Empirical mode decomposition of local field potential data from optogenetic experiments

Introduction

This study investigated the effects of cocaine administration and parvalbumin-type interneuron stimulation on local field potentials (LFPs) recorded in vivo from the medial prefrontal cortex (mPFC) of six mice using optogenetic tools.

Methods

The local network was subject to a brief 10 ms laser pulse, and the response was recorded for 2 s over 100 trials for each of the six subjects who showed stable coupling between the mPFC and the optrode. Due to the strong non-stationary and nonlinearity of the LFP, we used the adaptive, data-driven, Empirical Mode Decomposition (EMD) method to decompose the signal into orthogonal Intrinsic Mode Functions (IMFs).

Results

Through trial and error, we found that seven is the optimum number of orthogonal IMFs that overlaps with known frequency bands of brain activity. We found that the Index of Orthogonality (IO) of IMF amplitudes was close to zero. The Index of Energy Conservation (IEC) for each decomposition was close to unity, as expected for orthogonal decompositions. We found that the power density distribution vs. frequency follows a power law with an average scaling exponent of ~1.4 over the entire range of IMF frequencies 2-2,000 Hz.

Discussion

The scaling exponent is slightly smaller for cocaine than the control, suggesting that neural activity avalanches under cocaine have longer life spans and sizes.

Repeated methamphetamine administration produces cognitive deficits through augmentation of GABAergic synaptic transmission in the prefrontal cortex

Methamphetamine (METH) abuse is associated with the emergence of cognitive deficits and hypofrontality, a pathophysiological marker of many neuropsychiatric disorders that is produced by altered balance of local excitatory and inhibitory synaptic transmission. However, there is a dearth of information regarding the cellular and synaptic mechanisms underlying METH-induced cognitive deficits and associated hypofrontal states. Using PV-Cre transgenic rats that went through a METH sensitization regime or saline (SAL) followed by 7-10 days of home cage abstinence combined with cognitive tests, chemogenetic experiments, and whole-cell patch recordings on the prelimbic prefrontal cortex (PFC), we investigated the cellular and synaptic mechanisms underlying METH-induce hypofrontality. We report here that repeated METH administration in rats produces deficits in working memory and increases in inhibitory synaptic transmission onto pyramidal neurons in the PFC. The increased PFC inhibition is detected by an increase in spontaneous and evoked inhibitory postsynaptic synaptic currents (IPSCs), an increase in GABAergic presynaptic function, and a shift in the excitatory-inhibitory balance onto PFC deep-layer pyramidal neurons. We find that pharmacological blockade of D1 dopamine receptor function reduces the METH-induced augmentation of IPSCs, suggesting a critical role for D1 dopamine signaling in METH-induced hypofrontality. In addition, repeated METH administration increases the intrinsic excitability of parvalbumin-positive fast spiking interneurons (PV + FSIs), a key local interneuron population in PFC that contributes to the control of inhibitory tone. Using a cell type-specific chemogenetic approach, we show that increasing PV + FSIs activity in the PFC is necessary and sufficient to cause deficits in temporal order memory similar to those induced by METH. Conversely, reducing PV + FSIs activity in the PFC of METH-exposed rats rescues METH-induced temporal order memory deficits. Together, our findings reveal that repeated METH exposure increases PFC inhibitory tone through a D1 dopamine signaling-dependent potentiation of inhibitory synaptic transmission, and that reduction of PV + FSIs activity can rescue METH-induced cognitive deficits, suggesting a potential therapeutic approach to treating cognitive symptoms in patients suffering from METH use disorder.

161 THE ROLE OF THE GERIATRIC DAY HOSPITAL DURING THE COVID 19 PANDEMIC

Background

Methods

Results

Conclusion

163 EVALUATING THE ROLE OF THE GERIATRIC DAY HOSPITAL IN MEDICATION OPTIMISATION

Background

The geriatric day hospital (GDH) provides outpatient geriatric medical, nursing and rehabilitation care to older adults. The aim of this study was to assess whether medication optimisation occurs in this setting. We believe the GDH would be an ideal location for mediation optimisation due to the stable community dwelling patients and close follow up by specialised physicians.

Methods

Electronic patient records of the new patients ≥65 years seen in the GDH over a 3-month period were reviewed. Potentially inappropriate prescriptions (PIPs) and potentially prescribing omissions (PPOs) were identified using the STOPP/START prescribing tool on admission to the GDH and again at discharge from the GDH.

Results

One-hundred and sixty-seven patient records were reviewed; mean age 80.8 (SD6.5) years, 62.9% female, median clinical frailty scale score 6 (IQR5–6), mean number of conditions 5.79 (SD3), mean number of medications 7.57 (SD3.7). Patients had a median of 4 (IQR2–7) consultations. The number of patients prescribed at least 1 STOPP-PIP reduced by 10% (42.4% vs 38%; p < 0.001). Vasodilator drugs in patients with orthostatic hypotension were deprescribed most frequently (6.5% vs 3%; p < 0.001). PPOs were reduced by 36% (47.5% vs 30.6%;p < 0.001). The largest improvement was identified in the prescription of vitamin D in patients experiencing falls (17.4% vs 13.8%;p < 0.001). Logistic regression was performed to ascertain the influence of age, gender, falls, dementia, co-morbidity number and medication number on the likelihood of a patient experiencing a PIP or PPO. For every medication prescribed, the odds of experiencing a PIP increased by 11.8% (OR1.187, 95%CI 1.052–1.339). Being female increased the odds of experiencing a PPO by 21.7% (OR2.17, 95%CI 10.53–4.468).

Conclusion

Medication optimisation is key in avoiding side effects from potentially inappropriate medications. The frequency of patient attendances coupled with geriatricians’ expertise makes the GDH an ideal setting for medication optimisation in multi-morbid frail community-dwelling older adults.

