NPY not only exerts antiepileptiform effects in the dentate gyrus and subiculum, but also in areas to which epileptiform EEG activity spreads before reverberating. In addition, NPY strongly reduced seizure-related 'wet dog shakes' (WDS). This is consistent with previous studies showing that the dentate gyrus is essential for the generation of WDS. However, NPY inhibited WDS even when 1.ADDs were evoked which did not differ from those of vehicle rats, indicating extra-dentate inhibition by NPY as well. No effects were seen with somatostatin. These results show that NPY exerts antiepileptiform effects in vivo, suggesting that increased NPY in the hippocampal formation observed after seizures is a compensatory anti-seizure response.

Regulation of synaptic ribbons in rat pineal gland explants by norepinephrine and sympathetic neurons in a co-culture model.

The hypothesis that synaptic ribbons in the mammalian pinealocyte are influenced by adrenergic mechanisms was tested in the present study using a co-culture model of pineal glands and superior cervical ganglia from neonatal rats. Pineal gland explants survived and showed a high degree of differentiation when cultured for up to 30 days regardless of the presence or absence of superior cervical ganglia. Pineal glands also had neurotrophic properties promoting the survival and neurite extension from superior cervical ganglia. Synaptic ribbons were a common ultrastructural feature in all pineal cultures. There was a significant decline in synaptic ribbon numbers when co-cultured with superior cervical ganglia for both 7 and 30 days. A similar significant decrease in synaptic ribbon frequency was observed after treatment of pineal explants with norepinephrine (10(-5 )M) for both 7 and 30 days. These findings are consistent with the hypothesis that neural mechanisms play an important role in regulating synaptic ribbon numbers, at least during early development. The study also illustrates the utility of pineal gland-superior cervical ganglia co-cultures as a model for future investigations of neuron-target interactions in the pineal.

Neurotrophic effects of the pineal gland: role of non-neuronal cells in co-cultures of the pineal gland and superior cervical ganglia.

The pineal gland (PG) is a source of several trophic factors. In this study, PG and superior cervical ganglia (SCG) from Sprague-Dawley neonates (1-day-old) were co-cultured to test the hypothesis that endogenous release of PG NGF (or an NGF-like cytokine) is sufficient to promote survival of SCG neurons. Neuronal density of SCG neurons was significantly enhanced when co-cultured with PG for 7 days compared to SCG cultured alone. SCG survival and neurite formation in PG co-cultures was less than in SCG treated with exogenous NGF (100 ng/ml). The neurotrophic effect of PG co-cultures was abolished when 1% anti-NGF was added to the medium. Co-cultures of SCG neurons with established 7-day PG cultures induced extensive SCG neurite formation within 24 hr compared to SCG co-cultured with 1-day PG cultures. This suggests that PG neurotrophic effects are due to PG non-neuronal cells (nnc) that proliferate to confluency by 7 days in culture. S-antigen-positive pinealocytes did not proliferate in culture. There was decreased SCG survival when neurons were seeded onto PG cultures that had been previously killed by drying, which suggests that the neurotrophic effects of nnc are not substrate-dependent. Immunocytochemical characterization of PG nnc revealed a heterogenous mixture of astrocytes, macrophage/microglia, and fibroblasts. These findings support the hypothesis that NGF is actively secreted by PG and that nnc are the principal source of this neurotophin.