Sox1-deficient mice suffer from epilepsy associated with abnormal ventral forebrain development and olfactory cortex hyperexcitability

Mutations in several classes of embryonically-expressed transcription factor genes are associated with behavioral disorders and epilepsies. However, there is little known about how such genetic and neurodevelopmental defects lead to brain dysfunction. Here we present the characterization of an epilepsy syndrome caused by the absence of the transcription factor SOX1 in mice. In vivo electroencephalographic recordings from SOX1 mutants established a correlation between behavioral changes and cortical output that was consistent with a seizure origin in the limbic forebrain. In vitro intracellular recordings from three major forebrain regions, neocortex, hippocampus and olfactory (piriform) cortex (OC) showed that only the OC exhibits abnormal enhanced synaptic excitability and spontaneous epileptiform discharges. Furthermore, the hyperexcitability of the OC neurons was present in mutants prior to the onset of seizures but was completely absent from both the hippocampus and neocortex of the same animals. The local inhibitory GABAergic neurotransmission remained normal in the OC of SOX1-deficient brains, but there was a severe developmental deficit of OC postsynaptic target neurons, mainly GABAergic projection neurons within the olfactory tubercle and the nucleus accumbens shell. Our data show that SOX1 is essential for ventral telencephalic development and suggest that the neurodevelopmental defect disrupts local neuronal circuits leading to epilepsy in the SOX1-deficient mice

Cholinergic modulation of intrinsic fibre-evoked excitatory transmission contains a nicotinic component in immature but not adult rat piriform cortex, in vitro

The piriform cortex (PC) is highly prone to epileptogenesis, particularly in immature animals, where decreased muscarinic modulation of PC intrinsic fibre excitatory neurotransmission is implicated as a likely cause. However, whether higher levels of acetylcholine (ACh) release occur in immature vs. adult PC remains unclear. We investigated this using in vitro extracellular electrophysiological recording techniques. Intrinsic fibre-evoked extracellular field potentials (EFPs) were recorded from layers II to III in PC brain slices prepared from immature (P14-18) and adult (P>40) rats. Adult and immature PC EFPs were suppressed by eserine (1muM) or neostigmine (1muM) application, with a greater suppression in immature ( approximately 40%) than adult ( approximately 30%) slices. Subsequent application of atropine (1muM) reversed EFP suppression, producing supranormal ( approximately 12%) recovery in adult slices, suggesting that suppression was solely muscarinic ACh receptor-mediated and that some 'basal' cholinergic 'tone' was present. Conversely, atropine only partially reversed anticholinesterase effects in immature slices, suggesting the presence of additional non-muscarinic modulation. Accordingly, nicotine (50muM) caused immature field suppression ( approximately 30%) that was further enhanced by neostigmine, whereas it had no effect on adult EFPs. Unlike atropine, nicotinic antagonists, mecamylamine and methyllycaconitine, induced immature supranormal field recovery ( approximately 20%) following anticholinesterase-induced suppression (with no effect on adult slices), confirming that basal cholinergic 'tone' was also present. We suggest that nicotinic inhibitory cholinergic modulation occurs in the immature rat PC intrinsic excitatory fibre system, possibly to complement the existing, weak muscarinic modulation, and could be another important developmentally regulated system governing immature PC susceptibility towards epileptogenesis.

Developmental changes in presynaptic muscarinic modulation of excitatory and inhibitory neurotransmission in rat piriform cortex in vitro: relevance to epileptiform bursting susceptibility