Loss of dysbindin-1 affects GABAergic transmission in the PFC

It has been shown that dystrobrevin-binding protein 1 gene that encodes the protein dysbindin-1 is associated with risk for cognitive deficits, and studies have shown decreases in glutamate and correlated decreases in dysbindin-1 protein in the prefrontal cortex (PFC) and hippocampus of post-mortem tissue from schizophrenia patients. The PFC and the hippocampus have been shown to play a fundamental role in cognition, and studies in dysbindin-1 null mice have shown alterations in NMDAR located in pyramidal neurons as well as perturbation in LTP and cognitive deficits. The balance between excitatory and inhibitory transmission is crucial for normal cognitive functions; however, there is a dearth of information regarding the effects of loss of dysbindin-1 in GABAergic transmission. Using in vitro whole-cell clamp recordings, Western blots, and immunohistochemistry, we report here that dysbindin-1-deficient mice exhibit a significant decrease in the frequency of sIPSCs and in the amplitude of mIPSCs and significant decreases in PV staining and protein level. These results suggest that loss of dysbindin-1 affects GABAergic transmission at pre- and postsynaptic level and decreases parvalbumin markers.

Dopamine receptor antagonists effects on low-dimensional attractors of local field potentials in optogenetic mice

The goal of this study was to investigate the effects of acute cocaine injection or dopamine (DA) receptor antagonists on the medial prefrontal cortex (mPFC) gamma oscillations and their relationship to short term neuroadaptation that may mediate addiction. For this purpose, optogenetically evoked local field potentials (LFPs) in response to a brief 10 ms laser light pulse were recorded from 17 mice. D1-like receptor antagonist SCH 23390 or D2-like receptor antagonist sulpiride, or both, were administered either before or after cocaine. A Euclidian distance-based dendrogram classifier separated the 100 trials for each animal in disjoint clusters. When baseline and DA receptor antagonists trials were combined in a single trial, a minimum of 20% overlap occurred in some dendrogram clusters, which suggests a possible common, invariant, dynamic mechanism shared by both baseline and DA receptor antagonists data. The delay-embedding method of neural activity reconstruction was performed using the correlation time and mutual information to determine the lag/correlation time of LFPs and false nearest neighbors to determine the embedding dimension. We found that DA receptor antagonists applied before cocaine cancels out the effect of cocaine and leaves the lag time distributions at baseline values. On the other hand, cocaine applied after DA receptor antagonists shifts the lag time distributions to longer durations, i.e. increase the correlation time of LFPs. Fourier analysis showed that a reasonable accurate decomposition of the LFP data can be obtained with a relatively small (less than ten) Fourier coefficients.

Methamphetamine Self-Administration Elicits Sex-Related Changes in Postsynaptic Glutamate Transmission in the Prefrontal Cortex

Preclinical and clinical research has shown that females are more vulnerable to the rewarding effects of stimulants, and it has been proposed that estrogens may play a role in this enhanced sensitivity; however sex differences in methamphetamine (METH)-induced neuroplasticity have not been explored. To address this gap in knowledge, we recorded from the prelimbic area of the prefrontal cortex (PL-PFC) of male and female rats following long access METH self-administration (SA) and investigated the resulting long-term synaptic neuroadaptations. Males and females took similar amounts of METH during SA; however, female rats exhibit significant synaptic baseline differences when compared to males. Furthermore, females exhibited a significant increase in evoked excitatory currents. This increase in evoked glutamate was correlated with increases in NMDA currents and was not affected by application of a GluN2B selective blocker. We propose that METH SA selectively upregulates GluN2B-lacking NMDA receptors (NMDAR) in the PFC of female rats. Our results may provide a mechanistic explanation for the sex differences reported for METH addiction in females.

Cocaine-Induced Changes in Low-Dimensional Attractors of Local Field Potentials in Optogenetic Mice

Optogenetically evoked local field potential (LFP) recorded from the medial prefrontal cortex (mPFC) of mice during basal conditions and following a systemic cocaine administration were analyzed. Blue light stimuli were delivered to mPFC through a fiber optic every 2 s and each trial was repeated 100 times. As in the previous study, we used a surrogate data method to check that nonlinearity was present in the experimental LFPs and only used the last 1.5 s of steady activity to measure the LFPs phase resetting induced by the brief 10 ms light stimulus. We found that the steady dynamics of the mPFC in response to light stimuli could be reconstructed in a three-dimensional phase space with topologically similar "8"-shaped attractors across different animals. Therefore, cocaine did not change the complexity of the recorded nonlinear data compared to the control case. The phase space of the reconstructed attractor is determined by the LFP time series and its temporally shifted versions by a multiple of some lag time. We also compared the change in the attractor shape between cocaine-injected and control using (1) dendrogram clustering and (2) Frechet distance. We found about 20% overlap between control and cocaine trials when classified using dendrogram method, which suggest that it may be possible to describe mathematically both data sets with the same model and slightly different model parameters. We also found that the lag times are about three times shorter for cocaine trials compared to control. As a result, although the phase space trajectories for control and cocaine may look similar, their dynamics is significantly different.

Methamphetamine self-administration modulates glutamate neurophysiology

World-wide methamphetamine (meth) use is increasing at a rapid rate; therefore, it has become increasingly important to understand the synaptic changes and neural mechanisms affected by drug exposure. In rodents, 6-h access to contingent meth results in an escalation of drug intake and impaired cognitive sequelae typically associated with changes within the corticostriatal circuitry. There is a dearth of knowledge regarding the underlying physiological changes within this circuit following meth self-administration. We assessed pre- and postsynaptic changes in glutamate transmission in the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) following daily 6-h meth self-administration. In the mPFC, meth caused postsynaptic adaptations in ionotropic glutamate receptor distribution and function, expressed as a decrease in AMPA/NMDA ratio. This change was driven by an increase in NMDA receptor currents and an increase in GluN2B surface expression. In the NAc, meth decreased the paired-pulse ratio and increased the frequency of spontaneous excitatory postsynaptic currents with no indication of postsynaptic changes. These changes in mPFC synapses and NAc activity begin to characterize the impact of meth on the corticostriatal circuitry.

