Neurotransmitters in the cerebral cortex

Loss of intracellular FGF14 (iFGF14) increases excitability of mature hippocampal pyramidal neurons

Mutations in FGF14, which encodes intracellular fibroblast growth factor 14 (iFGF14), have been linked to spinocerebellar ataxia type 27 (SCA27), a multisystem disorder associated with deficits in motor coordination and cognitive function. Mice lacking iFGF14 (Fgf14-/-) display similar phenotypes, and we have previously shown that the deficits in motor coordination reflect reduced excitability of cerebellar Purkinje neurons, owing to a hyperpolarizing shift in the voltage-dependence of voltage-gated Na+ (Nav) current steady-state inactivation. Here, we present the results of experiments designed to test the hypothesis that loss of iFGF14 also attenuates the intrinsic excitability of mature hippocampal pyramidal neurons. Current-clamp recordings from CA1 pyramidal neurons in acute in vitro slices, however, revealed that evoked repetitive firing rates were higher in Fgf14-/- than in wild type (WT) cells. Also, in contrast with Purkinje neurons, voltage-clamp recordings demonstrated that the loss of iFGF14 did not affect the voltage dependence of steady-state inactivation of the Nav currents in CA1 pyramidal neurons. In addition, in contrast with results reported for neonatal (rat) hippocampal pyramidal neurons in dissociated cell culture, immunohistochemical experiments revealed that loss of iFGF14 does not disrupt the localization or alter the normalized distribution of α-Nav1.6 or α-ankyrin G labeling along the axon initial segments (AIS) of mature hippocampal CA1 neurons in situ. However, the integrated intensities of α-Nav1.6 labeling were significantly higher along the AIS of Fgf14-/-, compared with WT, adult hippocampal CA1 pyramidal neurons, consistent with the marked increase in the excitability of CA1 neurons with the loss of iFGF14.

Loss of Intracellular Fibroblast Growth Factor 14 (iFGF14) Increases the Excitability of Mature Hippocampal and Cortical Pyramidal Neurons

Mutations in FGF14 , which encodes intracellular fibroblast growth factor 14 (iFGF14), have been linked to spinocerebellar ataxia type 27 (SCA27), a multisystem disorder associated with progressive deficits in motor coordination and cognitive function. Mice ( Fgf14 -/- ) lacking iFGF14 display similar phenotypes, and we have previously shown that the deficits in motor coordination reflect reduced excitability of cerebellar Purkinje neurons, owing to the loss of iFGF14-mediated regulation of the voltage-dependence of inactivation of the fast transient component of the voltage-gated Na + (Nav) current, I NaT . Here, we present the results of experiments designed to test the hypothesis that loss of iFGF14 also attenuates the intrinsic excitability of mature hippocampal and cortical pyramidal neurons. Current-clamp recordings from adult mouse hippocampal CA1 pyramidal neurons in acute in vitro slices, however, revealed that repetitive firing rates were higher in Fgf14 -/- , than in wild type (WT), cells. In addition, the waveforms of individual action potentials were altered in Fgf14 -/- hippocampal CA1 pyramidal neurons, and the loss of iFGF14 reduced the time delay between the initiation of axonal and somal action potentials. Voltage-clamp recordings revealed that the loss of iFGF14 altered the voltage-dependence of activation, but not inactivation, of I NaT in CA1 pyramidal neurons. Similar effects of the loss of iFGF14 on firing properties were evident in current-clamp recordings from layer 5 visual cortical pyramidal neurons. Additional experiments demonstrated that the loss of iFGF14 does not alter the distribution of anti-Nav1.6 or anti-ankyrin G immunofluorescence labeling intensity along the axon initial segments (AIS) of mature hippocampal CA1 or layer 5 visual cortical pyramidal neurons in situ . Taken together, the results demonstrate that, in contrast with results reported for neonatal (rat) hippocampal pyramidal neurons in dissociated cell culture, the loss of iFGF14 does not disrupt AIS architecture or Nav1.6 localization/distribution along the AIS of mature hippocampal (or cortical) pyramidal neurons in situ .

False positive urine amphetamine immunoassay due to solriamfetol

Solriamfetol is a schedule IV-controlled substance used to treat excessive daytime sleepiness resulting from narcolepsy or obstructive sleep apnea. We present a patient prescribed solriamfetol who tested positive for amphetamines on a routine urinary toxicology screen despite patient denial of illicit drug use, raising the possibility of a false positive amphetamine screen. Spiking studies were performed on negative urine, and different concentrations of solriamfetol drug on 2 different amphetamine assays: the commonly used Beckman Emit® II Plus Amphetamines Assay, and the Citrine™ Triple Quad™ MS/MS Systems. The Beckman yielded positive results for amphetamines at solriamfetol concentrations of 200 μg/mL and 2000 μg/mL and negative results at 0.2 μg/mL and 2 μg/mL. However, the Citrine™ Triple Quad™ MS/MS Systems was negative at all concentrations. The Beckman Emit® II Plus Amphetamine Assay gave false positive results for amphetamines due to solriamfetol drug usage, a finding of relevance to prescribers of solriamfetol.

Primary somatosensory cortex sensitivity may increase upon completion of a motor task

OBJECTIVES

The electroencephalogram and magnetic field primary somatosensory cortex (S1)-derived components are attenuated before and during motor tasks compared to the resting state, a phenomenon called gating; however, the S1 response after a motor task has not been well studied. We aimed to investigate sensory information processing immediately after motor tasks using magnetoencephalography.

MATERIALS AND METHODS

We investigated sensory information processing immediately after finger movement using magnetoencephalography in 14 healthy adults. Volunteers performed a simple reaction task where they were required to press a button when they received a cue. In parallel, electrical stimulation to the right index finger was applied at regular intervals to detect the magnetic brain field changes. The end of the motor task timing was defined using the event-related synchronization (ERS) appearance latency in the brain magnetic field's beta band around the primary motor cortex. The ERS appearance latency and the sensory stimuli timing applied every 500 ms were synchronized over the experimental system timeline. We examined whether there was a difference in the S1 somatosensory evoked field responses between the ERS emergence and ERS disappearance phase, focusing on the N20m-P35m peak-to-peak amplitude (N20m-P35m amplitude) value. A control experiment was also conducted in which only sensory stimulation was applied with no motor task.

RESULTS

The N20m-P35m mean amplitude value was significantly higher in the ERS emergence phase (15.81 nAm; standard deviation [SD], 6.54 nAm) than in the ERS disappearance phase (13.54 nAm; SD, 5.12 nAm) (p < 0.05) and the control (12.08 nAm, SD 5.61 nAm) (p = 0.013). No statistically significant differences were identified between the ERS disappearance phase and the control (p = 0.281).

CONCLUSIONS

The S1 sensitivity may increase rapidly after exiting from the gating influence in S1 (after completing a motor task).

Neuropeptides and small-molecule amine transmitters: cooperative signaling in the nervous system

Neuropeptides are expressed in cell-specific patterns throughout mammalian brain. Neuropeptide gene expression has been useful for clustering neurons by phenotype, based on single-cell transcriptomics, and for defining specific functional circuits throughout the brain. How neuropeptides function as first messengers in inter-neuronal communication, in cooperation with classical small-molecule amine transmitters (SMATs) is a current topic of systems neurobiology. Questions include how neuropeptides and SMATs cooperate in neurotransmission at the molecular, cellular and circuit levels; whether neuropeptides and SMATs always co-exist in neurons; where neuropeptides and SMATs are stored in the neuron, released from the neuron and acting, and at which receptors, after release; and how neuropeptides affect 'classical' transmitter function, both directly upon co-release, and indirectly, via long-term regulation of gene transcription and neuronal plasticity. Here, we review an extensive body of data about the distribution of neuropeptides and their receptors, their actions after neuronal release, and their function based on pharmacological and genetic loss- and gain-of-function experiments, that addresses these questions, fundamental to understanding brain function, and development of neuropeptide-based, and potentially combinatorial peptide/SMAT-based, neurotherapeutics.