Suppression of depolarizing postsynaptic potentials and isolated GABA-A receptor-mediated fast inhibitory postsynaptic potentials by the muscarinic acetylcholine receptor agonist, oxotremorine-M (10 microM), was investigated in adult and immature (P14-P30) rat piriform cortical (PC) slices using intracellular recording. Depolarizing postsynaptic potentials evoked by layers II-III stimulation underwent concentration-dependent inhibition in oxotremorine-M that was most likely presynaptic and M2 muscarinic acetylcholine receptor-mediated in immature, but M1-mediated in adult (P40-P80) slices; percentage inhibition was smaller in immature than in adult piriform cortex. In contrast, compared with adults, layer Ia-evoked depolarizing postsynaptic potentials in immature piriform cortex slices in oxotremorine-M, showed a prolonged multiphasic depolarization with superimposed fast transients and spikes, and an increased 'all-or-nothing' character. Isolated N-methyl-d-aspartate receptor-mediated layer Ia depolarizing postsynaptic potentials (although significantly larger in immature slices) were however, unaffected by oxotremorine-M, but blocked by dl-2-amino-5-phosphonovaleric acid. Fast inhibitory postsynaptic potentials evoked by layer Ib or layers II-III-fiber stimulation in immature slices were significantly smaller than in adults, despite similar estimated mean reversal potentials ( approximately -69 and -70 mV respectively). In oxotremorine-M, only layer Ib-fast inhibitory postsynaptic potentials were suppressed; suppression was again most likely presynaptic M2-mediated in immature slices, but M1-mediated in adults. The degree of fast inhibitory postsynaptic potential suppression was however, greater in immature than in adult piriform cortex. Our results demonstrate some important physiological and pharmacological differences between excitatory and inhibitory synaptic systems in adult and immature piriform cortex that could contribute toward the increased susceptibility of this region to muscarinic agonist-induced epileptiform activity in immature brain slices.

A novel component of cannabis extract potentiates excitatory synaptic transmission in rat olfactory cortex in vitro

Cannabis is a potential treatment for epilepsy, although the few human studies supporting this use have proved inconclusive. Previously, we showed that a standardized cannabis extract (SCE), isolated Delta(9)-tetrahydrocannabinol (Delta(9)-THC), and even Delta(9)-THC-free SCE inhibited muscarinic agonist-induced epileptiform bursting in rat olfactory cortical brain slices, acting via CB1 receptors. The present work demonstrates that although Delta(9)-THC (1microM) significantly depressed evoked depolarizing postsynaptic potentials (PSPs) in rat olfactory cortex neurones, both SCE and Delta(9)-THC-free SCE significantly potentiated evoked PSPs (all results were fully reversed by the CB1 receptor antagonist SR141716A, 1microM); interestingly, the potentiation by Delta(9)-THC-free SCE was greater than that produced by SCE. On comparing the effects of Delta(9)-THC-free SCE upon evoked PSPs and artificial PSPs (aPSPs; evoked electrotonically following brief intracellular current injection), PSPs were enhanced, whereas aPSPs were unaffected, suggesting that the effect was not due to changes in background input resistance. Similar recordings made using CB1 receptor-deficient knockout mice (CB1(-/-)) and wild-type littermate controls revealed cannabinoid or extract-induced changes in membrane resistance, cell excitability and synaptic transmission in wild-type mice that were similar to those seen in rat neurones, but no effect on these properties were seen in CB1(-/-) cells. It appears that the unknown extract constituent(s) effects over-rode the suppressive effects of Delta(9)-THC on excitatory neurotransmitter release, which may explain some patients' preference for herbal cannabis rather than isolated Delta(9)-THC (due to attenuation of some of the central Delta(9)-THC side effects) and possibly account for the rare incidence of seizures in some individuals taking cannabis recreationally

Inverse amygdala and medial prefrontal cortex responses to surprised faces

Here we show inverse fMRI activation patterns in amygdala and medial prefrontal cortex (mPFC) depending upon whether subjects interpreted surprised facial expressions positively or negatively. More negative interpretations of surprised faces were associated with greater signal changes in the right ventral amygdala, while more positive interpretations were associated with greater signal changes in the ventral mPFC. Accordingly, signal change within these two areas was inversely correlated. Thus, individual differences in the judgment of surprised faces are related to a systematic inverse relationship between amygdala and mPFC activity, a circuitry that the animal literature suggests is critical to the assessment of stimuli that predict potential positive vs negative outcomes.