Effects of fingolimod administration in a genetic model of cognitive deficits

Notwithstanding recent advances, cognitive impairments are among the most difficult-to-treat symptoms in neuropsychiatric disorders. Deficits in information processing contributing to memory and sociability impairments are found across neuropsychiatric-related disorders. Previously, we have shown that mutations in the DTNBP1 gene (encoding dystrobrevin-binding protein 1 [dysbindin-1]) lead to abnormalities in synaptic glutamate release in the prefrontal cortex (PFC) and hippocampus and to cognitive deficits; glutamatergic transmission is important for cortical recurrent excitation that allows information processing in the PFC. To investigate possible means of restoring glutamate release and improving cognitive impairments, we assess the effects of increasing endogenous levels of brain-derived neurotrophic factor (BDNF) in a dysbindin-1-deficient mouse model. Increasing endogenous levels of BDNF may aid in remediating cognitive deficits, given the roles of BDNF in synaptic transmission, plasticity, and neuroprotection. To increase BDNF, we use a novel strategy, repeated intraperitoneal injections of fingolimod (Gilenya). Sphingolipids have recently been shown to have therapeutic value in several neurology-related disorders. Both wild-type (WT) and mutant (MUT) genotypes were tested for sociability and recognition memory, followed by measuring endogenous BDNF levels and presynaptic [Ca²⁺ ]_i within the PFC. Both genotypes were treated for 1 week with either saline or fingolimod. Relative to WT mice, MUT mice demonstrated impairments in sociability and recognition memory and lower presynaptic calcium. After fingolimod treatment, MUT mice exhibited significant improvements in sociability and recognition memory and increases in presynaptic calcium and endogenous concentrations of BDNF. These results show promise for counteracting the cognitive impairments seen in neuropsychiatric disorders and may shed light on the role of dysbindin-1. © 2016 Wiley Periodicals, Inc.

Low-dimensional attractor for neural activity from local field potentials in optogenetic mice

We used optogenetic mice to investigate possible nonlinear responses of the medial prefrontal cortex (mPFC) local network to light stimuli delivered by a 473 nm laser through a fiber optics. Every 2 s, a brief 10 ms light pulse was applied and the local field potentials (LFPs) were recorded with a 10 kHz sampling rate. The experiment was repeated 100 times and we only retained and analyzed data from six animals that showed stable and repeatable response to optical stimulations. The presence of nonlinearity in our data was checked using the null hypothesis that the data were linearly correlated in the temporal domain, but were random otherwise. For each trail, 100 surrogate data sets were generated and both time reversal asymmetry and false nearest neighbor (FNN) were used as discriminating statistics for the null hypothesis. We found that nonlinearity is present in all LFP data. The first 0.5 s of each 2 s LFP recording were dominated by the transient response of the networks. For each trial, we used the last 1.5 s of steady activity to measure the phase resetting induced by the brief 10 ms light stimulus. After correcting the LFPs for the effect of phase resetting, additional preprocessing was carried out using dendrograms to identify “similar” groups among LFP trials. We found that the steady dynamics of mPFC in response to light stimuli could be reconstructed in a three-dimensional phase space with topologically similar “8”-shaped attractors across different animals. Our results also open the possibility of designing a low-dimensional model for optical stimulation of the mPFC local network.

Optogenetically evoked gamma oscillations are disturbed by cocaine administration

Drugs of abuse have enormous societal impact by degrading the cognitive abilities, emotional state and social behavior of addicted individuals. Among other events involved in the addiction cycle, the study of a single exposure to cocaine, and the contribution of the effects of that event to the continuous and further use of drugs of abuse are fundamental. Gamma oscillations are thought to be important neural correlates of cognitive processing in the prefrontal cortex (PFC) which include decision making, set shifting and working memory. It follows that cocaine exposure might modulate gamma oscillations, which could result in reduced cognitive ability. Parvalbumin-positive fast-spiking interneurons play an orchestrating role in gamma oscillation induction and it has been shown recently that gamma oscillations can be induced in an anesthetized animal using optogenetic techniques. We use a knock-in mouse model together with optogenetics and in vivo electrophysiology to study the effects of acute cocaine on PFC gamma oscillation as a step toward understanding the cortical changes that may underlie continuous use of stimulants. Our results show that acute cocaine administration increases entrainment of the gamma oscillation to the optogentically induced driving frequency. Our results also suggest that this modulation of gamma oscillations is driven trough activation of D1 receptors. The acute cocaine-mediated changes in mPFC may underlie the enhancement of attention and awareness commonly reported by cocaine users and may contribute to the further use and abuse of psychostimulants.

Dysbindin-1 loss compromises NMDAR-dependent synaptic plasticity and contextual fear conditioning

Genetic variants in DTNBP1 encoding the protein dysbindin-1 have often been associated with schizophrenia and with the cognitive deficits prominent in that disorder. Because impaired function of the hippocampus is thought to play a role in these memory deficits and because NMDAR-dependent synaptic plasticity in this region is a proposed biological substrate for some hippocampal-dependent memory functions in schizophrenia, we hypothesized that reduced dysbindin-1 expression would lead to impairments in NMDAR-dependent synaptic plasticity and in contextual fear conditioning. Acute slices from male mice carrying 0, 1, or 2 null mutant alleles of the Dtnbp1 gene were prepared, and field recordings from the CA1 striatum radiatum were obtained before and after tetanization of Schaffer collaterals of CA3 pyramidal cells. Mice homozygous for the null mutation in Dtnbp1 exhibited significantly reduced NMDAR-dependent synaptic potentiation compared to wild type mice, an effect that could be rescued by bath application of the NMDA receptor coagonist glycine (10 μM). Behavioral testing in adult mice revealed deficits in hippocampal memory processes. Homozygous null mice exhibited lower conditional freezing, without a change in the response to shock itself, indicative of a learning and memory deficit. Taken together, these results indicate that a loss of dysbindin-1 impairs hippocampal plasticity which may, in part, explain the role dysbindin-1 plays in the cognitive impairments of schizophrenia.

Potential molecular mechanisms for decreased synaptic glutamate release in dysbindin-1 mutant mice

Behavioral genetic studies of humans have associated variation in the DTNBP1 gene with schizophrenia and its cognitive deficit phenotypes. The protein encoded by DTNBP1, dysbindin-1, is expressed in forebrain neurons where it interacts with proteins mediating vesicular trafficking and exocytosis. It has been shown that loss of dysbindin-1 results in a decrease in glutamate release in the prefrontal cortex; however the mechanisms underlying this decrease are not fully understood. In order to investigate this question, we evaluated dysbindin-1 null mutant mice, using electrophysiological recordings of prefrontal cortical neurons, imaging studies of vesicles, calcium dynamics and Western blot measures of synaptic proteins and Ca(2+) channels. Dysbindin-1 null mice showed a decrease in the ready releasable pool of synaptic vesicles, decreases in quantal size, decreases in the probability of release and deficits in the rate of endo- and exocytosis compared with wild-type controls. Moreover, the dysbindin-1 null mice show decreases in the [Ca(2+)]i,expression of L- and N-type Ca(2+)channels and several proteins involved in synaptic vesicle trafficking and priming. Our results provide new insights into the mechanisms of action of dysbindin-1.