Lost in Translation: Traversing the Complex Path from Genomics to Therapeutics in Autism Spectrum Disorder

Recent progress in the genomics of non-syndromic autism spectrum disorder (nsASD) highlights rare, large-effect, germline, heterozygous de novo coding mutations. This distinguishes nsASD from later-onset psychiatric disorders where gene discovery efforts have predominantly yielded common alleles of small effect. These differences point to distinctive opportunities for clarifying the neurobiology of nsASD and developing novel treatments. We argue that the path ahead also presents key challenges, including distinguishing human pathophysiology from the potentially pleiotropic neurobiology mediated by established risk genes. We present our view of some of the conceptual limitations of traditional studies of model organisms, suggest a strategy focused on investigating the convergence of multiple nsASD genes, and propose that the detailed characterization of the molecular and cellular landscapes of developing human brain is essential to illuminate disease mechanisms. Finally, we address how recent advances are leading to novel strategies for therapeutics that target various points along the path from genes to behavior.

Shared and derived features of cellular diversity in the human cerebral cortex

The cerebral cortex is the hallmark of the mammalian nervous system, and its large size and cellular diversity in humans support our most sophisticated cognitive abilities. Although the basic cellular organization of the cortex is conserved across mammals, cells have diversified during evolution. An increasingly integrated taxonomy of cell types, especially with the advent of single-cell transcriptomic data, has revealed an unprecedented variety of human cortical cell subtypes. Here, we broadly review the cellular composition and diversity of the mammalian brain, and how progenitor pools generate cell subtypes during development. We then discuss human cortical cells that are distinct from rodent cells, as well as the challenges and advantages of using model systems to study human cell types in health and disease.

Counter effects of Asiaticosids-D through putative neurotransmission on rotenone induced cerebral ganglionic injury in Lumbricus terrestris

Asiaticoside-D (AD) was shown to efficacy of ganglionic degenerated Lumbricus terrestris as a pioneering observation in our earlier research. Though, extract molecular mechanisms of AD for degenerative diseases (DDs) remains largely unknown. We investigated the neuroprotective effects of AD against ROT in cerebral ganglions (CGs) of degenerative L. terrestris. Worms were exposed to 0.4 ppm ROT for 7 days were subjected to co- treatment with 15 ppm of AD. After, CGs was removed. The levels oxidant, non-antioxidant, antioxidant status, ganglioside, ceramide and ceramide glycanase (CGase) were estimated. The m-RNA levels of dopamine transporter (DAT), octopamine transporter (OAT), innexins-9 (inx-9), ionotropic glutamate receptor 3 (iGlu3), heat shock proteins (hsp70), XPRLamide neuropeptide precursor, tyramine beta-hydroxylase (tbh-1) and β- adrenergic receptor kinase-2 (β-ARK2-3) by semi-qRT- PCR. The expression pattern of tyramine beta hydroxylase (TBH), glutamate receptor (iGluR), serotonin transporter (SERT), dopamine transporters (DAT), nerve growth factors (NGF), cytochrome C oxidase (COC), NADH dehydogenase subunit-1 (ND-1), neurotrophin receptor p75 (p75NTR), neuronal nitric oxiside synthase (nNOs) interleukin 1- beta (IL1-β) and tumor necrosis factor alpha (TNF-α) by western blotting. Glutaminergic, serotogenic and dopaminergic toxicity variations were also performed. The levels of oxidant, non-antioxidant, antioxidant status, lipids, proteins and m-RNAs were significantly altered (p < 0.001) on ROT-induced (group II) and their levels were significantly changes (p < 0.05) by ROT+AD in CGs. The sensitive study plan concluded the neuroprotective effects of AD against ROT induced degeneration in worms and suggest that the AD deserves future studies for its use as an effective alternative medicine that could minimize the morbidity of ganglionic degenerative diseases patients.

Transcriptional and Post-Transcriptional Mechanisms of the Development of Neocortical Lamination

The neocortex is a laminated brain structure that is the seat of higher cognitive capacity and responses, long-term memory, sensory and emotional functions, and voluntary motor behavior. Proper lamination requires that progenitor cells give rise to a neuron, that the immature neuron can migrate away from its mother cell and past other cells, and finally that the immature neuron can take its place and adopt a mature identity characterized by connectivity and gene expression; thus lamination proceeds through three steps: genesis, migration, and maturation. Each neocortical layer contains pyramidal neurons that share specific morphological and molecular characteristics that stem from their prenatal birth date. Transcription factors are dynamic proteins because of the cohort of downstream factors that they regulate. RNA-binding proteins are no less dynamic, and play important roles in every step of mRNA processing. Indeed, recent screens have uncovered post-transcriptional mechanisms as being integral regulatory mechanisms to neocortical development. Here, we summarize major aspects of neocortical laminar development, emphasizing transcriptional and post-transcriptional mechanisms, with the aim of spurring increased understanding and study of its intricacies.

Alterations in the neuropeptide galanin system in major depressive disorder involve levels of transcripts, methylation, and peptide

Major depressive disorder (MDD) is a substantial burden to patients, families, and society, but many patients cannot be treated adequately. Rodent experiments suggest that the neuropeptide galanin (GAL) and its three G protein-coupled receptors, GAL_1-3, are involved in mood regulation. To explore the translational potential of these results, we assessed the transcript levels (by quantitative PCR), DNA methylation status (by bisulfite pyrosequencing), and GAL peptide by RIA of the GAL system in postmortem brains from depressed persons who had committed suicide and controls. Transcripts for all four members were detected and showed marked regional variations, GAL and galanin receptor 1 (GALR1) being most abundant. Striking increases in GAL and GALR3 mRNA levels, especially in the noradrenergic locus coeruleus and the dorsal raphe nucleus, in parallel with decreased DNA methylation, were found in both male and female suicide subjects as compared with controls. In contrast, GAL and GALR3 transcript levels were decreased, GALR1 was increased, and DNA methylation was increased in the dorsolateral prefrontal cortex of male suicide subjects, however, there were no changes in the anterior cingulate cortex. Thus, GAL and its receptor GALR3 are differentially methylated and expressed in brains of MDD subjects in a region- and sex-specific manner. Such an epigenetic modification in GALR3, a hyperpolarizing receptor, might contribute to the dysregulation of noradrenergic and serotonergic neurons implicated in the pathogenesis of MDD. Thus, one may speculate that a GAL₃ antagonist could have antidepressant properties by disinhibiting the firing of these neurons, resulting in increased release of noradrenaline and serotonin in forebrain areas involved in mood regulation.

Misexpression of ptf1a in cortical pyramidal cells in vivo promotes an inhibitory peptidergic identity

The intracellular transcriptional milieu wields considerable influence over the induction of neuronal identity. The transcription factor Ptf1a has been proposed to act as an identity "switch" between developmentally related precursors in the spinal cord (Glasgow et al., 2005; Huang et al., 2008), retina (Fujitani et al., 2006; Dullin et al., 2007; Nakhai et al., 2007; Lelièvre et al., 2011), and cerebellum (Hoshino et al., 2005; Pascual et al., 2007; Yamada et al., 2014), where it promotes an inhibitory over an excitatory neuronal identity. In this study, we investigate the potency of Ptf1a to cell autonomously confer a specific neuronal identity outside of its endogenous environment, using mouse in utero electroporation and a conditional genetic strategy to misexpress Ptf1a exclusively in developing cortical pyramidal cells. Transcriptome profiling of Ptf1a-misexpressing cells using RNA-seq reveals that Ptf1a significantly alters pyramidal cell gene expression, upregulating numerous Ptf1a-dependent inhibitory interneuron markers and ultimately generating a gene expression profile that resembles the transcriptomes of both Ptf1a-expressing spinal interneurons and endogenous cortical interneurons. Using RNA-seq and in situ hybridization analyses, we also show that Ptf1a induces expression of the peptidergic neurotransmitter nociceptin, while minimally affecting the expression of genes linked to other neurotransmitter systems. Moreover, Ptf1a alters neuronal morphology, inducing the radial redistribution and branching of neurites in cortical pyramidal cells. Thus Ptf1a is sufficient, even in a dramatically different neuronal precursor, to cell autonomously promote characteristics of an inhibitory peptidergic identity, providing the first example of a single transcription factor that can direct an inhibitory peptidergic fate.