Amygdala and ventromedial prefrontal cortex are inversely coupled during regulation of negative affect and predict the diurnal pattern of cortisol secretion among older adults

Among younger adults, the ability to willfully regulate negative affect, enabling effective responses to stressful experiences, engages regions of prefrontal cortex (PFC) and the amygdala. Because regions of PFC and the amygdala are known to influence the hypothalamic-pituitary-adrenal axis, here we test whether PFC and amygdala responses during emotion regulation predict the diurnal pattern of salivary cortisol secretion. We also test whether PFC and amygdala regions are engaged during emotion regulation in older (62- to 64-year-old) rather than younger individuals. We measured brain activity using functional magnetic resonance imaging as participants regulated (increased or decreased) their affective responses or attended to negative picture stimuli. We also collected saliva samples for 1 week at home for cortisol assay. Consistent with previous work in younger samples, increasing negative affect resulted in ventral lateral, dorsolateral, and dorsomedial regions of PFC and amygdala activation. In contrast to previous work, decreasing negative affect did not produce the predicted robust pattern of higher PFC and lower amygdala activation. Individuals demonstrating the predicted effect (decrease s attend in the amygdala), however, exhibited higher signal in ventromedial prefrontal cortex (VMPFC) for the same contrast. Furthermore, participants displaying higher VMPFC and lower amygdala signal when decreasing compared with the attention control condition evidenced steeper, more normative declines in cortisol over the course of the day. Individual differences yielded the predicted link between brain function while reducing negative affect in the laboratory and diurnal regulation of endocrine activity in the home environment.

Anticholinesterase-induced epileptiform activity in immature rat piriform cortex slices, in vitro

Purpose: Acute in vitro brain slice models are commonly used to study epileptiform seizure generation and to test anti-epileptic drug action. Seizure-like activity can be readily induced by manipulating external ionic concentrations or by adding convulsant agents to the bathing medium. We previously showed that epileptiform bursting was induced in slices of immature (P14–28) rat piriform cortex (PC) by applying oxotremorine-M, a potent muscarinic receptor agonist. Here, we examined whether raising levels of endogenous acetylcholine (ACh) by exposure to anticholinesterases, could also induce epileptiform events in immature (P12–14) or early postnatal (P7–9) rat PC brain slices. Methods: The effects of anticholinesterases were investigated in rat PC neurons using both extracellular MEA (P7–9 slices) and intracellular (P12–14 slices) recording methods. Results: In P7–9 slices, eserine (20 μM) or neostigmine (20 μM) induced low amplitude, low frequency bursting activity in all three PC cell layers (I–III), particularly layer III, where neuronal muscarinic responsiveness is known to predominate. In P12–14 neurons, neostigmine produced a slow depolarization together with an increase in input resistance and evoked cell firing. Depolarizing postsynaptic potentials evoked by intrinsic fibre stimulation were selectively depressed although spontaneous bursting was not observed. Neostigmine effects were blocked by atropine (1 μM), confirming their muscarinic nature. We conclude that elevation of endogenous ACh by anticholinesterases can induce bursting in early postnatal PC brain slices, further highlighting the epileptogenic capacity of this brain region. However, this tendency declines with further development, possibly as local inhibitory circuit mechanisms become more dominant.

Shared neural circuits for mentalizing about the self and others

Although many examples exist for shared neural representations of self and other, it is unknown how such shared representations interact with the rest of the brain. Furthermore, do high-level inference-based shared mentalizing representations interact with lower level embodied/simulation-based shared representations? We used functional neuroimaging (fMRI) and a functional connectivity approach to assess these questions during high-level inference-based mentalizing. Shared mentalizing representations in ventromedial prefrontal cortex, posterior cingulate/precuneus, and temporo-parietal junction (TPJ) all exhibited identical functional connectivity patterns during mentalizing of both self and other. Connectivity patterns were distributed across low-level embodied neural systems such as the frontal operculum/ventral premotor cortex, the anterior insula, the primary sensorimotor cortex, and the presupplementary motor area. These results demonstrate that identical neural circuits are implementing processes involved in mentalizing of both self and other and that the nature of such processes may be the integration of low-level embodied processes within higher level inference-based mentalizing.

