Negligible In Vitro Recovery of Macromolecules from Microdialysis Using 100 kDa Probes and Dextran in Perfusion Fluid.

Microdialysis is applied in neurointensive care to monitor cerebral glucose metabolism. If recoverable, macromolecules may also serve as biomarkers in brain disease and provide clues to their passage across the blood-brain barrier. Our study aimed to investigate the in vitro recovery of human micro- and macromolecules using microdialysis catheters and perfusion fluids approved for clinical use. In vitro microdialysis of a bulk solution containing physiological or supraphysiological concentrations of glucose, lactate, pyruvate, human IgG, serum albumin, and hemoglobin was performed using two different catheters and perfusion fluids. One had a membrane cut-off of 20 kDa and was used with a standard CNS perfusion fluid, and the other had a membrane cut-off of 100 kDa and was perfused with the same solution supplemented with dextran. The flow rate was 0.3 µl/min. We used both push and push-pull methods. Dialysate samples were collected at 2-h intervals for 6 h and analyzed for relative recovery of each substance. The mean relative recovery of glucose, pyruvate, and lactate was > 90% in all but two sets of experiments. In contrast, the relative recovery of human IgG, serum albumin, and hemoglobin from both bulk solutions was below the lower limit of quantification (LLOQ). Using a push-pull method, recovery of human IgG, serum albumin, and hemoglobin from a bulk solution with supraphysiological concentrations were above LLOQ but with low relative recovery (range 0.9%-1.6%). In summary, exchanging the microdialysis setup from a 20 kDa catheter with a standard perfusion fluid for a 100 kDa catheter with a perfusion solution containing dextran did not affect the relative recovery of glucose and its metabolites. However, it did not result in any useful recovery of the investigated macromolecules at physiological levels, either with or without a push-pull pump system.

The effect of ketamine and D-cycloserine on the high frequency resting EEG spectrum in humans.

RATIONALE: Preclinical studies indicate that high-frequency oscillations, above 100 Hz (HFO:100-170 Hz), are a potential translatable biomarker for pharmacological studies, with the rapid acting antidepressant ketamine increasing both gamma (40-100 Hz) and HFO. OBJECTIVES: To assess the effect of the uncompetitive NMDA antagonist ketamine, and of D-cycloserine (DCS), which acts at the glycine site on NMDA receptors on HFO in humans. METHODS: We carried out a partially double-blind, 4-way crossover study in 24 healthy male volunteers. Each participant received an oral tablet and an intravenous infusion on each of four study days. The oral treatment was either DCS (250 mg or 1000 mg) or placebo. The infusion contained 0.5 mg/kg ketamine or saline placebo. The four study conditions were therefore placebo-placebo, 250 mg DCS-placebo, 1000 mg DCS-placebo, or placebo-ketamine. RESULTS: Compared with placebo, frontal midline HFO magnitude was increased by ketamine (p = 0.00014) and 1000 mg DCS (p = 0.013). Frontal gamma magnitude was also increased by both these treatments. However, at a midline parietal location, only HFO were increased by DCS, and not gamma, whilst ketamine increased both gamma and HFO at this location. Ketamine induced psychomimetic effects, as measured by the PSI scale, whereas DCS did not increase the total PSI score. The perceptual distortion subscale scores correlated with the posterior low gamma to frontal high beta ratio. CONCLUSIONS: Our results suggest that, at high doses, a partial NMDA agonist (DCS) has similar effects on fast neural oscillations as an NMDA antagonist (ketamine). As HFO were induced without psychomimetic effects, they may prove a useful drug development target.

Sleep patterning changes in a prenatal stress model of depression.

Clinical depression is accompanied by changes in sleep patterning, which is controlled in a circadian fashion. It is thus desirable that animal models of depression mirror such diurnally-specific state alterations, along with other behavioral and physiological changes. We previously found several changes in behavior indicative of a depression-like phenotype in offspring of rats subjected to repeated, variable prenatal stress (PNS), including increased locomotor activity during specific periods of the circadian cycle. We, therefore, investigated whether PNS rats also exhibit alterations in sleep/wakefulness behavior around the change from light-to-dark phase. Control and PNS Sprague-Dawley rats were implanted with electrodes for continuous monitoring of electroencephalic activity used to determine behavioral state. The distribution of slow-wave sleep (SWS), rapid eye movement sleep (REMS) and wakefulness was compared for periods before and after lights were turned off, between baseline conditions and after exposure to an acute stressor. Both REMS and SWS amounts were increased in PNS rats relative to control animals in the beginning of the dark phase. REMS changes were due to an increase in REMS bout number, rather than in bout duration. During this circadian time period, we did not find any sex differences in the state changes. These results indicate that PNS affects baseline sleep patterning in both male and female rats around active-phase onset.