Superior pattern processing is the essence of the evolved human brain

Humans have long pondered the nature of their mind/brain and, particularly why its capacities for reasoning, communication and abstract thought are far superior to other species, including closely related anthropoids. This article considers superior pattern processing (SPP) as the fundamental basis of most, if not all, unique features of the human brain including intelligence, language, imagination, invention, and the belief in imaginary entities such as ghosts and gods. SPP involves the electrochemical, neuronal network-based, encoding, integration, and transfer to other individuals of perceived or mentally-fabricated patterns. During human evolution, pattern processing capabilities became increasingly sophisticated as the result of expansion of the cerebral cortex, particularly the prefrontal cortex and regions involved in processing of images. Specific patterns, real or imagined, are reinforced by emotional experiences, indoctrination and even psychedelic drugs. Impaired or dysregulated SPP is fundamental to cognitive and psychiatric disorders. A broader understanding of SPP mechanisms, and their roles in normal and abnormal function of the human brain, may enable the development of interventions that reduce irrational decisions and destructive behaviors.

Transcriptional dysregulation of neocortical circuit assembly in ASD

Autism spectrum disorders (ASDs) impair social cognition and communication, key higher-order functions centered in the human neocortex. The assembly of neocortical circuitry is a precisely regulated developmental process susceptible to genetic alterations that can ultimately affect cognitive abilities. Because ASD is an early onset neurodevelopmental disorder that disrupts functions executed by the neocortex, miswiring of neocortical circuits has been hypothesized to be an underlying mechanism of ASD. This possibility is supported by emerging genetic findings and data from imaging studies. Recent research on neocortical development has identified transcription factors as key determinants of neocortical circuit assembly, mediating diverse processes including neuronal specification, migration, and wiring. Many of these TFs (TBR1, SOX5, FEZF2, and SATB2) have been implicated in ASD. Here, I will discuss the functional roles of these transcriptional programs in neocortical circuit development and their neurobiological implications for the emerging etiology of ASD.

Transcriptional co-regulation of neuronal migration and laminar identity in the neocortex

The cerebral neocortex is segregated into six horizontal layers, each containing unique populations of molecularly and functionally distinct excitatory projection (pyramidal) neurons and inhibitory interneurons. Development of the neocortex requires the orchestrated execution of a series of crucial processes, including the migration of young neurons into appropriate positions within the nascent neocortex, and the acquisition of layer-specific neuronal identities and axonal projections. Here, we discuss emerging evidence supporting the notion that the migration and final laminar positioning of cortical neurons are also co-regulated by cell type- and layer-specific transcription factors that play concomitant roles in determining the molecular identity and axonal connectivity of these neurons. These transcriptional programs thus provide direct links between the mechanisms controlling the laminar position and identity of cortical neurons.

Opioid system and Alzheimer's disease

The opioid system may be involved in the pathogenesis of AD, including cognitive impairment, hyperphosphorylated tau, Aβ production, and neuroinflammation. Opioid receptors influence the regulation of neurotransmitters such as acetylcholine, norepinephrine, GABA, glutamate, and serotonin which have been implicated in the pathogenesis of AD. Opioid system has a close relation with Aβ generation since dysfunction of opioid receptors retards the endocytosis and degradation of BACE1 and γ-secretase and upregulates BACE1 and γ-secretase, and subsequently, the production of Aβ. Conversely, activation of opioid receptors increases the endocytosis of BACE1 and γ-secretase and downregulates BACE1 and γ-secretase, limiting the production of Aβ. The dysfunction of opioid system (opioid receptors and opioid peptides) may contribute to hyperphosphorylation of tau and neuroinflammation, and accounts for the degeneration of cholinergic neurons and cognitive impairment. Thus, the opioid system is potentially related to AD pathology and may be a very attractive drug target for novel pharmacotherapies of AD.

Pharmaceutical countermeasures have opposite effects on the utricles and semicircular canals in man

INTRODUCTION

Sensory conflicts in the vestibular system lead to motion sickness of which space motion sickness (SMS) is a special case. SMS affects up to 70% of the astronauts during the first 3 days in space. The search for effective countermeasures has led to several nonpharmacological and pharmacological approaches. The current study focuses on the effects of lorazepam (1 mg), meclizine (25 mg), promethazine (25 mg), and scopolamine (0.4 mg) on the vestibular system, with special focus on the canal and otolith functions separately.

METHODS

The study had a placebo-controlled, single blind, repeated measures design. Sixteen healthy volunteers were subjected to a total of 7 test sessions, the first and last being without intake of medication. Semicircular canal function was evaluated by means of electronystagmography and otolith function with unilateral centrifugation. The horizontal semicircular canal function was characterized by the vestibulo-ocular reflex (VOR) gain measured during earth vertical axis rotation as well as the total caloric response. The function of the utricles was represented by the utricular sensitivity, reflecting the ocular counter roll relative to the virtual induced head tilt.

RESULTS

Promethazine significantly decreased the semicircular canal and utricular parameters. Both scopolamine and lorazepam caused only a decrease in the utricular sensitivity, whereas meclizine only decreased the semicircular canal-induced VOR gain.

DISCUSSION

The results show that the drugs affected different areas of the vestibular system and that the effects can thus be attributed to the specific pharmacological properties of each drug. Meclizine, as an antihistaminergic and weak anticholinergic drug, only affected the VOR gain, suggesting a central action on the medial vestibular nucleus. The same site of action is suggested for the anticholinergic scopolamine since acetylcholine receptors are present and utricular fibers terminate here. The global vestibular suppression caused by promethazine is probably a consequence of its anticholinergic, antihistaminergic, and antidopaminergic properties. Based on the fact that lorazepam increased the affinity of gamma-aminobutyric acid (GABA) for the GABA(A)-receptor and its effects on the utriculi, the site of action seems to be the lateral vestibular nucleus.

CONCLUSION

Meclizine, scopolamine, and lorazepam selectively suppress specific parts of the vestibular system. Selective suppression of different parts of the vestibular system may be more beneficial for alleviating (space) motion sickness than general suppressive agents. Additionally, this knowledge may help the clinician in his therapeutic management of patients with either semicircular canal or otolith dysfunction.

Mechanisms of inhibition within the telencephalon: "where the wild things are"

In this review, we first provide a historical perspective of inhibitory signaling from the discovery of inhibition through to our present understanding of the diversity and mechanisms by which GABAergic interneuron populations function in different parts of the telencephalon. This is followed by a summary of the mechanisms of inhibition in the CNS. With this as a starting point, we provide an overview describing the variations in the subtypes and origins of inhibitory interneurons within the pallial and subpallial divisions of the telencephalon, with a focus on the hippocampus, somatosensory, paleo/piriform cortex, striatum, and various amygdala nuclei. Strikingly, we observe that marked variations exist in the origin and numerical balance between GABAergic interneurons and the principal cell populations in distinct regions of the telencephalon. Finally we speculate regarding the attractiveness and challenges of establishing a unifying nomenclature to describe inhibitory neuron diversity throughout the telencephalon.

Timing of cortical interneuron migration is influenced by the cortical hem

Cerebral cortical γ-aminobutyric acid (GABA)ergic interneurons originate from the basal forebrain and migrate into the cortex in 2 phases. First, interneurons cross the boundary between the developing striatum and the cortex to migrate tangentially through the cortical primordium. Second, interneurons migrate radially to their correct neocortical layer position. A previous study demonstrated that mice in which the cortical hem was genetically ablated displayed a massive reduction of Cajal-Retzius (C-R) cells in the neocortical marginal zone (MZ), thereby losing C-R cell-generated reelin in the MZ. Surprisingly, pyramidal cell migration and subsequent layering were almost normal. In contrast, we find that the timing of migration of cortical GABAergic interneurons is abnormal in hem-ablated mice. Migrating interneurons both advance precociously along their tangential path and switch prematurely from tangential to radial migration to invade the cortical plate (CP). We propose that the cortical hem is responsible for establishing cues that control the timing of interneuron migration. In particular, we suggest that loss of a repellant signal from the medial neocortex, which is greatly decreased in size in hem-ablated mice, allows the early advance of interneurons and that reduction of another secreted molecule from C-R cells, the chemokine SDF-1/CXCL12, permits early radial migration into the CP.