Proteomic analysis of plasma membrane vesicles isolated from the rat renal cortex

Polarized epithelial cells are responsible for the vectorial transport of solutes and have a key role in maintaining body fluid and electrolyte homeostasis. Such cells contain structurally and functionally distinct plasma membrane domains. Brush border and basolateral membranes of renal and intestinal epithelial cells can be separated using a number of different separation techniques, which allow their different transport functions and receptor expressions to be studied. In this communication, we report a proteomic analysis of these two membrane segments, apical and basolateral, obtained from the rat renal cortex isolated by two different methods: differential centrifugation and free-flow electrophoresis. The study was aimed at assessing the nature of the major proteins isolated by these two separation techniques. Two analytical strategies were used: separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) at the protein level or by cation-exchange high-performance liquid chromatography (HPLC) after proteolysis (i.e., at the peptide level). Proteolytic peptides derived from the proteins present in gel pieces or from HPLC fractions after proteolysis were sequenced by on-line liquid chromatography-tandem mass spectrometry (LC-MS/MS). Several hundred proteins were identified in each membrane section. In addition to proteins known to be located at the apical and basolateral membranes, several novel proteins were also identified. In particular, a number of proteins with putative roles in signal transduction were identified in both membranes. To our knowledge, this is the first reported study to try and characterize the membrane proteome of polarized epithelial cells and to provide a data set of the most abundant proteins present in renal proximal tubule cell membranes.

Proteomic analysis of plasma membrane vesicles isolated from the rat renal cortex

Polarized epithelial cells are responsible for the vectorial transport of solutes and have a key role in maintaining body fluid and electrolyte homeostasis. Such cells contain structurally and functionally distinct plasma membrane domains. Brush border and basolateral membranes of renal and intestinal epithelial cells can be separated using a number of different separation techniques, which allow their different transport functions and receptor expressions to be studied. In this communication, we report a proteomic analysis of these two membrane segments, apical and basolateral, obtained from the rat renal cortex isolated by two different methods: differential centrifugation and free-flow electrophoresis. The study was aimed at assessing the nature of the major proteins isolated by these two separation techniques. Two analytical strategies were used: separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) at the protein level or by cation-exchange high-performance liquid chromatography (HPLC) after proteolysis (i.e., at the peptide level). Proteolytic peptides derived from the proteins present in gel pieces or from HPLC fractions after proteolysis were sequenced by on-line liquid chromatography-tandem mass spectrometry (LC-MS/MS). Several hundred proteins were identified in each membrane section. In addition to proteins known to be located at the apical and basolateral membranes, several novel proteins were also identified. In particular, a number of proteins with putative roles in signal transduction were identified in both membranes. To our knowledge, this is the first reported study to try and characterize the membrane proteome of polarized epithelial cells and to provide a data set of the most abundant proteins present in renal proximal tubule cell membranes.

Microglial activation correlates with severity in Huntington disease: a clinical and PET study

Background: Huntington disease ( HD) is characterized by the progressive death of medium spiny dopamine receptor bearing striatal GABAergic neurons. In addition, microglial activation in the areas of neuronal loss has recently been described in postmortem studies. Activated microglia are known to release neurotoxic cytokines, and these may contribute to the pathologic process. Methods: To evaluate in vivo the involvement of microglia activation in HD, the authors studied patients at different stages of the disease using [ C-11]( R)-PK11195 PET, a marker of microglia activation, and [ C-11] raclopride PET, a marker of dopamine D2 receptor binding and hence striatal GABAergic cell function. Results: In HD patients, a significant increase in striatal [ C-11]( R)-PK11195 binding was observed, which significantly correlated with disease severity as reflected by the striatal reduction in [ C-11] raclopride binding, the Unified Huntington's Disease Rating Scale score, and the patients' CAG index. Also detected were significant increases in microglia activation in cortical regions including prefrontal cortex and anterior cingulate. Conclusions: These [ C-11]( R)-PK11195 PET findings show that the level of microglial activation correlates with Huntington disease ( HD) severity. They lend support to the view that microglia contribute to the ongoing neuronal degeneration in HD and indicate that [ C-11]( R)-PK11195 PET provides a valuable marker when monitoring the efficacy of putative neuroprotecting agents in this relentlessly progressive genetic disorder.