Methamphetamine self-administration produces attentional set-shifting deficits and alters prefrontal cortical neurophysiology in rats

BACKGROUND

Chronic methamphetamine abusers exhibit deficits in tasks requiring intact prefrontal cortex function, and prefrontal cortex dysfunction has been implicated in the loss of control over drug use. This study used a combination of behavioral and electrophysiologic assessments in rats with a history of long access methamphetamine self-administration to determine methamphetamine-induced changes in prefrontal cortex-dependent attentional set-shifting performance, drug-seeking, and prefrontal cortex neuronal activity.

METHODS

Male Long-Evans rats self-administered methamphetamine (.02 mg/infusion, intravenous) or received yoked saline infusions for 6 hours a day for 14 days. Cognitive flexibility was assessed using an attentional set-shifting task before 2 weeks of self-administration and 1 day after self-administration. Animals then underwent 11 days of abstinence, followed by three subsequent tests for context-induced drug seeking. Finally, animals were anesthetized, and single-unit in vivo extracellular recordings were performed in the dorsomedial prefrontal cortex.

RESULTS

Methamphetamine-experienced rats showed escalated drug intake and context-induced drug-seeking following abstinence. During the extradimensional set-shift component, meth-experienced rats showed selective impairments that were identical to deficits produced by excitotoxic lesions of the prefrontal cortex. Rats with a history of chronic methamphetamine intake also exhibited higher basal firing frequency and a significantly greater proportion of burst-firing cells in the prefrontal cortex compared with yoked-saline controls.

CONCLUSIONS

Prefrontal cortex-specific alterations in neuronal function may play a key role in methamphetamine-induced attentional deficits and drug-seeking. These data support the possibility that targeting prefrontal cortex pathology may improve treatment outcome in methamphetamine addiction.

Reduced dysbindin expression mediates N-methyl-D-aspartate receptor hypofunction and impaired working memory performance

BACKGROUND

Schizophrenia is a heritable disorder associated with disrupted neural transmission and dysfunction of brain systems involved in higher cognition. The gene encoding dystrobrevin-binding-protein-1 (dysbindin) is a putative candidate gene associated with cognitive impairments, including memory deficits, in both schizophrenia patients and unaffected individuals. The underlying mechanism is thought to be based in changes in glutamatergic and dopaminergic function within the corticostriatal networks known to be critical for schizophrenia. This hypothesis derives support from studies of mice with a null mutation in the dysbindin gene that exhibit memory dysfunction and excitatory neurotransmission abnormalities in prefrontal and hippocampal networks. At a cellular level, dysbindin is thought to mediate presynaptic glutamatergic transmission.

METHODS

We investigated the relationship between glutamate receptor dynamics and memory performance in dysbindin mutant mice. We assessed N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor function in prefrontal cortex pyramidal neurons in vitro with whole-cell recordings, molecular quantitative analyses (reverse transcription-polymerase chain reaction) of the mandatory NMDA receptor subunit NR1, and cognitive function with a spatial working memory task.

RESULTS

Decreases in dysbindin are associated with specific decreases in NMDA-evoked currents in prefrontal pyramidal neurons, as well as decreases in NR1 expression. Furthermore, the degree of NR1 expression correlates with spatial working memory performance, providing a mechanistic explanation for cognitive changes previously associated with dysbindin expression.

CONCLUSIONS

These data show a significant downregulation of NMDA receptors due to dysbindin deficiency and illuminate molecular mechanisms mediating the association between dysbindin insufficiency and cognitive impairments associated with schizophrenia, encouraging study of the dysbindin/NR1 expression association in humans with schizophrenia.

Strong somatic stimulation differentially regulates the firing properties of prefrontal cortex neurons

Among the brain structures involved in processing affective stimuli, the roles of the prefrontal cortex (PFC) and the mesocorticolimbic dopaminergic (DA) innervation are well established. In contrast to our understanding of the reward stimuli, less is known about how strong somatic stimulation is processed within the PFC. Here, we examined the effects of a strong pinch delivered to the rat posterior paw on spontaneous and current-evoked activity of PFC neurons using intracellular recordings in anesthetized rats. Following the paw pinch, pyramidal cells exhibited a significant decrease in spontaneous activity along with a significant increase in the current-evoked firing. The increase in current-evoked firing elicited by the paw pinch was inversely correlated with the baseline firing rate. Systemic administration of a selective dopamine D2 receptor antagonist partially blocked the effects elicited by the paw pinch on cortical excitability, whereas systemic administration of a D1 antagonist seems to facilitate paw-mediated increases in evoked firing. These results suggest that strong somatic stimuli decrease spontaneous firing while increasing depolarization-evoked firing in a DA receptor dependent manner. These mechanisms may help in the control of the signal to noise ratio or the salience of information processing in the PFC following strong somatic stimulation.

Dysbindin modulates prefrontal cortical glutamatergic circuits and working memory function in mice

Behavioral genetic studies of humans have associated variation in the DTNBP1 gene with schizophrenia and its cognitive deficit phenotypes. The protein coded for by DTNBP1, dysbindin, is expressed within forebrain glutamatergic neurons, in which it interacts with proteins involved in vesicular trafficking and exocytosis. In order to further delineate the cellular, physiological, and behavioral phenotypes associated with reduced dysbindin expression, we conducted studies in mice carrying a null mutation within the dtnbp1 gene. Dysbindin mutants showed impairments of spatial working memory compared with wild-type controls; heterozygous mice showed intermediate levels of cognitive dysfunction. Deep-layer pyramidal neurons recorded in the prefrontal cortex of mutant mice showed reductions in paired-pulse facilitation, and evoked and miniature excitatory post-synaptic currents, indicating a difference in the function of pre-synaptic glutamatergic terminals as well as elevated spike thresholds. Taken together, these data indicate that dysbindin potently regulates excitatory transmission in the prefrontal cortex, potentially through a pre-synaptic mechanism, and consequently modulates cognitive functions depending on this brain region, providing new insights into the molecular mechanisms underlying cortical dysfunction in schizophrenia.