Visual evoked potentials in succinate semialdehyde dehydrogenase (SSADH) deficiency

In mammals, increased GABA in the central nervous system has been associated with abnormalities of visual evoked potentials (VEPs), predominantly manifested as increased latency of the major positive component P100. Accordingly, we hypothesized that patients with a defect in GABA metabolism, succinate semialdehyde dehydrogenase (SSADH) deficiency (in whom supraphysiological levels of GABA accumulate), would manifest VEP anomalies. We evaluated VEPs on two patients with confirmed SSADH deficiency. Whereas the P100 latencies and amplitudes for binocular VEP analyses were within normal ranges for both patients, the P100 latencies were markedly delayed for left eye (OS) (and right eye (OD), patient 1) and monocular OS (patient 2): 134-147 ms; normal <118 ms. We hypothesize that elevated GABA in ocular tissue of SSADH patients leads to a use-dependent downregulation of the major GABAergic receptor in eye, GABA(C), and that the VEP recordings' abnormalities, as evidenced by P100 latency and/or amplitude measurements, may be reflective of abnormalities within visual systems. This is a preliminary finding that may suggest the utility of performing VEP analysis in a larger sample of SSADH-deficient patients, and encourage a neurophysiological assessment of GABA(C) receptor function in Aldh5a1(-/-) mice to reveal new pathophysiological mechanisms of this rare disorder of GABA degradation.

Non-sensory cortical and subcortical connections of the primary auditory cortex in Mongolian gerbils: bottom-up and top-down processing of neuronal information via field AI

In the present study, we will provide further anatomical evidence that the primary auditory cortex (field AI) is not only involved in sensory processing of its own modality, but also in complex bottom-up and top-down processing of multimodal information. We have recently shown that AI in the Mongolian gerbil (Meriones unguiculatus) has substantial connections with non-auditory sensory and multisensory brain structures [Budinger, E., Heil, P., Hess, A., Scheich, H., 2006. Multisensory processing via early cortical stages: Connections of the primary auditory cortical field with other sensory systems. Neuroscience 143, 1065-1083]. Here we will report about the direct connections of AI with non-sensory cortical areas and subcortical structures. We approached this issue by means of the axonal transport of the sensitive bidirectional neuronal tracers fluorescein-labelled (FD) and tetramethylrhodamine-labelled dextran (TMRD), which were simultaneously injected into different frequency regions of the gerbil's AI. Of the total number of retrogradely labelled cell bodies found in non-sensory brain areas, which identify cells of origin of direct projections to AI, approximately 24% were in cortical areas and 76% in subcortical structures. Of the cell bodies in the cortical areas, about 4.4% were located in the orbital, 11.1% in the infralimbic medial prefrontal (areas DPC, IL), 18.2% in the cingulate (3.2% in CG1, 2.9% in CG2, 12.1% in CG3), 9.5% in the frontal association (area Fr2), 12.0% in the insular (areas AI, DI), 10.8% in the retrosplenial, and 34.0% in the perirhinal cortex. The cortical regions with retrogradely labelled cells, as well as the entorhinal cortex, also contained anterogradely labelled axons and their terminations, which means that they are also target areas of direct projections from AI. The laminar pattern of corticocortical connections indicates that AI receives primarily cortical feedback-type inputs and projects in a feedforward manner to its target areas. The high number of double-labelled somata, the non-topographic distribution of single FD- and TMRD-labelled somata, and the overlapping spatial distribution of FD- and TMRD-labelled axonal elements suggest rather non-tonotopic connections between AI and the multimodal cortices. Of the labelled cell bodies in the subcortical structures, about 38.8% were located in the ipsilateral basal forebrain (10.6% in the lateral amygdala LA, 11.5% in the globus pallidus GP, 3.7% in the ventral pallidum VPa, 13.0% in the nucleus basalis NB), 13.1% in the ipsi- and contralateral diencephalon (6.4% in the posterior paraventricular thalamic nuclei, 6.7% in the hypothalamic area), and 48.1% in the midbrain (20.0% in the ipsilateral substantia nigra, 9.8% in the ipsi- and contralateral ventral tegmental area, 5.0% in the ipsi- and contralateral locus coeruleus, 13.3% the ipsi- and contralateral dorsal raphe nuclei). Thus, the majority of subcortical inputs to AI was related to different neurotransmitter systems. Anterograde labelling was only found in some ipsilateral basal forebrain structures, namely, the LA, basolateral amygdala, GP, VPa, and NB. As for the cortex, the proportion and spatial distribution of single FD-, TMRD-, and double-labelled neuronal elements suggests rather non-tonotopic connections between AI and the neuromodulatory subcortical structures.

Changes in dopamine D2 receptors and 6-[18F]fluoro-L-3,4-dihydroxyphenylalanine uptake in the brain of 6-hydroxydopamine-lesioned rats

We studied tracer distributions in positron emission tomography of ligands for dopamine D1 receptors ([11C]SCH23390) and D2 receptors ([11C]raclopride) and the dopamine precursor analog 6-[18F]fluoro-L-3,4-dihydroxyphenylalanine ([18F]FDOPA), as a measurement of presynaptic dopaminergic function, in the brain after 6-hydroxydopamine lesioning of the medial forebrain bundle in rats. The unilateral lesions were confirmed behaviorally by methamphetamine-induced rotation 2 weeks after lesioning, and the brains were analyzed by tissue dissection following an intravenous bolus of each tracer 3 weeks after lesioning. [11C]Raclopride, but not [11C]SCH23390, showed a higher accumulation in the striatum on the lesion side compared with that on the non-lesioned (intact) side. On the other hand, a lower accumulation of [18F]FDOPA was found in the striatum and cerebral cortex on the lesion side. Our studies demonstrate upregulation of dopamine D2 receptors in the striatum and a decrease in FDOPA uptake in both the striatum and cerebral cortex ipsilateral to the 6-hydroxydopamine lesions. Therefore, the combination of a D2 antagonist and FDOPA may provide a potentially useful method for assessing the effects of dopamine depletion in Parkinson's disease.

Upregulation of astrocytic basic fibroblast growth factor in the cingulate cortex of lactating rats: time course and role of suckling stimulation

Previous work from our laboratory has shown that there is a much higher level of bFGF and GFAP immunoreactivity in area 2 of the cingulate cortex (Cg2) of rats on day 16 of lactation than in cycling or late pregnant females. To examine the time course of this change, in the first of the current studies, we compared bFGF and GFAP immunoreactivity in the brains of lactating females on postpartum day 4 (PP4), day 10 (PP10), day 16 (PP16), and day 24 (PP24) with that of cycling and ovariectomized (OVX) females. In the second study, we investigated whether the maintenance of these changes in bFGF and GFAP depended on suckling stimulation by removing litters on day 1 or day 16 postpartum and examining the brains of the dams on day 4 (Pr4) or day 24 (Pr24) postpartum, respectively. bFGF and GFAP immunoreactivity within Cg2 and the medial preoptic area (MPOA) were measured. In both experiments astrocytic bFGF and GFAP surface density in the Cg2 varied significantly across groups. All postpartum rats, regardless of stage of lactation or presence of the litter, had significantly higher levels of bFGF and GFAP immunoreactivity than cycling animals. Thus, the maintenance of this upregulation in bFGF and GFAP immunoreactivity does not depend on suckling stimulation. Consistent with our previous report, astrocytic bFGF was also elevated in the MPOA of PP16 animals. These data suggest a robust, long-lasting, postpartum change in bFGF and GFAP immunoreactivity in Cg2 and a role for this area of the cortex in the physiological and behavioral adaptations that accompany reproductive experience.