The BOLD response during Stroop task-like inhibition paradigms: effects of task difficulty and task-relevant modality

Previous studies of the Stroop task propose two key mediators: the prefrontal and cingulate cortices but hints exist of functional specialization within these regions. This study aimed to examine the effect of task modality upon the prefrontal and cingulate response by examining the response to colour, number, and shape Stroop tasks whilst BOLD fMRI images were acquired on a Siemens 3 T MRI scanner. Behavioural analyses indicated facilitation and interference effects and a noticeable effect of task difficulty. Some modular effects of modality were observed in the prefrontal cortex that survived exclusion of task difficulty related activations. No effect of task-relevant information was observed in the anterior cingulate. Future comparisons of the mediation of selective attention need to consider the effects of task context and task difficulty. (c) 2005 Elsevier Inc. All rights reserved.

Freeze-frame: a new infant inhibition task and its relation to frontal cortex tasks during infancy and early childhood

The current study investigated a new, easily administered, visual inhibition task for infants termed the Freeze-Frame task. In the new task, 9-month-olds were encouraged to inhibit looks to peripheral distractors. This was done by briefly freezing a central animated stimulus when infants looked to the distractors. Half of the trials presented an engaging central stimulus, and the other half presented a repetitive central stimulus. Three measures of inhibitory function were derived from the task and compared with performance on a set of frontal cortex tasks administered at 9 and 24 months of age. As expected, infants' ability to learn to selectively inhibit looks to the distractors at 9 months predicted performance at 24 months. However, performance differences in the two Freeze-Frame trial types early in the experiment also turned out to be an important predictor. The results are discussed in terms of the validity of the Freeze-Frame task as an early measure of different components of inhibitory function. (C) 2007 Elsevier Inc. All rights reserved.

Objects and positions in visual scenes: effects of perirhinal and postrhinal cortex lesions in the rat

The authors assessed rats' encoding of the appearance or egocentric position of objects within visual scenes containing 3 objects (Experiment 1) or I object (Experiment 2A). Experiment 2B assessed encoding of the shape and fill pattern of single objects, and encoding of configurations (object + position, shape + fill). All were assessed by testing rats' ability to discriminate changes from familiar scenes (constant-negative paradigm). Perirhinal cortex lesions impaired encoding of objects and their shape; postrhinal cortex lesions impaired encoding of egocentric position, but the effect may have been partly due to entorhinal involvement. Neither lesioned group was impaired in detecting configural change. In Experiment 1, both lesion groups were impaired in detecting small changes in relative position of the 3 objects, suggesting that more sensitive tests might reveal configural encoding deficits.

Learning associations between places and visual cues without learning to navigate: neither fornix nor entorhinal cortex is required

Rats with fornix transection, or with cytotoxic retrohippocampal lesions that removed entorhinal cortex plus ventral subiculum, performed a task that permits incidental learning about either allocentric (Allo) or egocentric (Ego) spatial cues without the need to navigate by them. Rats learned eight visual discriminations among computer-displayed scenes in a Y-maze, using the constant-negative paradigm. Every discrimination problem included two familiar scenes (constants) and many less familiar scenes (variables). On each trial, the rats chose between a constant and a variable scene, with the choice of the variable rewarded. In six problems, the two constant scenes had correlated spatial properties, either Alto (each constant appeared always in the same maze arm) or Ego (each constant always appeared in a fixed direction from the start arm) or both (Allo + Ego). In two No-Cue (NC) problems, the two constants appeared in randomly determined arms and directions. Intact rats learn problems with an added Allo or Ego cue faster than NC problems; this facilitation provides indirect evidence that they learn the associations between scenes and spatial cues, even though that is not required for problem solution. Fornix and retrohippocampal-lesioned groups learned NC problems at a similar rate to sham-operated controls and showed as much facilitation of learning by added spatial cues as did the controls; therefore, both lesion groups must have encoded the spatial cues and have incidentally learned their associations with particular constant scenes. Similar facilitation was seen in subgroups that had short or long prior experience with the apparatus and task. Therefore, neither major hippocampal input-output system is crucial for learning about allocentric or egocentric cues in this paradigm, which does not require rats to control their choices or navigation directly by spatial cues.