Opposite effects of internal globus pallidus stimulation on pallidal neurones activity.

Besides clinical efficacy, the mechanisms of action of deep brain stimulation (DBS) are still debated. To shed light on this complex issue, we have taken the opportunity to record the response of globus pallidus internus (GPi) neurones to 100 Hz stimulations in a case of Lesch-Nyhan syndrome (LNS) where four pallidal electrodes were implanted. Three types of response were observed, 2/19 neurones were unaffected by DBS. About 7/19 neurones were inhibited during DBS stimulation and 10/19 neurones were excited during DBS stimulation. Both effects ceased when DBS was turned off. Inhibited neurones were situated lower that exited ones on the trajectory (1.25 and 4.65 mm above the center of GPi respectively). These observations suggest that locally DBS induces a reversible inhibition of neurone firing rate while at the same time distantly exciting the main afferents to and/or efferents from the GPi. Both actions would result in a strong GPi inhibition that does not preclude increased outflow from the GPi.     

In vitro neuroendocrine effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the AhR-expressing hypothalamic rat GnV-3 cell line

The aryl hydrocarbon receptor (AhR) is involved in a wide variety of biological and toxicological responses, including neuroendocrine signaling. Due to the complexity of neuroendocrine pathways in e.g. the hypothalamus and pituitary, there are limited in vitro models available despite the strong demand for such systems to study and predict neuroendocrine effects of chemicals. In this study, the applicability of the AhR-expressing rat hypothalamic GnV-3 cell line was investigated as a novel model to screen for neuroendocrine effects of AhR ligands using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as reference compound. The qRT-PCR analyses demonstrated the presence of several sets of neurotransmitter receptors in the GnV-3 cells. TCDD (10 nM) altered neurotransmitter signaling by up-regulation of glutamate (Grik2), gamma-amino butyric acid (Gabra₂) and serotonin (Ht_2C) receptor mRNA levels. However, no significant changes in basal and serotonin-evoked intracellular Ca²⁺ concentration ([Ca²⁺]_i) or serotonin release were observed. On the other hand, TCDD de-regulated period circadian protein homolog 1 (Per1) and gonadotropin releasing hormone (Gnrh) mRNA levels within a 24-h time period. Both Per1 and Gnrh genes displayed a similar mRNA expression pattern in GnV-3 cells. Moreover, the involvement of AhR in TCDD-induced alteration of Neuropeptide Y (Npy) gene expression was found and confirmed by using siRNA targeted against Ahr in GnV-3 cells. Overall, the combined results demonstrate that GnV-3 cells may be a suitable model to predict some mechanisms of action and effects of AhR ligands in the hypothalamus.     

Interactions of Dopamine with Glutamate- and GABA-mediated Synaptic Transmission in the Rat Entorhinal Cortex In Vitro

We have studied the interactions between dopamine and glutamate-mediated transmission in the entorhinal cortex using intracellular recording in a slice preparation from the rat brain. High concentrations (0.1 – 1 mM) of dopamine had weak, direct effects on the membrane potential with predominantly hyperpolarizing responses in layer II neurons and depolarizing responses in layer V. Studies with the dopamine antagonists sulpiride (D2 antagonist, 10 – 50 μM) and SCH-23390 (D1 antagonist, 50 μM) indicated that the hyperpolarization by dopamine could be mediated by D2 receptors, although the pharmacology was not clear-cut. The depolarizing response was not affected by either D1 or D2 antagonists. Synaptic responses of layer II and layer V cells were complex, consisting of both inhibitory and excitatory potentials. In untreated slices, dopamine reduced all components of the synaptic responses. However, when components of the responses were pharmacologically isolated, only the excitatory, glutamate-mediated potentials were consistently affected and the GABAergic inhibitory potentials were more resistant to reduction by dopamine. Excitatory potentials mediated by both N -methyl- d -aspartate and α-amino-3-hydroxy-5-methyl-isoxazolepropionic acid receptors were reduced by dopamine, but the former were more strongly affected. Studies with antagonists suggested that the D1 receptor is more likely to be involved in the decrement of glutamate transmission. Thus, dopamine appears to modulate glutamate-mediated synaptic transmission in the entorhinal cortex, and it is conceivable that a disturbance in this interaction could be involved in the aetiology of schizophrenia.     

Suppression of kindled seizures by paracrine adenosine release from stem cell-derived brain implants

PURPOSE: Stem cells and their derivatives have emerged as a promising tool for cell-based drug delivery because of (a) their unique ability to differentiate into various somatic cell types, (b) the virtually unlimited donor source for transplantation, and (c) the advantage of being amenable to a wide spectrum of genetic manipulations. Previously, adenosine-releasing embryonic stem (ES) cells have been generated by disruption of both alleles of adenosine kinase (Adk-/-). Lack of ADK did not compromise the cells' differentiation potential into embryoid bodies or glial precursor cells. The aim of the present study was to investigate the potential of differentiated Adk-/- ES cell progeny for seizure suppression by paracrine adenosine release. METHODS: To isolate paracrine effects of stem cell-derived implants from effects caused by network integration, ES cell-derived embryoid bodies and glial precursor cells were encapsulated into semipermeable polymer membranes and grafted into the lateral brain ventricles of kindled rats. RESULTS: While seizure activity in kindled rats with wild-type Adk+/+ implants remained unaltered, rats with adenosine-releasing Adk-/- ES cell-derived implants displayed transient protection from convulsive seizures and a profound reduction of afterdischarge activity in EEG recordings. Long-term seizure suppression was precluded by limited viability of the encapsulated cells. CONCLUSIONS: We thereby provide a proof-of-principle that Adk-/- ES cell-derived brain implants can suppress seizure activity by a paracrine mode of action. Adk-deficient stem cells therefore represent a potential tool for the treatment of epileptic disorders.     