Serotoninergic activation of the basolateral amygdala and modulation of tonic immobility in guinea pig

Tonic immobility (TI), also known as death feigning or animal hypnosis, is a reversible state of motor inhibition that is not only triggered by postural inversion and/or movement restraining maneuvers but also by repetitive stimulation and pressure on body parts. Evidence has demonstrated that the basolateral nucleus of the amygdala (BLA) is particularly associated with defensive behavior that involves the emotional states of fear and anxiety. In addition, some reports have demonstrated that serotonin (5-HT) released in the amygdala is increased during states of stress and anxiety, principally in the BLA. In the present study, we investigated the effects of serotonergic activation of the BLA on the duration of TI. The results showed that the microinjection of 5-HT (3.0 microg) into the BLA decreased the duration of TI. Similarly, the administration of a 5-HT1A agonist (0.1 microg of 8-hydroxy-dipropylaminotretalin) or 5-HT2 agonist (0.1 microg of alpha-methyl-5-HT) into the BLA reduced the TI duration. The effect of 5-HT2 agonist was reversed by pretreatment with a dose that had no effect per se (0.01 microg) of ketanserin (5-HT2 receptor antagonists) into the BLA. Moreover, the activation of 5-HT1A and 5-HT2 receptors in the BLA did not alter the spontaneous motor activity in the open field test. The results of the present study indicate that the serotonergic system of the BLA possibly produces a reduction in fear and/or anxiety that reduces the TI duration in guinea pigs, but this is not due to increased spontaneous motor activity induced by serotonergic activation, which might affect TI duration non-specifically.

Effect of prenatal exposure to ethanol on glutamate and GABA immunoreactivity in macaque somatosensory and motor cortices: Critical timing of exposure

The present study explored the effects of gestational ethanol exposure on enduring changes in the distribution of projection neurons and local circuit neurons in somatosensory/motor cortex. Critical events in corticogenesis occur during macaque gestation: the first six weeks of gestation include the period of primary stem cell production and the next 18 weeks are marked by the birth, migration, early differentiation, and death of cortical neurons. Monkeys were exposed to ethanol (or saline) one day per week during the first six or during the entire 24 weeks of gestation. Offspring were killed as adolescents. Projection neurons and local circuit neurons were identified immunohistochemically with antibodies directed against glutamate and anti-GABA, respectively. In all animals, both projection neurons and local circuit neurons were distributed in all laminae of both somatosensory and motor cortices. Ethanol did not affect the size of Cresyl Violet-stained, glutamate-positive, or GABA-immunolabeled somata, however, it did decrease neuronal density. The total density of Cresyl Violet-stained neurons was reduced in monkeys treated with ethanol (or saline) one day per week during the first six weeks of gestation and during the entire 24 weeks of gestation. Similar reductions were detected for glutamate- and GABA-positive neurons. The densities of Cresyl Violet-stained and of glutamate- and GABA-expressing neurons were reduced in all cortical layers. The only exception was layer V which was unaffected in monkeys treated with ethanol (or saline) one day per week during the first six weeks of gestation and during the entire 24 weeks of gestation. Thus, the parallel effects on both neuronal subpopulations suggest that ethanol targets a population of undetermined neuronal precursors.

Short-term visual deprivation alters neural processing of tactile form

Blindness is known to alter the responsiveness of visual cortex. Recently, reversible visual deprivation by blindfolding has been shown to affect non-visual abilities as well as visual cortical function. Here we investigated the effect of 2 h of blindfolding on cerebral cortical activation patterns during tactile form perception, using functional magnetic resonance imaging. Two form tasks were used, one requiring discrimination of global stimulus form and the other, detection of a gap in a bar. Blindfolded subjects showed significant deactivation during these tasks in regions that are intermediate in the hierarchy of visual shape processing: probable V3A and ventral intraparietal sulcus (vIPS). These regions lacked signal changes in controls. There were also task-specific increases in activation in blindfolded relative to control subjects, favoring the form over the gap task, along the IPS and in regions of frontal and temporal cortex. We also found alterations of functional connectivity that corresponded to the activity differences, with the emergence of correlated activity between the vIPS and V3A in blindfolded subjects. We conclude that blindfolding sighted individuals for a 2-h period induces significant changes in the neural processing of tactile form, probably reflecting short-term neural plasticity.

Epilepsy and Medication Effects on the Pattern Visual Evoked Potential*

Visual disruption in patients diagnosed with epilepsy may be attributable to either the disease itself or to the anti-epileptic drugs prescribed to control the seizures. Effects on visual function may be due to perturbations of the GABAergic neurotransmitter system, since deficits in GABAergic cortical interneurons have been hypothesized to underlie some forms of epilepsy, some anti-epileptic medications increase cortical GABA levels, and GABAergic neural circuitry plays an important role in mediating the responses of cells in the visual cortex and retina. This paper characterizes the effects of epilepsy and epilepsy medications on the visual evoked response to patterned stimuli. Steady-state visual evoked potentials (VEP) evoked by onset-offset modulation of high-contrast sine-wave stimuli were measured in 24 control and 54 epileptic patients. Comparisons of VEP spectral amplitude as a function of spatial frequency were made between controls, complex partial, and generalized epilepsy groups. The effects of the GABA-active medication valproate were compared to those of carbamezepine. The amplitude of the fundamental (F1) component of the VEP was found to be sensitive to epilepsy type. Test subjects with generalized epilepsy had F1 spatial frequency-amplitude functions with peaks shifted to lower spatial frequencies relative to controls and test subjects with complex partial epilepsy. This shift may be due to reduced intracortical inhibition in the subjects with generalized epilepsy. The second harmonic component (F2) response was sensitive to medication effects. Complex partial epilepsy patients on VPA therapies showed reduced F2 response amplitude across spatial frequencies, consistent with previous findings that showed the F2 response is sensitive to GABA-ergic effects on transient components of the VEP.

A comparative analysis of transcribed genes in the mouse hypothalamus and neocortex reveals chromosomal clustering

The hypothalamus and neocortex are subdivisions of the mammalian forebrain, and yet, they have vastly different evolutionary histories, cytoarchitecture, and biological functions. In an attempt to define these attributes in terms of their genetic activity, we have compared their genetic repertoires by using the Serial Analysis of Gene Expression database. From a comparison of 78,784 hypothalamus tags with 125,296 neocortical tags, we demonstrate that each structure possesses a different transcriptional profile in terms of gene ontological characteristics and expression levels. Despite its more recent evolutionary history, the neocortex has a more complex pattern of gene activity. Gene identities and levels of gene expression were mapped to their chromosomal positions by using in silico definition of GC-rich and GC-poor genome bands. This analysis shows contrasting views of gene activity on a genome scale that is unique to each brain substructure. We show that genes that are more highly expressed in one tissue tend to be clustered together on a chromosomal scale, further defining the genetic identity of either the hypothalamus or neocortex. We propose that physical proximity of coregulated genes may facilitate transcriptional access to the genetic substrates of evolutionary selection that ultimately shape the functional subdivisions of the mammalian brain.

Substance P and nitric oxide signaling in cerebral cortex: anatomical evidence for reciprocal signaling between two classes of interneurons

Parvalbumin-containing fast-spiking interneurons in the cerebral cortex exhibit widespread electrical coupling, as do somatostatin-containing low-threshold spiking interneurons. Besides the classical neurotransmitter gamma-aminobutyric acid, these cortical interneurons may also release various neuropeptides including substance P (SP), as well as the freely diffusible messenger nitric oxide (NO). To investigate whether these two networks of interneurons might interact via these nonclassical messengers, we performed immunocytochemistry for SP and NO signaling pathways in rat somatic sensory cortex. SP was found in a subset of parvalbumin-positive cells concentrated in layers IV and V, whereas its receptor, NK1, was found in a subset of somatostatin-containing neurons (and also, at much lower levels, in a disjoint subset of parvalbumin-containing neurons). Only 4% of SP-containing axon terminals were apposed to NK1-positive dendrites, suggesting that in the cerebral cortex, SP may act predominantly as a paracrine neuromediator. Nitric oxide synthase-I (NOS-I), the synthetic enzyme for NO, was found almost exclusively in NK1-positive neurons; 95% of intensely somatostatin/NK1-positive neurons were also positive for NOS-I, and 94% of NOS-positive neurons were also positive for NK1. Immunoreactivity for soluble guanylyl cyclase (the NO receptor) was at high levels in the apical dendrites of layer V pyramidal neurons and in parvalbumin/SP-positive neurons. These data point to a novel reciprocal chemical interaction between two inhibitory networks in the rat neocortex.