N-Acetylcysteine reverses cocaine-induced metaplasticity

Cocaine addiction is characterized by an impaired ability to develop adaptive behaviors that can compete with cocaine seeking, implying a deficit in the ability to induce plasticity in cortico-accumbens circuitry critical for regulating motivated behavior. RWe found that rats withdrawn from cocaine self-administration had a marked in vivo deficit in the ability to develop long-term potentation (LTP) and depression (LTD) in the nucleus accumbens core subregion following stimulation of prefrontal cortex. N-acetylcysteine treatment prevents relapse in animal models and craving in humans by activating cystine-glutamate exchange and thereby stimulating extrasynaptic metabotropic glutamate receptors (mGluR). N-acetylcysteine treatment restored the ability to induce LTP and LTD by indirectly stimulating mGluR2/3 and mGluR5, respectively. Cocaine self-administration induces metaplasticity that inhibits the further induction of synaptic plasticity, and this impairment can be reversed by N-acetylcysteine, a drug that also prevents relapse.

alpha2-Noradrenergic receptors activation enhances excitability and synaptic integration in rat prefrontal cortex pyramidal neurons via inhibition of HCN currents

Stimulation of alpha(2)-noradrenergic (NA) receptors within the PFC improves working memory performance. This improvement is accompanied by a selective increase in the activity of PFC neurons during delay periods, although the cellular mechanisms responsible for this enhanced response are largely unknown. Here we used current and voltage clamp recordings to characterize the response of layer V-VI PFC pyramidal neurons to alpha(2)-NA receptor stimulation. alpha(2)-NA receptor activation produced a small hyperpolarization of the resting membrane potential, which was accompanied by an increase in input resistance and evoked firing. Voltage clamp analysis demonstrated that alpha(2)-NA receptor stimulation inhibited a caesium and ZD7288-sensitive hyperpolarization-activated (HCN) inward current. Suppression of HCN current by alpha(2)-NA stimulation was not dependent on adenylate cyclase but instead required activation of a PLC-PKC linked signalling pathway. Similar to direct blockade of HCN channels, alpha(2)-NA receptor stimulation produced a significant enhancement in temporal summation during trains of distally evoked EPSPs. These dual effects of alpha(2)-NA receptor stimulation - membrane hyperpolarization and enhanced temporal integration - together produce an increase in the overall gain of the response of PFC pyramidal neurons to excitatory synaptic input. The net effect is the suppression of isolated excitatory inputs while enhancing the response to a coherent burst of synaptic activity.

The ability of the mesocortical dopamine system to operate in distinct temporal modes

BACKGROUND

This review discusses evidence that cells in the mesocortical dopamine (DA) system influence information processing in target areas across three distinct temporal domains.

DISCUSSIONS

Phasic bursting of midbrain DA neurons may provide temporally precise information about the mismatch between expected and actual rewards (prediction errors) that has been hypothesized to serve as a learning signal in efferent regions. However, because DA acts as a relatively slow modulator of cortical neurotransmission, it is unclear whether DA can indeed act to precisely transmit prediction errors to prefrontal cortex (PFC). In light of recent physiological and anatomical evidence, we propose that corelease of glutamate from DA and/or non-DA neurons in the VTA could serve to transmit this temporally precise signal. In contrast, DA acts in a protracted manner to provide spatially and temporally diffuse modulation of PFC pyramidal neurons and interneurons. This modulation occurs first via a relatively rapid depolarization of fast-spiking interneurons that acts on the order of seconds. This is followed by a more protracted modulation of a variety of other ionic currents on timescales of minutes to hours, which may bias the manner in which cortical networks process information. However, the prolonged actions of DA may be curtailed by counteracting influences, which likely include opposing actions at D1 and D2-like receptors that have been shown to be time- and concentration-dependent. In this way, the mesocortical DA system optimizes the characteristics of glutamate, GABA, and DA neurotransmission both within the midbrain and cortex to communicate temporally precise information and to modulate network activity patterns on prolonged timescales.

Long-term neuroadaptations produced by withdrawal from repeated cocaine treatment: role of dopaminergic receptors in modulating cortical excitability

Dopamine (DA) modulates neuronal activity in the prefrontal cortex (PFC) and is necessary for optimal cognitive function. Dopamine transmission in the PFC is also important for the behavioral adaptations produced by repeated exposure to cocaine. Therefore, we investigated the effects of repeated cocaine treatment followed by withdrawal (2-4 weeks) on the responsivity of cortical cells to electrical stimulation of the ventral tegmental area (VTA) and to systemic administration of DA D1 or D2 receptor antagonists. Cortical cells in cocaine- and saline-treated animals exhibited a similar decrease in excitability after the administration of D1 receptor antagonists. In contrast, cortical neurons from cocaine-treated rats exhibited a lack of D2-mediated regulation relative to saline rats. Furthermore, in contrast to saline-treated animals, VTA stimulation did not increase cortical excitability in the cocaine group. These data suggest that withdrawal from repeated cocaine administration elicits some long-term neuroadaptations in the PFC, including (1) reduced D2-mediated regulation of cortical excitability, (2) reduced responsivity of cortical cells to phasic increases in DA, and (3) a trend toward an overall decrease in excitability of PFC neurons.

Mesocortical dopamine neurons operate in distinct temporal domains using multimodal signaling

In vivo extracellular recording studies have traditionally shown that dopamine (DA) transiently inhibits prefrontal cortex (PFC) neurons, yet recent biophysical measurements in vitro indicate that DA enhances the evoked excitability of PFC neurons for prolonged periods. Moreover, although DA neurons apparently encode stimulus salience by transient alterations in firing, the temporal properties of the PFC DA signal associated with various behaviors is often extraordinarily prolonged. The present study used in vivo electrophysiological and electrochemical measures to show that the mesocortical system produces a fast non-DA-mediated postsynaptic response in the PFC that appears to be initiated by glutamate. In contrast, short burst stimulation of mesocortical DA neurons that produced transient (<4 s) DA release in the PFC caused a simultaneous reduction in spontaneous firing (consistent with extracellular in vivo recordings) and a form of DA-induced potentiation in which evoked firing was increased for tens of minutes (consistent with in vitro measurements). We suggest that the mesocortical system might transmit fast signals about reward or salience via corelease of glutamate, whereas the simultaneous prolonged DA-mediated modulation of firing biases the long-term processing dynamics of PFC networks.

