Cortical Pyramidal Cells Research Articles

Strong Single-Fiber Sensory Inputs to Olfactory Cortex: Implications for Olfactory Coding

Olfactory information is first encoded in a combinatorial fashion by olfactory bulb glomeruli, which individually represent distinct chemical features of odors. This information is then transmitted to piriform (olfactory) cortex, via axons of olfactory bulb mitral and tufted (M/T) cells, where it is presumed to form the odor percept. However, mechanisms governing the integration of sensory information in mammalian olfactory cortex are unclear. Here we show that single M/T cells can make powerful connections with cortical pyramidal cells, and coincident input from few M/T cells is sufficient to elicit spike output. These findings suggest that odor coding is broad and distributed in olfactory cortex.

The Effects of Morphine Self-Administration on Cortical Pyramidal Cell Structure in Addiction-Prone Lewis Rats

The consumption of drugs of abuse provokes sensitization, the development of tolerance, dependency, and eventually addiction. It is thought that these events are partially a consequence of drug-induced alterations in the organization of neuronal circuits in specific areas of the brain. In the present study, we have used intracellular injections of lucifer yellow to examine the alterations that may occur in cortical pyramidal neurons of addiction-prone Lewis rats following 15 days of self-administration of morphine. Specifically, the effects of morphine on the structure, size and branching complexity of the basal dendrites, and spine density were determined in the basal dendritic arbors of layer III pyramidal neurons in both the prelimbic and motor cortex. We found that following morphine self-administration, there was a reduction in the size and branching complexity of the dendritic arbors of pyramidal cells in the motor cortex. In contrast, prelimbic pyramidal neurons from these morphine-treated animals had larger and longer basal dendritic arbors. Furthermore, the spine density on pyramidal neurons was higher in both cortical regions of morphine self-administered rats. These results suggest that at least part of the behavioral changes produced by repeated opiate administration may be attributed to alterations in pyramidal cell structure.

Effect of cortical spreading depression on basal forebrain neurons

During natural sleep and anesthesia, rhythmic hypo- and hyperpolarizations alternate in cortical pyramidal cells and are reflected as slow (<1 Hz) cortical rhythm at the level of the electroencephalogram (EEG). Membrane potential changes in pyramidal neurons were initially attributed to the rhythmic fluctuation of the cholinergic input as the basal forebrain (BF) neurons fire in synchrony with cortical waves, but a more recent proposal suggested that the slow rhythm was of cortical origin. In the present experiments, interaction between the cortex and the BF was examined in urethane-anesthetized rats. BF neuronal activity was inhibited by local infusion of lidocaine into the substantia innominata in one group of rats, while in another group, the slow cortical rhythm was blocked by inducing spreading depression (SD) in the cortex. Slow cortical rhythm persisted after unilateral lidocaine injection, but rhythmic firing in BF neurons disappeared following SD induction. These findings support the view that slow cortical rhythm is generated in the cortex and transmitted to the BF through descending fibers. According to anatomical data, these fibers can excite cholinergic cells only indirectly as they terminate on non-cholinergic neurons. Thus, timing of activity changes in BF neurons during the slow cortical rhythm might give some clue regarding their transmitter specificity.

Axonal Growth and Guidance Defects inFrizzled3Knock-Out Mice: A Comparison of Diffusion Tensor Magnetic Resonance Imaging, Neurofilament Staining, and Genetically Directed Cell Labeling

Previous work has identified axonal outgrowth and/or guidance defects in the brain and spinal cord of prenatal Frizzled3 (Fz3)(-/-) mice. To systematically explore the axonal defects in Fz3(-/-) mice and to compare techniques for the global assessment of axon tracts in the developing mouse, we have analyzed wild-type and Fz3(-/-) brains using (1) diffusion tensor magnetic resonance imaging (muDTI), (2) neurofilament staining, and (3) two genetically directed neuronal labeling methods. Confirming and extending the previous work of Wang et al. (2002), we find that the following structures/tracts are absent or greatly reduced in the Fz3(-/-) brain: the anterior commissure, cerebral peduncle (corticospinal tract), corpus callosum, fornix, internal capsule (thalamocortical and corticothalamic tracts), stria medullaris, stria terminalis, and hippocampal commissure. An aberrant U-shaped fiber bundle immediately caudal to the optic tract connects the left and right sides of the Fz3(-/-) thalamus and likely represents a default pathway for thalamic axons that failed to enter the internal capsule. At embryonic day 18, labeling of cortical pyramidal cells with a yellow fluorescent protein reporter reveals widespread fragmentation of axons with no apparent loss of pyramidal cell bodies. Fragmentation likely represents one stage in the process that normally eliminates stalled or mistargeted axons. This work demonstrates the usefulness of muDTI and genetically directed neuronal labeling for the analysis of nervous system defects in the mouse.