The acetylcholine release enhancer linopirdine induces Fos in neocortex of aged rats

Centrally acting cholinergic agents induce the immediate early gene c-fos in the rat brain resulting in transient increases of Fos protein, most notably in the cerebral cortex. In this study we have monitored by Fos immunohistochemistry the effect of the acetylcholine release enhancer linopirdine (DUP996) on the immediate early gene c-fos in brains of 3 months and 30 months old rats. In young rats linopirdine had only a marginal effect on Fos expression. In contrast, in aged rats linopirdine caused widespread expression of Fos throughout neocortex. In somatosensory cortex, the induction of the c-fos gene by linopirdine was nearly completely blocked by atropine and scopolamine and strongly attenuated by the NMDA receptor blockers CPP and MK-801. The results suggest that the age-related decline in acetylcholine release in rodents can be partially compensated for by administration of linopirdine.

Transplanted neuroblasts differentiate appropriately into projection neurons with correct neurotransmitter and receptor phenotype in neocortex undergoing targeted projection neuron degeneration

Reconstruction of complex neocortical and other CNS circuitry may be possible via transplantation of appropriate neural precursors, guided by cellular and molecular controls. Although cellular repopulation and complex circuitry repair may make possible new avenues of treatment for degenerative, developmental, or acquired CNS diseases, functional integration may depend critically on specificity of neuronal synaptic integration and appropriate neurotransmitter/receptor phenotype. The current study investigated neurotransmitter and receptor phenotypes of newly incorporated neurons after transplantation in regions of targeted neuronal degeneration of cortical callosal projection neurons (CPNs). Donor neuroblasts were compared to the population of normal endogenous CPNs in their expression of appropriate neurotransmitters (glutamate, aspartate, and GABA) and receptors (kainate-R, AMPA-R, NMDA-R. and GABA-R), and the time course over which this phenotype developed after transplantation. Transplanted immature neuroblasts from embryonic day 17 (E17) primary somatosensory (S1) cortex migrated to cortical layers undergoing degeneration, differentiated to a mature CPN phenotype, and received synaptic input from other neurons. In addition, 23.1 +/- 13.6% of the donor-derived neurons extended appropriate long-distance callosal projections to the contralateral S1 cortex. The percentage of donor-derived neurons expressing appropriate neurotransmitters and receptors showed a steady increase with time, reaching numbers equivalent to adult endogenous CPNs by 4-16 weeks after transplantation. These results suggest that previously demonstrated changes in gene expression induced by synchronous apoptotic degeneration of adult CPNs create a cellular and molecular environment that is both permissive and instructive for the specific and appropriate maturation of transplanted neuroblasts. These experiments demonstrate, for the first time, that newly repopulating neurons can undergo directed differentiation with high fidelity of their neurotransmitter and receptor phenotype, toward reconstruction of complex CNS circuitry.

Cell proliferation and death: morphological evidence during corticogenesis in the developing human brain

Cell proliferation and death account for the refinement of the cell number during corticogenesis. These processes have been investigated in the human developing telencephalon (12th-24th week of gestation) and cerebellum (16th-24th week). Only foetal brains, which had normal neuropathological examination, were utilised. Cell proliferation was analysed by classical histology and PCNA immunohistochemistry; cell death was investigated by the TUNEL method, which makes evident the different stages of apoptosis. High figures of mitotic nuclei were seen in the ventricular zone at the 12th-15th week of gestation, before sharply declining. The decrease of the proliferating cells occurs synchronously in both frontal and occipital germinal zones. Conversely, a slow increase of the number of the mitotic cells was observed in the more dorsal regions, probably due to the presence of proliferating glial elements. The amount of apoptotic nuclei was always remarkably low in the transient compartments of the wall of the telencephalon. The moderate number of apoptotic cells suggests that cellular mechanisms other than apoptosis are involved in the dissolution of the ventricular zone. Neither proliferating nor apoptotic cells were seen in the cortical plate. The topography of cell proliferation and death in the developing cerebellum did not account for a mutual relationship between the two events. The prolonged duration of the cell-cycle in the human developing CNS may explain its increased vulnerability to various DNA-damaging conditions, which can lead to either destructive lesions or malformations.

Comparative analysis of calcium-binding protein-immunoreactive neuronal populations in the auditory and visual systems of the bottlenose dolphin (Tursiops truncatus) and the macaque monkey (Macaca fascicularis)

This study compares the distribution of three calcium-binding protein-immunoreactive (CaBP-immunoreactive) neuronal populations (calretinin-, calbindin- and parvalbumin-immunoreactive) in the visual and auditory systems in two mammalian species which are fundamentally different in their evolutionary traits and ecology, the aquatic toothed whale Tursiops truncatus (bottlenose dolphin) and the terrestrial Old World primate, Macaca fascicularis (long-tailed macaque). Immunocytochemical analyses, combined with computerized morphometry revealed that in the visual and auditory systems of the bottlenose dolphin, calretinin and calbindin are the prevalent calcium-binding proteins, whereas parvalbumin is present in very few neurons. The prevalence of calretinin and calbindin-immunoreactive neurons is especially obvious in the auditory system of this species. In both auditory and visual systems of the macaque monkey, the parvalbumin-immunoreactive neurons are present in comparable or higher densities than the calretinin and calbindin-immunoreactive neurons. In some structures of the visual and auditory systems of the macaque monkey, the calretinin- and calbindin-immunoreactive neurons are nearly absent. The prevalence of parvalbumin-immunoreactive over calretinin- and calbindin-immunoreactive neurons is particularly prominent in the visual system of primates. Thus, the dominant sensory systems in both aquatic and terrestrial mammals are enriched in specific phenotypes of calcium-binding protein-immunoreactive neurons.

Five discrete cis-active domains direct cell type-specific transcription of the vasoactive intestinal peptide (VIP) gene

Vasoactive intestinal peptide (VIP) is a neuromodulator expressed with great anatomical specificity throughout the nervous system. Cell-specific expression of the VIP gene is mediated by a tissue specifier element (TSE) located within a 2.7-kilobase (kb) region between -5.2 and -2.5 kb upstream from the transcription start site, and requires an intact promoter proximal VIP-CRE (cyclic AMP-responsive element) (Hahm, S. H., and Eiden, L. E. (1997) J. Neurochem. 67, 1872-1881). We now report that the TSE comprises a 425-base pair domain located between -4.7 and -4.2 kb containing two AT-rich octamer-like sequences. The 425-base pair TSE is sufficient to provide full cell-specific regulation of the VIP gene, when fused to the 5' proximal 1.55 kb of the VIP gene. Mutational analysis and gel shift assays of these octamer-like sequences indicate that the binding of proteins related to the ubiquitously expressed POU-homeodomain proteins Oct-1 and/or Oct-2 to these octamer-like sequences plays a central role for the function of the TSE. The TSE interacts with three additional discrete domains besides the cAMP response element, which are located within the proximal 1.55 kb of the VIP gene, to provide cell-specific expression. An upstream domain from -1.55 to -1.37 kb contains E-boxes and MEF2-like motifs, and deletion of this domain results in complete abrogation of cell-specific transcriptional activity. The region from -1.37 to -1. 28 kb contains a STAT motif, and further removal of this domain allows the upstream TSE to act as an enhancer in both SH-EP and HeLa cells. The sequence from -1.28 to -0.9 kb containing a non-canonical AP-1 binding sequence (Symes, A., Gearan, T., Eby, J., and Fink, J. S. (1997) J. Biol. Chem. 272, 9648-9654), is absolutely required for TSE-dependent cellspecific expression of the VIP gene. Thus, five discrete domains of the VIP gene provide a combination of enhancer and repressor activities, each completely contingent on VIP gene context, that together result in cell-specific transcription of the VIP gene.

