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.