Mapping Cortical Activity Elicited with Electrical Microstimulation Using fMRI in the Macaque

Over the last two centuries, electrical microstimulation has been used to demonstrate causal links between neural activity and specific behaviors and cognitive functions. However, to establish these links it is imperative to characterize the cortical activity patterns that are elicited by stimulation locally around the electrode and in other functionally connected areas. We have developed a technique to record brain activity using the blood oxygen level dependent (BOLD) signal while applying electrical microstimulation to the primate brain. We find that the spread of activity around the electrode tip in macaque area V1 was larger than expected from calculations based on passive spread of current and therefore may reflect functional spread by way of horizontal connections. Consistent with this functional transynaptic spread we also obtained activation in expected projection sites in extrastriate visual areas, demonstrating the utility of our technique in uncovering in vivo functional connectivity maps.

CYP2B6 is expressed in African Green monkey brain and is induced by chronic nicotine treatment

CYP2B6 is a drug-metabolizing enzyme expressed in human tissues that can activate bupropion (a smoking cessation drug) and tobacco smoke nitrosamines and can inactivate drugs such as nicotine. Smokers have higher brain CYP2B6 protein levels compared to non-smokers but the cause of this elevation is unknown. We investigated the basal expression and the effect of chronic nicotine treatment on CYP2B6 protein in African Green monkey ( Cercopithecus aethiops) brain. Basal expression of brain CYP2B6 was strong in specific cells such as the frontal cortical pyramidal cells, the cerebellar Purkinje cells and the neurons in the substantia nigra. Basal CYP2B6 protein levels varied 2.7-fold (non-significant) among 12 brain regions. All monkeys were given a subcutaneous 0.1 mg/kg nicotine test dose prior to treatment and the maximum plasma concentration achieved was 87 ± 69 ng/ml and the half-life was 2.6 ± 1.5 h. Monkeys were treated subcutaneously twice daily with nicotine at 0.05 mg/kg for 2 days, 0.15 mg/kg for 2 days followed by 0.3 mg/kg for 18 days ( n = 6) or saline ( n = 6). Chronic nicotine treatment induced CYP2B6 expression in specific cells such as astrocytes and neurons in the frontal cortex, caudate, thalamus and hippocampus. CYP2B6 protein levels were induced 1.5-fold in the frontal cortex ( p < 0.01). Hepatic CYP2B6 expression was not altered by nicotine. In conclusion, CYP2B6 protein is expressed in specific cells in monkey brain and is induced by chronic nicotine treatment which may impact central metabolism of CYP2B6 substrates such as bupropion and nicotine.

Inhibitory Postsynaptic Potentials Carry Synchronized Frequency Information in Active Cortical Networks

Temporal precision in spike timing is important in cortical function, interactions, and plasticity. We found that, during periods of recurrent network activity (UP states), cortical pyramidal cells in vivo and in vitro receive strong barrages of both excitatory and inhibitory postsynaptic potentials, with the inhibitory potentials showing much higher power at all frequencies above approximately 10 Hz and more synchrony between nearby neurons. Fast-spiking inhibitory interneurons discharged strongly in relation to higher-frequency oscillations in the field potential in vivo and possess membrane, synaptic, and action potential properties that are advantageous for transmission of higher-frequency activity. Intracellular injection of synaptic conductances having the characteristics of the recorded EPSPs and IPSPs reveal that IPSPs are important in controlling the timing and probability of action potential generation in pyramidal cells. Our results support the hypothesis that inhibitory networks are largely responsible for the dissemination of higher-frequency activity in cortex.