Neurotransmitter and amino acid analysis and ultrastructural observations of fetal brain cortex transplantation to adult rat brain under the effect of dexamethasone

OBJECTIVE

To conduct an investigation of fetal cortical tissue graft survival using transmission electron microscopy and analyzing neurotransmitters and amino acids and their function, with special reference to the effect of dexamethasone.

METHODS

Transplantation of fetal cortical brain tissue to 100 adult Wistar albino rats weighing 170 to 220 g was performed. The rats were divided into three groups. Only transplantation of fetal cortical brain tissue was performed in the first group (n=36). In the second group (n=48), dexamethasone was administered in addition to fetal cortical tissue transplantation. The third group (n=16) was used as the surgical control group. The rats were allowed to live for 6 weeks and were then decapitated. The grafts were examined by electron microscopy. Additionally, quantitative analyses of the neurotransmitters and amino acids of the grafts were conducted using high-pressure liquid chromatography.

RESULTS

Electron microscopic observations revealed that the grafts were still surviving at the end of the 6th week in both groups. However, in the group that received dexamethasone, neurons and their organelles were better developed than in the group that did not receive dexamethasone. Concommitantly, results of quantitative analysis in the dexamethasone group revealed statistically extremely significant higher amino acid values for glutamic acid, aspartic acid, beta-alanine, and lysine and significantly higher values for gamma-aminobutyric acid, glutamine, glycine, and serine when compared to the nondexamethasone group.

CONCLUSION

Dexamethasone is effective in increasing the survival and in developing the ultrastructural and functional outcome of transplanted neurons in fetal grafts.

Molecular heterogeneity of Vicia villosa-recognized perineuronal nets surrounding pyramidal and nonpyramidal neurons in the guinea pig cerebral cortex

Of three monoclonal antibodies (mAbs Cat 301, 1B5 and 473) which recognize epitopes on perineuronal nets (PnNs), only mAb 473 displayed considerably varied degrees of staining intensity on Vicia villosa-labeled pyramidal (P) neurons (5%, intensely; 54%, very weakly; and 41%, unstained). These results indicate the heterogeneity on molecular structure or composition of the terminal N-acetylgalactosamine-containing PnNs within P class as well as between P and nonpyramidal classes.

Fos induction in subtypes of cerebrocortical neurons following single picrotoxin-induced seizures

In adult rats single seizures of varying behavioural severities were caused by slow, systemic infusion of picrotoxin, an antagonist of the C1- channel at the GABAA receptor. We used a double labelling immunohistochemical method to define the subclasses of neurons that contained Fos protein following seizures. In four cortical regions (piriform, entorhinal, motor and sensory) neuronal subclasses were defined with antibodies against the calcium-binding proteins D-28K, parvalbumin and calretinin (aspiny neurons), and neurofilament protein (spiny neurons). The remaining spiny neuron population was estimated by subtraction of defined subclasses from total neuronal numbers determined from Nissl stain. After seizures, most of the calbindin D-28K immunoreactive interneurons (> 80%) and many of the unlabelled spiny neurons (60-80%) were FOs positive. Co-localisation of Fos was found in about 30% of parvalbumin, calretinin and neurofilament protein immunoreactive neurons. Paradoxically, mild seizures were associated with induction of Fos in up to 80% of cortical cells and more severe seizures with 60%, the difference being due to different levels of Fos induction in spiny neurons. These results also demonstrate that seizures induce Fos predominantly in excitatory cortical neurons.

Amino acid concentrations and selected enzyme activities in rat auditory, olfactory, and visual systems

Homogenates of specific brain regions of three sensory systems (auditory, olfactory, and visual) were prepared from pigmented Long-Evans Hooded rats and assayed for amino acid concentrations and activities of glutaminase, aspartate aminotransferase (total, cytosolic, and by difference, mitochondrial), malate dehydrogenase, lactate dehydrogenase, and choline acetyltransferase. Comparing the quantitative distributions among regions revealed significant correlations between AAT and aspartate, between glutaminase and glutamate, between glutamate and glutamine, and between AAT plus glutaminase, or glutaminase alone, and the sum of aspartate, glutamate, and GABA, suggesting a metabolic pathway involving the synthesis of a glutamate pool as precursor to aspartate and GABA. Of the inhibitory transmitter amino acids, GABA concentrations routinely exceeded those of glycine, but glycine concentrations were relatively high in brainstem auditory structures.

The electrophysiological effects of multiple subpial transection (MST) in an experimental model of epilepsy induced by cortical stimulation

Multiple subpial transection (MST) is an effective surgical therapy for patients with intractable seizures whose epileptogenic lesions lie in the cortex and are unresectable. Morrell developed this procedure and reported clinical results obtained using it. However, only the disappearance of epileptiform discharges after MST in an experimental model of epilepsy has been demonstrated. The aim of this study was to establish the histological changes caused by MST and evaluate the effects of this procedure on interneuronal discharge spread in an epilepsy model, i.e. acute cortical kindling in rabbits. Histologically, vertical cracks in the transected cortex with mild gliosis and very little tissue disruption were observed. Horizontal fibers across the crack had been transected, whereas vertical fibers and neuronal cell bodies were preserved. The stimulation-induced after-discharges (ADs) were analyzed: cortical hyperactivity across the transected zone was reduced significantly earlier than that in the control group. Propagation of ADs induced by the kindling effect was also inhibited. These results suggest that MST interrupts not only neuronal synchronization, but also excitatory interneuronal conduction, in this epilepsy model.

Synaptic relationship between substance P and the substance P receptor: light and electron microscopic characterization of the mismatch between neuropeptides and their receptors

Light microscopic studies have demonstrated significant mismatches in the location of neuropeptides and their respective binding sites in the central nervous system. In the present study we used an antiserum raised against a synthetic peptide corresponding to the carboxyl-terminal tail of the substance P (SP) receptor (SPR) to further explore the relationship between a neuropeptide and its receptor. Light microscopy revealed an excellent correlation between the patterns of SPR immunoreactivity and of 125I-labeled SPR-binding sites in the central nervous system. The SPR appeared to be exclusively expressed by neurons; in fact, the SPR decorates the somatic and dendritic surface of neurons, producing Golgi-like images. Electron microscopic analysis in cortex, striatum, and spinal cord revealed that approximately 70% of the surface membrane of immunoreactive neurons is SPR laden. Simultaneous electron microscopic labeling of SP and SPR demonstrated significant mismatch at the synaptic level. Although some SP terminals contacted SPR-immunoreactive membrane, no more than 15% of the SPR-laden membrane apposed synaptic terminals. These results suggest that in contrast to more "classical" central and peripheral nervous system synapses, wherein the receptor immediately apposes the site of neurotransmitter storage and release, much of the surface of SPR-expressing neurons can be targeted by SP that diffuses a considerable distance from its site of release.

Intermediary metabolism disturbance in AD/SDAT and its relation to molecular events

1. Early-onset dementia of Alzheimer type (EODAT; AD) and late-onset dementia of Alzheimer type (LODAT; SDAT) are heterogenous in origin. 2. A common superordinate pathobiochemical principle in the etiopathogenesis of both types of dementia is neuronal energy failure with subsequent abnormalities in cellular Ca2+ homeostasis and glucose-related amino acid metabolism. 3. These metabolic abnormalities are assumed to occur first at axodendritic terminals of the acetylcholinergic-glutamatergic circuit and to cause morphological damage at synaptic sites. 4. Metabolic stress and structural damage at synaptic sites may induce enhanced formation of APP and its cleavage product amyloid. 5. Energy-metabolism related abnormalities along with functional and structural changes at synaptic sites of the acetylcholinergic-glutamatergic circuit may precede the formation of amyloid in DAT brain.