The translationally relevant mouse model of the 15q13.3 microdeletion syndrome reveals deficits in neuronal spike firing matching clinical neurophysiological biomarkers seen in schizophrenia.

AIM: To date, the understanding and development of novel treatments for mental illness is hampered by inadequate animal models. For instance, it is unclear to what extent commonly used behavioural tests in animals can inform us on the mental and affective aspects of schizophrenia. METHODS: To link pathophysiological processes in an animal model to clinical findings, we have here utilized the recently developed Df(h15q13)/+ mouse model for detailed investigations of cortical neuronal engagement during pre-attentive processing of auditory information from two back-translational auditory paradigms. We also investigate if compromised putative fast-spiking interneurone (FSI) function can be restored through pharmacological intervention using the Kv3.1 channel opener RE1. Chronic multi-array electrodes in primary auditory cortex were used to record single cell firing from putative pyramidal and FSI in awake animals during processing of auditory sensory information. RESULTS: We find a decreased amplitude in the response to auditory stimuli and reduced recruitment of neurones to fast steady-state gamma oscillatory activity. These results resemble encephalography recordings in patients with schizophrenia. Furthermore, the probability of interneurones to fire with low interspike intervals during 80 Hz auditory stimulation was reduced in Df(h15q13)/+ mice, an effect that was partially reversed by the Kv3.1 channel modulator, RE1. CONCLUSION: This study offers insight into the consequences on a neuronal level of carrying the 15q13.3 microdeletion. Furthermore, it points to deficient functioning of interneurones as a potential pathophysiological mechanism in schizophrenia and suggests a therapeutic potential of Kv3.1 channel openers.

Neonatal exposure to low-dose domoic acid lowers seizure threshold in adult rats.

Exposing Sprague-Dawley rat pups to very low, sub-convulsant doses of domoic acid (DOM) during perinatal development has been previously shown to result in seizure-like activity in adulthood similar to partial complex epilepsy in humans, and to produce cellular and molecular changes in the dentate gyrus and area CA-3 of the hippocampus. To further these investigations we recorded electroencephalographical and behavioural activity in DOM and control rats following a normally sub-convulsant dose (25 mg/kg) of pentylenetetrazol. During this exposure, 50% of DOM-treated rats experienced a Stage V (tonic-clonic) seizure (X(2)((1))=5.33, P=0.021), indicating a lowering of generalized seizure threshold in these animals. In a separate experiment we explored focal seizure (afterdischarge) threshold as well as seizure propagation rates in treated rats, using a 25 consecutive day standard amygdala kindling paradigm. We report that the afterdischarge threshold for DOM-treated rats was significantly lower than controls (F((1,27))=7.117, P=0.013). No difference between groups was found in seizure progression as measured by afterdischarge duration, latency to first Stage V seizure, or latency to reach a fully kindled state (defined as five consecutive Stage V seizures). Timm staining to assess mossy fibre sprouting (MFS) in the hippocampus revealed a significant MFS increase relative to sham at the ventral level in both left and right inner molecular layer of the dentate gyrus for all DOM-treated animals, as well as in the dorsal stratum oriens of CA3 contralateral to electrode placement, and these increases were further enhanced by the kindling procedure. We conclude that perinatal exposure to subconvulsive doses of DOM results in permanent changes in neuronal excitability in the adult rat, as demonstrated by a lowering of both generalized seizure and focal afterdischarge threshold, and produces increased MFS following kindling.

Reductions in paradoxical sleep time in adult rats treated neonatally with low dose domoic acid.

One hallmark of neurological dysfunction is a reduction in paradoxical sleep (PS) time. To determine if adult rats treated neonatally with low dose domoic acid have altered sleep patterns, a home cage analysis of electroencephalogram (EEG) waveforms was performed using radio telemetry. Domoate treated rats spent significantly less time in PS than controls during daytime hours even though they spent the same total amount of time sleeping, and showed no difference in stage shifts into the PS stage.