Gap-Junctional Coupling between Neurogliaform Cells and Various Interneuron Types in the Neocortex

Electrical synapses contribute to the generation of synchronous activity in neuronal networks. Several types of cortical GABAergic neurons acting via postsynaptic GABA(A) receptors also form electrical synapses with interneurons of the same class, suggesting that synchronization through gap junctions could be limited to homogenous interneuron populations. Neurogliaform cells elicit combined GABA(A) and GABA(B) receptor-mediated postsynaptic responses in cortical pyramidal cells, but it is not clear whether neurogliaform cells are involved in networks linked by electrical coupling. We recorded from pairs, triplets, and quadruplets of cortical neurons in layers 2 and 3 of rat somatosensory cortex (postnatal day 20-35). Neurogliaform cells eliciting slow IPSPs on pyramidal cells also triggered divergent electrical coupling potentials on interneurons. Neurogliaform cells were electrically coupled to other neurogliaform cells, basket cells, regular-spiking nonpyramidal cells, to an axoaxonic cell, and to various unclassified interneurons showing diverse firing patterns and morphology. Electrical interactions were mediated by one or two electron microscopically verified gap junctions linking the somatodendritic domain of the coupled cells. Our results suggest that neurogliaform cells have a unique position in the cortical circuit. Apart from eliciting combined GABA(A) and GABA(B) receptor-mediated inhibition on pyramidal cells, neurogliaform cells establish electrical synapses and link multiple networks formed by gap junctions restricted to a particular class of interneuron. Widespread electrical connections might enable neurogliaform cells to monitor the activity of different interneurons acting on GABA(A) receptors at various regions of target cells.

Neural Cell Adhesion Molecule-Secreting Transgenic Mice Display Abnormalities in GABAergic Interneurons and Alterations in Behavior

The extracellular region of the transmembrane neural cell adhesion molecule (NCAM-EC) is shed as a soluble fragment at elevated levels in the schizophrenic brain. A novel transgenic mouse line was generated to identify consequences on cortical development and function of expressing soluble NCAM-EC from the neuron-specific enolase promoter in the developing and mature neocortex and hippocampus. NCAM-EC transgenic mice exhibited a striking reduction in synaptic puncta of GABAergic interneurons in the cingulate, frontal association cortex, and amygdala but not hippocampus, as shown by decreased immunolabeling of glutamic acid decarboxylase-65 (GAD65), GAD67, and GABA transporter 1. Interneuron cell density was unaltered in the transgenic mice. Affected subpopulations of interneurons included basket interneurons evident in NCAM-EC transgenic mice intercrossed with a reporter line expressing green fluorescent protein and by parvalbumin staining. In addition, there appeared to be a reduction in excitatory synapses, as revealed by synaptophysin staining and apical dendritic spine density of cortical pyramidal cells. Behavioral analyses demonstrated higher basal locomotor activity of NCAM-EC mice and enhanced responses to amphetamine and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate compared with wild-type controls. Transgenic mice were deficient in prepulse inhibition, which was restored by clozapine but not by haloperidol. Additionally, NCAM-EC mice were impaired in contextual and cued fear conditioning. These results suggested that elevated shedding of NCAM perturbs synaptic connectivity of GABAergic interneurons and produces abnormal behaviors that may be relevant to schizophrenia and other neuropsychiatric disorders.

Cortical Development: New Concepts

Cortical Development: New Concepts

Areal specialization of pyramidal cell structure in the visual cortex of the tree shrew: a new twist revealed in the evolution of cortical circuitry

Cortical pyramidal cells, while having a characteristic morphology, show marked phenotypic variation in primates. Differences have been reported in their size, branching structure and spine density between cortical areas. In particular, there is a systematic increase in the complexity of the structure of pyramidal cells with anterior progression through occipito-temporal cortical visual areas. These differences reflect area-specific specializations in cortical circuitry, which are believed to be important for visual processing. However, it remains unknown as to whether these regional specializations in pyramidal cell structure are restricted to primates. Here we investigated pyramidal cell structure in the visual cortex of the tree shrew, including the primary (V1), second (V2) and temporal dorsal (TD) areas. As in primates, there was a trend for more complex branching structure with anterior progression through visual areas in the tree shrew. However, contrary to the trend reported in primates, cells in the tree shrew tended to become smaller with anterior progression through V1, V2 and TD. In addition, pyramidal cells in V1 of the tree shrew are more than twice as spinous as those in primates. These data suggest that variables that shape the structure of adult cortical pyramidal cells differ among species.