Chromogranin A, a soluble synaptic vesicle protein, is found in cortical neurons other than previously defined peptidergic neurons in the human neocortex

Neuropeptides in the cerebral cortex have previously been identified in non-pyramidal neurons only. By comparing the location of chromogranin A (CgA), a soluble protein of large dense-core synaptic vesicles, with that of SMI-32, neuropeptide Y (NPY), parvalbumin (PV) and calbindin (CaBP) using double label immunohistochemistry, we demonstrate that CgA is present in pyramidal neurons as well as in several subtypes of non-pyramidal neurons.

Immunoreactivity for GAD and three peptides in somatosensory cortex and thalamus of the raccoon

Immunocytochemical methods were used to determine the distributions of glutamic acid decarboxylase (GAD), vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK), and somatostatin (SOM) in the primary somatosensory cortex and somatosensory thalamus of adult raccoons. The cortex showed extensive immunoreactivity for GAD, revealing a large population of GABAergic neurons. GAD-labeled cells were numerous in all cortical layers, but were most concentrated in laminae II-IV. The cells were nonpyramidal and of varying morphology, typically with somata of small or medium size. GAD-immunoreactive puncta, presumably synaptic terminals, were widespread and often appeared to end on both GAD-negative and GAD-positive neurons. Immunoreactivity for the peptides was much less extensive than that for GAD, with the number of labeled neurons for VIP > CCK > SOM. Peptidergic cells were preferentially located in the upper and middle cortical layers, especially laminae II and III. The cells were nonpyramidal, often bitufted or bipolar in morphology, and small to medium in size. Their processes formed diffuse plexuses of fibers with terminal-like varicosities that occasionally surrounded nonpeptidergic neurons. The thalamus showed a clearly differentiated pattern of immunoreactivity for GAD, but little or no labeling for the three peptides. Nuclei adjoining the ventral posterior lateral (VPL)/ventral posterior medial (VPM) complex--including the reticular nucleus--contained many GAD-positive neurons and fibers. In contrast, the VPL and VPM nuclei displayed considerably less GAD immunoreactivity, somewhat surprising given the raccoon's highly developed somatosensory system. However, the ventral posterior inferior (VPI) nucleus revealed rather dense GAD labeling, perhaps related to a specialized role in sensory information processing. Thus, the primary somatosensory cortex of the raccoon showed patterns of immunoreactivity for GAD and peptides that were similar to those of other species; the somatosensory thalamus revealed a distinctive profile of GAD immunoreactivity, with labeling that was light to moderate in the VPL/VPM complex and relatively extensive in VPL.

The cortical lesion of Huntington's disease: further neurochemical characterization, and reproduction of some of the histological and neurochemical features by N-methyl-D-aspartate lesions of rat cortex

Huntington's disease is a progressive neurodegenerative disease in which the basal ganglia are preferentially affected. Recent evidence, however, suggests involvement of the cerebral cortex as well, with sparing of neurochemically defined subsets of gamma-aminobutyric acid (GABA)-ergic interneurons. In the present study, we examined changes in concentrations of the amino acid neurotransmitters GABA, glutamate, and aspartate in nine cortical regions from 23 patients with advanced Huntington's disease and 12 control brains. GABA concentrations were significantly increased in eight of the nine regions, consistent with a sparing of GABAergic local circuit neurons in the context of progressive cortical atrophy. Small but significant increases in glutamate were found in six of the nine regions, while aspartate levels were generally unaffected. Striate cortex (Brodmann's area 17) showed the most profound increases in GABA and glutamate. We also investigated the effects of powdering the excitotoxins N-methyl-D-aspartate (NMDA) or kainic acid onto the dura of rats. The resulting lesions were examined at 1 week and 6 months. The NMDA-induced lesions showed striking sparing of parvalbumin-positive neurons (a subset of GABAergic interneurons), and this sparing was reflected in neurochemical measurements of GABA; kainic acid lesions failed to display this selectivity. Somatostatin, cholecystokinin, and vasoactive intestinal polypeptide concentrations were spared by the NMDA-induced lesions, and substance P levels were significantly increased. These results provide evidence that NMDA excitotoxic lesions of cerebral cortex can produce a selective pattern of neuronal damage similar to that which occurs in Huntington's disease.

High-Resolution Light and Electron Microscopic Immunocytochemistry of Colocalized GABA and Calbindin D-28k in Somata and Double Bouquet Cell Axons of Monkey Somatosensory Cortex

A simple method for high-resolution immunocytochemical colocalization of different antigens in semithin sections 1 - 3 microm thick was used to study the colocalization of the calcium binding protein calbindin D-28k (calbindin) with gamma-aminobutyric acid (GABA) in double bouquet cells of monkey (Macaca fuscata) somatosensory cortex. Double bouquet cells were first visualized in vibratome sections by pre-embedding immunocytochemical staining for calbindin. Sections containing calbindin-immunoreactive somata and double bouquet cell axons were then osmicated, embedded in Araldite, resectioned at 1 - 3 microm and stained for GABA by postembedding immunocytochemistry after elution of the bound anti-calbindin antibodies. Other semithin sections adjacent to those eluted and still containing calbindin immunoreactive somata and processes were resectioned at 60 - 70 nm for electron microscopy and stained immunocytochemically for GABA by the postembedding immunogold procedure. Calbindin-positive cells are most numerous in layer II and upper layer III, where they outnumber those in all other layers combined. In layers II and upper III, approximately 30% of the stained cells are pyramidal and do not colocalize GABA. Only approximately two-thirds of the calbindin-stained nonpyramidal cells in these layers colocalize GABA, but among these virtually all the calbindin-positive double bouquet cells and their axons are GABA-immunoreactive. In deeper layers all calbindin-positive cells are nonpyramidal and all colocalize GABA. At the electron microscopic level, however, significant numbers of calbindin-positive axon terminals making symmetrical synapses are not GABA-immunoreactive. These results suggest the calbindin cells of monkey somatosensory cortex are a heterogeneous population that includes GABAergic and non-GABAergic cell types.

Time of origin of cortico-collicular projection neurons in the rat visual cortex

The time of origin and the radial gradient of neurogenesis of cortico-collicular neurons have been studied in the rat visual area 17. We used a combined technique for the histochemical detection of the retrogradely transported horseradish peroxidase from the superior colliculus and the autoradiographic detection of the [3H]-thymidine administered during the gestational period. The cortico-collicular neurons of visual area 17 are located in layer V and are generated on gestational day (GD) 15 (59.78%), GD 16 (36.21%), and GD 17 (4.01%). This finding reveals that, for the cortico-collicular neuronal population, the birth date is well-correlated with the laminar position in the adult animal. To see whether the cortico-collicular neurons located at various radial levels of layer V are generated concurrently, or whether they follow an "inside-out" pattern of positioning, we divided layer V into three (upper, middle and lower) sublaminae. Most cortico-collicular neurons located in the lower two-thirds of layer V are generated on GD 15 (65%), whereas the neurons located in the upper third of the layer are generated both on GD 15 and GD 16 in almost equal proportions (52.53% and 44.39%, respectively).

Oxiracetam prevents the hippocampal cholinergic hypofunction induced by the NMDA receptor blocker AP7

The intracerebroventricular injection of the N-methyl-D-aspartate (NMDA) receptor antagonist D,L-2-amino-7-phosphonoheptanoic acid (AP7) induces an increase of the hippocampal levels of acetylcholine (ACh) which is dose-dependent in the range 1.5-10 micrograms. Similar doses of AP7 failed to affect the ACh content of the striatum. The effect of the i.c.v. administration of 3.5 micrograms AP7 on hippocampal ACh levels was prevented by pretreatment with oxiracetam 100 mg/kg i.p. In the passive avoidance test the i.c.v. administration of 3.5 micrograms of AP7 caused severe amnesia which was antagonized in a dose-dependent manner by the pretreatment with oxiracetam. These results show that oxiracetam prevents the imbalance of cholinergic activity and the amnesia caused by blockade of NMDA receptors. The present study suggests that the hippocampal cholinergic activity is modulated by glutamatergic neuronal pathways and that the functional integrity of both systems is essential for learning and memory processes.