Hypogonadism in a patient with a mutation in the luteinizing hormone beta-subunit gene

A 30-year-old man who presented with delayed puberty and infertility was found to have hypogonadism associated with an absence of circulating luteinizing hormone. The patient had a homozygous missense mutation in the gene that encodes the beta subunit of luteinizing hormone (Gly36Asp), a mutation that disrupted a vital cystine knot motif and abrogated the heterodimerization and secretion of luteinizing hormone. Treatment with human chorionic gonadotropin increased circulating testosterone, promoted virilization, and was associated with the appearance of normal spermatozoa in low concentrations. This case illustrates the important physiological role that luteinizing hormone plays in male sexual maturation and fertility.     

Involvement of amygdala networks in epileptiform synchronization in vitro

We used field potential and intracellular recordings in rat brain slices that included the hippocampus, a portion of the basolateral/lateral nuclei of the amygdala (BLA) and the entorhinal cortex (EC). Bath application of the convulsant 4-aminopyridine (50 microM) to slices (n=12) with reciprocally connected areas, induced short-lasting interictal-like epileptiform discharges that (i) occurred at intervals of 1.2-2.8 s, (ii) originated in CA3, and (iii) spread to EC and BLA. Cutting the Schaffer collaterals abolished them in both parahippocampal areas where slower interictal-like (interval of occurrence=4-17 s) and prolonged ictal-like discharges (duration=15+/-6.9 s, mean+/-S.D., n=7) appeared. These new types of epileptiform activity originated in either EC or BLA. Similar findings were obtained in slices (n=19) in which the hippocampus outputs were not connected with the EC and BLA under control conditions. Cutting the EC-BLA connections made independent slow interictal- and ictal-like activities appear in both areas (n=5). NMDA receptor antagonism (n=6) abolished ictal-like discharges and reduced the duration of the slow interictal-like events. Repetitive stimulation of BLA at 0.5-1 Hz in Schaffer collateral cut slices, induced interictal-like epileptiform depolarizations in EC and reversibly blocked ictal-like activity (n=14). Thus, CA3 outputs in intact slices entrain EC and BLA networks into an interictal-like pattern that inhibits the propensity of these parahippocampal areas to generate prolonged ictal-like paroxysms. Accordingly, NMDA receptor-dependent ictal-like events are initiated in BLA or EC once the propagation of CA3-driven interictal-like discharges to these areas is abated by cutting the Schaffer collaterals. Similar inhibitory effects also occur by activating BLA outputs directed to EC at rates that mimic the CA3-driven interictal-like pattern.     

Selective effects of PPARγ agonists and antagonists on human pre‐adipocyte differentiation

Aim: The insulin sensitizer rosiglitazone (RTZ) acts by activating peroxisome proliferator and activated receptor γ (PPAR γ), an effect accompanied in vivo in humans by an increase in fat storage. We hypothesized that this effect concerns PPARγ₁ and PPARγ₂ differently and is dependant on the origin of the adipose cells (subcutaneous or visceral). To this aim, the effect of RTZ, the PPARγ antagonist GW9662 and lentiviral vectors expressing interfering RNA were evaluated on human pre‐adipocyte models. Methods: Two models were investigated: the human pre‐adipose cell line Chub‐S7 and primary pre‐adipocytes derived from subcutaneous and visceral biopsies of adipose tissue (AT) obtained from obese patients. Cells were used to perform oil‐red O staining, gene expression measurements and lentiviral infections. Results: In both models, RTZ was found to stimulate the differentiation of pre‐adipocytes into mature cells. This was accompanied by significant increases in both the PPARγ₁ and PPARγ₂ gene expression, with a relatively stronger stimulation of PPARγ₂. In contrast, RTZ failed to stimulate differentiation processes when cells were incubated in the presence of GW9662. This effect was similar to the effect observed using interfering RNA against PPARγ₂. It was accompanied by an abrogation of the RTZ‐induced PPARγ₂ gene expression, whereas the level of PPARγ₁ was not affected. Conclusions: Both the GW9662 treatment and interfering RNA against PPARγ₂ are able to abrogate RTZ‐induced differentiation without a significant change of PPARγ₁ gene expression. These results are consistent with previous results obtained in animal models and suggest that in humans PPARγ₂ may also be the key isoform involved in fat storage.     

Quality index for the quantification of the information recorded along standard microelectrode tracks to the subthalamic nucleus in parkinsonian patients.

OBJECTIVE: To quantify the usefulness of the neuronal activity recorded on a standard microelectrode track to the subthalamic nucleus (STN) for the determination of the transition between the thalamus and the STN. METHODS: The study is based on analysis of 689 extracelullar single units recorded on 70 tracks passing through the thalamus and the STN. Using four neuron parameters that were correlated with electrode depth, a quality index (QI) for each track was computed and compared with the subjective assessment by the electrophysiologist of the track quality. RESULTS: Subjectively, the transition between the thalamus and the STN was detected in 49 tracks (usual track) and not detected on 21 tracks (unusual tracks). Objectively, spike frequency, cell burst index (BI), signal relative root mean square (RMS) and spike relative amplitude were correlated with electrode depth and used to compute track QI. The average QI index of usual and unusual tracks was 0.25 +/- 0.9 and 0.85 +/- 0.15 (mean +/- confidence interval at P < 0.001), respectively. In 20 patients, QI correlates with post-operative measurement of electrode length in the STN. CONCLUSION: These results demonstrate that simple statistical analysis taking into account the variation of single-unit characteristics with electrode depth can discriminate between useful and useless tracks for the determination of the STN localisation.