Methylphenidate increases cortical excitability via activation of alpha-2 noradrenergic receptors

Although methylphenidate (MPH), a catecholaminergic reuptake blocker, is prescribed for attention-deficit/hyperactivity disorder, there is a dearth of information regarding the cellular basis of its actions. To address this issue, we used whole-cell patch-clamp recordings to investigate the roles of various catecholamine receptors in MPH-induced changes in cortical neuron excitability. We bath-applied dopamine or noradrenaline receptor antagonists in combination with MPH to pyramidal cells located in deep layers of the infralimbic and prelimbic prefrontal cortices. Application of MPH (10 microM) by itself increased cortical cell excitability in slices obtained from juvenile rats. This MPH-mediated increase in excitability was lost when catecholamines were depleted with reserpine prior to recording, demonstrating the requirement for a presynaptic monoamine component. Antagonist studies further revealed that stimulation of alpha-2 noradrenergic receptors mediates the MPH-induced increase in intrinsic excitability. Dopamine D1 receptors played no observable role in the actions of MPH. We therefore propose that MPH is acting to increase catecholaminergic tone in the PFC, and thereby increases cortical excitability by mediating the disinhibition of pyramidal cells through mechanisms that may include activation of alpha-2 adrenoreceptors located in interneurons.

Oceanographic conditions in North and Northwest Iberia and their influence on the Prestige oil spill

Oceanographic conditions at the time of the Prestige oil spill (November 2002) and following months are analyzed based on a set of hydrographic cruises. The ship sank off one of the flanks of the Galician Bank, an offshore seamount, and a major oil spill drifted to the N and NW Iberian coast mainly driven by dominant winds. Coastal circulation was characterized by freshwater plumes and the poleward slope current, and could have affected the fate of the oil spill and influenced stranding places. Seasonal evolution of oceanographic conditions in this particular year is compared with the long-term average and reveals specific features that need to be taken into account in studies of the impact of the oil spill on populations. Spring conditions commenced earlier than other years in the Southern Bay of Biscay, contrastingly in western Iberia. The lack of subsurface intrusion of subtropical waters suggests a low intense penetration of the poleward current in Spanish Biscay slopes. In western Iberia, the slope poleward current observed in late autumn weakens and is exported off slope during upwelling pulses in the spring, with no strong intrusion of the poleward current on the slope at the time of the spring bloom. A description of current velocities near the wreck on the Galician Bank is obtained after the analysis of a mooring line.

Prenatal disruption of neocortical development alters prefrontal cortical neuron responses to dopamine in adult rats

A growing body of evidence suggests that structural changes in the cortex may disrupt dopaminergic transmission in circuits involving the prefrontal cortex (PFC) and may contribute to the etiology of schizophrenia. In this study, we utilize a rodent model of neonatal disruption of cortical development using prenatal administration of the mitotoxin methylazoxymethanol acetate (MAM). Using intracellular recordings in vivo, we compare the physiology of prefrontal cortical neurons and their responses to topical administration of dopamine (DA) in intact animals and adult rats treated prenatally with MAM. Topical administration of DA hyperpolarized the membrane potential (MP) and decreased the firing rate of neurons recorded in deep layers of the PFC in intact animals. Furthermore, electrical stimulation of the VTA evoked fast onset epsps or long-lasting depolarizations in PFC neurons. In comparison, PFC neurons recorded in MAM-treated animals had significantly faster baseline firing rates. Moreover, topical administration of DA did not affect the MP or firing rate of the neurons in MAM-treated animals. However, MAM-treated animals exhibited an increase in the percentage of neurons responding with long-lasting depolarizations to stimulation of the VTA. The results of this study indicate that PFC neurons in the MAM-treated rats are not responsive to DA administered superficially, while at the same time exhibit greater responsiveness to VTA stimulation. These results are consistent with a rewiring of the corticolimbic system in response to neurodevelopmental insults.

Mechanisms underlying differential D1 versus D2 dopamine receptor regulation of inhibition in prefrontal cortex

Typically, D1 and D2 dopamine (DA) receptors exert opposing actions on intracellular signaling molecules and often have disparate physiological effects; however, the factors determining preferential activation of D1 versus D2 signaling are not clear. Here, in vitro patch-clamp recordings show that DA concentration is a critical determinant of D1 versus D2 signaling in prefrontal cortex (PFC). Low DA concentrations (<500 nm) enhance IPSCs via D1 receptors, protein kinase A, and cAMP. Higher DA concentrations (>1 microm) decrease IPSCs via the following cascade: D2-->G(i)-->platelet-derived growth factor receptor--> increase phospholipase C--> increase IP3--> increase Ca2+--> decrease dopamine and cAMP-regulated phosphoprotein-32--> increase protein phosphatase 1/2A--> decrease GABA(A). Blockade of any molecule in the D2-linked pathway reveals a D1-mediated increase in IPSCs, suggesting that D1 effects are occluded at higher DA concentrations by this D2-mediated pathway. Thus, DA concentration, by acting through separate signaling cascades, may determine the relative amount of cortical inhibition and thereby differentially regulate the tuning of cortical networks.

Acute cocaine administration depresses cortical activity

Psychostimulants, when administered acutely, produce significant deficits in cognitive tasks. Indeed, there is considerable evidence that acute administration of cocaine alters cellular processes at the level of the nucleus accumbens and the ventral tegmental area (VTA). However, there have been few studies that explore the acute effects of cocaine in the prefrontal cortex (PFC). Here we report that acute cocaine administration in vivo evokes a prolonged membrane depolarization, decreases cortical spontaneous firing, compromises spontaneous membrane bistability, and blunts the VTA-evoked responses in the PFC. Moreover, acute cocaine administration decreases the amplitude of the EPSP-IPSP sequence that precedes the initiation of the Up states in the PFC, therefore compromising the driving force of cortical bistability and thereby cortical excitability.

