The functional organization of excitatory synaptic input to place cells

Hippocampal place cells contribute to mammalian spatial navigation and memory formation. Numerous models have been proposed to explain the location-specific firing of this cognitive representation, but the pattern of excitatory synaptic input leading to place firing is unknown, leaving no synaptic-scale explanation of place coding. Here we used resonant scanning two-photon microscopy to establish the pattern of synaptic glutamate input received by CA1 place cells in behaving mice. During traversals of the somatic place field, we found increased excitatory dendritic input, mainly arising from inputs with spatial tuning overlapping the somatic field, and functional clustering of this input along the dendrites over ~10 µm. These results implicate increases in total excitatory input and co-activation of anatomically clustered synaptic input in place firing. Since they largely inherit their fields from upstream synaptic partners with similar fields, many CA1 place cells appear to be part of multi-brain-region cell assemblies forming representations of specific locations.

Abnormal Sleep Architecture and Hippocampal Circuit Dysfunction in a Mouse Model of Fragile X Syndrome

Fragile X syndrome (FXS) is the most common heritable cause of intellectual disability and single-gene cause of autism spectrum disorder. The Fmr1 null mouse models much of the human disease including hyperarousal, sensory hypersensitivity, seizure activity, and hippocampus-dependent cognitive impairment. Sleep architecture is disorganized in FXS patients, but has not been examined in Fmr1 knockout (Fmr1-KO) mice. Hippocampal neural activity during sleep, which is implicated in memory processing, also remains uninvestigated in Fmr1-KO mice. We performed in vivo electrophysiological studies of freely behaving Fmr1-KO mice to assess neural activity, in the form of single-unit spiking and local field potential (LFP), within the hippocampal CA1 region during multiple differentiated sleep and wake states. Here, we demonstrate that Fmr1-KO mice exhibited a deficit in rapid eye movement sleep (REM) due to a reduction in the frequency of bouts of REM, consistent with sleep architecture abnormalities of FXS patients. Fmr1-KO CA1 pyramidal cells (CA1-PCs) were hyperactive in all sleep and wake states. Increased low gamma power in CA1 suggests that this hyperactivity was related to increased input to CA1 from CA3. By contrast, slower sharp-wave ripple events (SWRs) in Fmr1-KO mice exhibited longer event duration, slower oscillation frequency, with reduced CA1-PC firing rates during SWRs, yet the incidence rate of SWRs remained intact. These results suggest abnormal neuronal activity in the Fmr1-KO mouse during SWRs, and hyperactivity during other wake and sleep states, with likely adverse consequences for memory processes.

Impaired hippocampal ripple-associated replay in a mouse model of schizophrenia

The cognitive symptoms of schizophrenia presumably result from impairments of information processing in neural circuits. We recorded neural activity in the hippocampus of freely behaving mice that had a forebrain-specific knockout of the synaptic plasticity-mediating phosphatase calcineurin and were previously shown to exhibit behavioral and cognitive abnormalities, recapitulating the symptoms of schizophrenia. Calcineurin knockout (KO) mice exhibited a 2.5-fold increase in the abundance of sharp-wave ripple (SWR) events during awake resting periods and single units in KO were overactive during SWR events. Pairwise measures of unit activity, however, revealed that the sequential reactivation of place cells during SWR events was completely abolished in KO. Since this relationship during postexperience awake rest periods has been implicated in learning, working memory, and subsequent memory consolidation, our findings provide a mechanism underlying impaired information processing that may contribute to the cognitive impairments in schizophrenia.

A heuristic method for finding the optimal number of clusters with application in medical data

In this paper, a heuristic method for determining the optimal number of clusters is proposed. Four clustering algorithms, namely K-means, Growing Neural Gas, Simulated Annealing based technique, and Fuzzy C-means in conjunction with three well known cluster validity indices, namely Davies-Bouldin index, Calinski-Harabasz index, Maulik-Bandyopadhyay index, in addition to the proposed index are used. Our simulations evaluate capability of mentioned indices in some artificial and medical datasets.

Determination of amphotericin B in cerebrospinal fluid by solid-phase extraction and liquid chromatography

A highly sensitive and reproducible liquid chromatography (LC) method for the determination of Amphotericin B in cerebrospinal fluid has been developed and validated. This LC-based method involves using nystatin as an internal standard and solid-phase extraction for sample preparation, followed by reversed-phase separation monitored by absorbance at 410 nm. The method has a limit of quantification of less than 1 ng ml-1 and excellent precision and accuracy, with both percentage relative standard deviation and percentage relative error less than 10%. The established linearity range was 1-10 ng ml-1 (r2 > 0.99). The extraction recovery of Amphotericin B from the cerebrospinal fluid is higher than 90% over the entire linear range. The method has been successfully employed for studying the penetration of Amphotericin B into the central nervous system in dogs and human.