Synaptic basis of persistent activity in prefrontal cortex in vivo and in organotypic cultures

Persistent activity is observed in many cortical and subcortical brain regions, and may subserve a variety of functions. Within the prefrontal cortex (PFC), neurons transiently maintain information in working memory via persistent activity patterns; however, the mechanisms involved are largely unknown. The present study used intracellular recordings from deep layer PFC neurons in vivo and patch-clamp recordings from PFC neurons in organotypic brain slice cultures to examine the ionic mechanisms underlying persistent activity states evoked by various inputs. Persistent activity had consistent features regardless of the initiating stimulus; it was driven by non-NMDA glutamate receptors yet consisted of an initial GABA mediated component, followed by a prolonged synaptically mediated inward current that maintained the sustained depolarization on which rode many asynchronous GABA-mediated events. The stereotyped nature of the multiple-component persistent activity pattern reported here might be a common feature of interconnected cortical networks but within PFC could be related to the persistent activity required for working memory.

Repeated cocaine administration alters the electrophysiological properties of prefrontal cortical neurons

Recently it has become clear that some of the symptoms of addiction such as relapse to drug-taking behavior arise, in part, from a dysfunction in cognitive and emotional processing. This realization has promoted investigations into the physiology and pathophysiology of forebrain circuits that are both innervated by dopamine and play an important role in cognitive processing, including the prefrontal cortex. In order to study long-term neuroadaptations occurring in the prefrontal cortex of the rat as a consequence of psychostimulant administration, cocaine was repeatedly administered in either a contingent or a non-contingent manner. At least 2 weeks following the last cocaine injection, in vivo intracellular recordings were made from neurons located in the deep layers of the prefrontal cortex. Repeated cocaine administration abolished the presence of membrane bistability normally present in neurons located in the limbic prefrontal cortex. These results indicate that repeated exposure to cocaine produces enduring changes in the basal activity of neurons in the prefrontal cortex that may contribute to previously identify cognitive and emotional dysfunctions in cocaine addicts.

Stimulation of D1-type dopamine receptors enhances excitability in prefrontal cortical pyramidal neurons in a state-dependent manner

Prefrontal cortex neurons recorded in vivo exhibit bistable activity states, consisting of a depolarized phase (-55mV) and a hyperpolarized phase (-85mV). These "up" and "down" states have durations ranging from 800ms to 1s and a periodicity of approximately 1Hz. This study examines the state-dependency of prefrontal cortical neuron responses to dopamine, in which the bistable-state was approximated in vitro by intracellular current injection. At resting membrane potential (n=10), dopamine caused a significant depolarization of the membrane potential without altering any of the other electrophysiological characteristics tested. In contrast, both dopamine (30 microM, 5min) and the D1 receptor agonist SKF 38393 (5 and 10 microM) increased cell excitability when the cell was in the depolarized state (i.e., -55mV) but not the hyperpolarized state (i.e., -85 mV; n=10). This increase in excitability was accompanied by a decrease in the rheobase current. The SKF 38393-enhanced excitability was dose-dependent and could be blocked by bath administration of the D1 receptor antagonist SCH 23390 (5 and 10 microM). Administration of the GABA antagonist bicuculline (7 microM) plus the N-methyl-D-aspartate channel blocker CPP (10 microM) produced an additional increase in the excitability of prefrontal cortex neurons that was not dependent on the membrane potential. From these data we suggest that dopamine exerts state-dependent modulatory effects on the excitability of neurons in deep layers of the prefrontal cortex.

Regulation of limbic information outflow by the subthalamic nucleus: excitatory amino acid projections to the ventral pallidum

The subthalamic nucleus (STN), a component of the basal ganglia motor system, sends an excitatory amino acid (EAA)-containing projection to the ventral pallidum (VP), a major limbic system output region. The VP contains both NMDA and AMPA subtypes of EAA receptors. To characterize the physiology of the subthalamic pathway to the VP, and to determine the influence of EAA receptor subtypes, in vivo intracellular recordings, and in vivo extracellular recordings combined with microiontophoresis, were made from VP neurons in anesthetized rats. Of the intracellularly recorded neurons, 86% responded to STN stimulation, and these displayed EPSPs with an onset of 8.7 msec, consistent with a monosynaptic input. The EPSPs evoked in spontaneously firing neurons were nearly twice the amplitude of those in nonfiring cells (13.1 vs 6.8 mV, respectively). As neurons were depolarized by current injection, the latency for spiking decreased from 24.2 to 14.2 msec, although EPSP latency was unaffected. Eighty-seven percent of the extracellularly recorded VP neurons responded to STN stimulation with a rapid and robust enhancement of spiking; the response onset, like the EPSP onset, equaled 8.7 msec. Firing rate was enhanced by NMDA in 94% of the STN-excited cells, and AMPA increased firing in 94% as well. The NMDA-selective antagonist AP-5 attenuated 67% of the STN-evoked excitatory responses, and the AMPA-selective antagonist CNQX attenuated 52%. Both antagonists attenuated 33% of responses, and 78% were attenuated by at least one. This evidence suggests that a great majority of VP neurons are directly influenced by STN activation and that both NMDA and non-NMDA receptors are involved. Moreover, the VP response to STN stimulation appears to be strongly dependent on the depolarization state of the neuron.

American Academy of Pediatrics. Committee on Child Abuse and Neglect and Committee on Community Health Services. Investigation and review of unexpected infant and child deaths

Although there is a continuing need for timely review of child deaths, no uniform system exists for investigation in the United States. Investigation of a death that is traumatic, unexpected, obscure, suspicious, or otherwise unexplained in a child younger than 18 years requires a scene investigation and an autopsy. Review of these deaths requires the participation of pediatricians and other professionals, usually as a child death review team. An appropriately constituted team should evaluate the death investigation process, review difficult cases, and compile child death statistics.