Bioavailability studies of drugs with nonlinear pharmacokinetics: II. Absolute bioavailability of intravenous phenytoin prodrug at therapeutic phenytoin serum concentrations determined by double-stable isotope technique

Measurement of the absolute bioavailability of phenytoin (PHT) derived from test doses of phenytoin prodrug (PPD) at therapeutic PHT serum concentrations is complicated by two problems: 1) the area under the serum concentration versus time curve (AUC) produced by a given size of test dose will vary directly with background PHT serum concentration due to the nonlinear pharmacokinetic properties of PHT; 2) PPD is more water soluble than PHT, making renal excretion of PPD more likely. The authors describe a double-stable isotope method that obviates these two problems. Using only six subjects, the authors were able to demonstrate bioequivalence of PHT derived from intravenous PPD with intravenous PHT by current FDA standards for AUC ratio of test/reference formulation (90% confidence intervals between 0.80 and 1.20; ratio > or = 0.80 in > or = 80% of subjects; statistical power to detect a difference of 0.20 with a probability of 0.80).

Simultaneous determination of p-hydroxylated and dihydrodiol metabolites of phenytoin in urine by high-performance liquid chromatography

Accurate urinary measurements of the two major metabolites of phenytoin, 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) and 5-(3,4-dihydroxy-cyclohexa-1,5-dienyl)-5-phenylhydantoin (dihydrodiol, DHD), are necessary for pharmacokinetic and drug-interaction studies of this commonly used antiepileptic drug. We describe a simple, rapid, acid hydrolysis, with liquid-liquid extraction and simultaneous isocratic reversed-phase high-performance liquid chromatography of p-HPPH and 5-(m-hydroxyphenyl)-5-phenylhydantoin (m-HPPH) (hydrolytic end product of DHD). p-HPPH and m-HPPH were quantitated against their separate respective internal standards of alphenal and tolylbarb. The mobile phase consisted of water-dioxane-tetrahydrofuran (80:15:5, v/v/v) at 2 ml/min and at 50 degrees C, with detection at 225 nm. Baseline separation was achieved by use of a 16 cm x 3.9 mm Nova-Pak C18 column and total analysis time of 12 min. p-HPPH and m-HPPH concentrations ranged from 10 to 200 and from 2 to 30 micrograms/ml, respectively, with between-day coefficients of variations of 3.3-4.5% and 2.2-5.1% for controls. All standard curves were linear with r values greater than 0.993. The DHD concentration was determined by multiplying m-HPPH concentrations by 2.3.

GM1 gangliosides alter acute MPTP-induced behavioral and neurochemical toxicity in mice

We investigated the effect of GM1 gangliosides on a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson disease. Five groups of mice (saline, GM1 (30 mg/kg), MPTP, MPTP + GM1 (15 mg/kg), MPTP + GM1 (30 mg/kg] were compared. GM1 was given daily via intraperitoneal injection before and during 13 daily doses of MPTP (30 mg/kg). Mice were tested for locomotion (1) within 2 h of an MPTP dose (to measure reduced motor activity), and (2) within 24 h of an MPTP dose (after animals had recovered and exhibited hyperactivity). We found that mice given GM1 gangliosides exhibited significantly less MPTP-induced behavior. This effect was most evident with the 15 mg/kg GM1 dose. GM1 also appeared to attenuate MPTP-induced neurochemical changes. GM1 effects indicating enhancement of DA turnover and preservation of DA, DOPAC and HVA concentrations in the striatum were found after the 8th MPTP dose. These latter neurochemical changes, however, were transient and not present after the 13th MPTP dose. Our data would suggest that gangliosides may reduce acute MPTP-induced neurotoxicity in mice either through an increase in DA neuron survival and/or the augmentation of striatal DA activity.

Magnitude of response to levodopa in Parkinson disease as it relates to peripheral and central measurements of levodopa and associated metabolites

The relationships between magnitude of response to orally administered carbidopa/levodopa (CD/LD) and serum/cerebrospinal fluid (CSF) concentrations of levodopa (LD), 3-O-methyldopa (3-O-MD), and homovanillic acid (HVA) were studied in 15 patients with chronic LD-treated Parkinson disease. The degree of clinical benefit derived from a 25/250 tablet of CD/LD could not be correlated with absolute serum levels of LD, 3-O-MD or LD/3-O-MD ratios. CSF levels of LD and 3-O-MD were also not associated with improvement. CSF levels of HVA, however, did significantly correlate with magnitude of response to LD. Furthermore, CSF HVA levels were not dependent on previous LD dosage. Our data suggest that in chronic LD-treated patients, central factors related to the integrity of the nigrostriatal tract may be a more important determinant of magnitude of response to LD than peripheral elements affecting the amount of LD entering the central nervous system.

Bioavailability of ACC-9653 (phenytoin prodrug)

The bioavailability of phenytoin from ACC-9653 versus intravenously administered sodium phenytoin was determined using a crossover design for intravenous and intramuscular administration of ACC-9653 to healthy volunteers. Absolute bioavailability of phenytoin derived from ACC-9653 in each subject was calculated as the ratio of the phenytoin area under the plasma concentration time curve for time 0 to infinity [AUC(0-inf)] after ACC-9653 divided by the phenytoin AUC(0-inf) after intravenous sodium phenytoin. The mean absolute bioavailability of ACC-9653 was 0.992 after intravenous administration and 1.012 after intramuscular administration. These data establish that the bioavailability of ACC-9653 is complete following intravenous or intramuscular administration in single-dose volunteer studies. The absolute bioavailability of phenytoin derived from ACC-9653 in subjects with therapeutic plasma phenytoin concentrations is being studied in patients given simultaneous infusions of stable isotope-labeled tracer doses of ACC-0653 and sodium phenytoin.