Dopamine modulates the responsivity of mediodorsal thalamic cells recorded in vitro

The mediodorsal thalamic nucleus (MD) receives convergent inputs from subcortical limbic structures that overlap with a dopaminergic (DA) innervation. In this study, we describe the effects of DA agonists on the basal and evoked electrophysiological activity of identified thalamic cells of rats recorded in vitro. Administration of the D1 agonist SFK 38393 (10 microM) did not produce a clear effect on the physiological properties of the thalamic cells recorded. In contrast, bath administration of the D2 agonist quinpirole (10 microM) resulted in an enhancement of membrane excitability, facilitation of the occurrence of low-threshold spikes (LTSs), and changes in the resting membrane potential of the thalamic cells tested. The quinpirole-mediated responses were reversed by administration of the D2 antagonist haloperidol. Results from experiments performed with different [K+] and K+ channel blockers suggest that the effects of quinpirole are mediated at least in part by changes in K+ conductances. The results from this study suggest that DA can modulate the excitability of thalamic cells and in turn may influence the way that the thalamocortical system integrates information.

Response of the ventral pallidal/mediodorsal thalamic system to antipsychotic drug administration: involvement of the prefrontal cortex

Intracellular recordings were obtained from rat ventral pallidal (VP) and mediodorsal thalamic (MD) cells in vivo and the effects of antipsychotic drugs on their basal and evoked electrophysiological characteristics were assessed. Administration of either haloperidol or clozapine caused a significant decrease in the average firing rate, accompanied by a hyperpolarization of the membrane potential in the VP cells recorded. However, neither drug induced a substantial change in the other basic membrane properties of the MD cells or VP cells tested. In addition, in 50% of the MD cells tested, both antipsychotic drugs caused a change in spike discharge from an oscillatory pattern to a tonic discharge mode. In rats that had received ibotenic acid lesions of the prefrontal cortex (PFCtx) 4-8 weeks prior to recording, cells in the VP exhibited similar changes in firing frequency in response to haloperidol administration as those in the intact rats. However, in contrast to the intact rats, MD cells recorded from rats with PFCtx lesions exhibited a significant increase in firing rate after haloperidol administration. The results from this study suggest that the prefrontal cortex plays a role in modulating the response of the thalamus to antipsychotic drugs.

Computer reminders improve on-time immunization rates

OBJECTIVES

This study examines the effectiveness of computer-generated telephone reminders in improving infants receiving on-time immunizations. A computer called parents at home, reminded them of their child's visit, and asked if they could keep the appointment. If parents either canceled or failed to honor the appointment, the computer called back a few days later and asked them to reschedule.

METHODS

A medical assistant recruited 124 consecutive mothers to receive automated computer reminders. These mothers' infants were younger than 6 months, were being seen at an outpatient clinic for a first visit, and were patients of three attending physicians and three nurse practitioners. These infants were compared to 89 infants from the same clinic, in the same age range, who were being seen for the first time during the same period by the same providers but not contacted by the medical assistant. Subjects were selected from mothers who brought their infants for their first visit in an outpatient urban clinic that serves predominantly minority clients. A research assistant reviewed patients' medical records and collected the infants' birthday, mothers' age, race, source of payments, and the immunization record of the infants. Immunization was considered to be late if, at the time of the first visit, it was more than 30 days past due for any of the recommended immunizations of the American Academy of Pediatrics, except for Hepatitis B vaccine which was not recommended at the time of the study. The dependent variable was on-time immunization. The independent variables were age of the mother at baseline, age of the child at baseline, and membership in either the comparison or the experimental group. Chi-square tests and logistic regression were used to analyze the data.

RESULTS

The participation rate for appointments for the experimental group was 82%, as compared to a 69% overall participation rate for the clinic providers. The on-time immunization rate for experimental subjects was 67.8%, whereas the comparison group had an on-time immunization rate of 43.4% (differences were significant at alpha levels less than 0.01).

CONCLUSIONS

Computerized reminders sent to the parents led to an increase in participation rate at the clinic and an increase in on-time immunization for their infants.

Physiological properties of rat ventral pallidal neurons recorded intracellularly in vivo

1. The physiology of ventral pallidal (VP) cells was investigated using in vivo intracellular recording and staining techniques in adult rats. Based on electrophysiological criteria, three different types of cells were found: type A cells, which fired phasic spikes that did not exhibit a substantial afterhyperpolarization (AHP), type B cells, which exhibited a slow ramplike depolarization that preceded the short-duration action potential; the spike was followed by a prominent AHP, and type C cells, which were the only cells that fired spikes in couplets or bursts, with the spikes in a burst exhibiting a progressive increase in duration and a decrease in amplitude. These cells also exhibited a rebound low threshold spikelike event. Furthermore, 18% of the VP cells recorded exhibited a slow subthreshold oscillation of the membrane potential (< 1 Hz). 2. The response of VP cells to stimulation of fibers arising from the prefrontal cortex, nucleus accumbens, and mediodorsal thalamic nucleus (MD) was examined. In contrast to our initial predictions, all cells responded to nucleus accumbens stimulation with excitation. Type A and B cells responded to nucleus accumbens stimulation with excitation and to MD stimulation with antidromic-like responses, orthodromic excitation, or evoked inhibitory postsynaptic potentials. Only type A cells responded to prefrontal cortical stimulation. Type C cells only responded to stimulation of the nucleus accumbens, which resulted in evoked excitatory postsynaptic potentials. 3. The cells in the VP therefore can be segregated into three physiologically defined groups according to action potential discharge patterns and their response to afferent fiber stimulation.

A survey of pediatric management of dyslipidemias in New England

We recently surveyed physicians attending the New England Pediatric Preventive Cardiology Society. Sixteen physicians who actively evaluated children with dyslipidemia completed questionnaires; at least one representative from six of the seven medical schools in New England was included. The survey elicited responses to five hypothetical cases of childhood dyslipidemia which were representative of the types of lipid problems commonly referred to pediatric lipid specialists. Diet modification was the initial treatment of choice of all participants. For any set of lipid values, postpubertal age increased the proportion of respondents who would have prescribed medication. When pharmacologic intervention was elected, resin binders (cholestyramine or cholestipol) and niacin were most commonly prescribed. The responses of the physicians showed considerable variation in the threshold for beginning medications. In summary, this survey suggests substantial variation in the approach to pharmacologic management of pediatric dyslipidemias in the New England region.