Learning temporal clusters with synaptic facilitation and lateral inhibition

Short-term synaptic plasticity has been proposed as a way for cortical neurons to process temporal information. We present a model network that uses short-term plasticity to implement a temporal clustering algorithm. The model's facilitory synapses learn temporal signals drawn from mixtures of nonlinear processes. Units in the model correspond to populations of cortical pyramidal cells arranged in columns; each column consists of neurons with similar spatiotemporal receptive fields. Clustering is based on mutual inhibition similar to Kohonen's SOMs. A generalized expectation maximization (GEM) algorithm, guaranteed to increase model likelihood with each iteration, learns the synaptic parameters.

Immunohistochemical localization of the amino acid transporter SNAT2 in the rat brain

SNAT2 is a neutral amino acid carrier that belongs to the system A family. Since its function in the nervous system remains unclear, we have analyzed its distribution in the rat CNS using specific antisera. Although SNAT2 is expressed widely in the CNS, it is enriched in the spinal cord and the brainstem nuclei, especially those of the auditory system. At the cellular level, SNAT2 was preferentially located in neuronal cell bodies and processes, although it was also strongly expressed in the meninges and ependyma. In astrocytes, the localization of SNAT2 was more restricted since it was intensely expressed in the perivascular end-feet, glia limitans, cerebellar astrocytes and Bergmann glia, but it was less intense in astrocytes of the cerebral parenchyma. Among neurons, the primary sensory neurons of the mesencephalic trigeminal nucleus appeared to be those that most strongly express SNAT2, but many other neurons, including cortical pyramidal cells and their dendrites were also intensely stained. In several regions the transporter was detected in axons, especially in the brainstem, and its presence in both dendrites and axons was confirmed by confocal microscopy and ultrastructural studies. However, while SNAT2 was observed in the large principal dendrites and the small distal dendrites, it was only found in axonal shafts and was excluded from terminals. Some glutamatergic neurons were among the more intensely labeled cells whereas SNAT2 was not detected on GABAergic neurons. The expression of SNAT2 partially coincides with that reported for SNAT1, especially in glutamatergic neurons. Hence, both proteins could fulfill complementary roles in replenishing glutamate pools and be differentially regulated under different physiological conditions. They also seem to co-localize in non-neuronal cells probably contributing to amino acid fluxes through the blood–brain barrier.

Dopamine-glutamate interactions controlling prefrontal cortical pyramidal cell excitability involve multiple signaling mechanisms.

Although the importance of dopamine (DA) for prefrontal cortical (PFC) cognitive functions is widely recognized, the nature of DA actions in the PFC remains controversial. A critical component in DA actions is its modulation of glutamate transmission, which can be different when specific receptors are activated. To obtain a clear picture of cellular mechanisms involved in these interactions, we studied the effects of DA-glutamate coactivation on pyramidal cell excitability in brain slices obtained from developmentally mature rats using whole-cell patch-clamp recordings. Bath application of NMDA, AMPA, and the D1 agonist SKF38393 induced concentration-dependent excitability increases, whereas bath application of the D2 receptor agonist quinpirole induced a concentration-dependent excitability decrease. The NMDA-mediated response was potentiated by SKF38393. This NMDA-D1 synergism required postsynaptic intracellular Ca2+ and protein kinase A (PKA) and was independent of membrane depolarization. On the other hand, the excitatory effects of both NMDA and AMPA were attenuated by a D2 agonist. Surprisingly, the D2-NMDA interaction was also blocked by the GABA(A) antagonists bicuculline and picrotoxin, suggesting that the inhibitory action of D2 receptors on NMDA-induced responses in the PFC may be mediated by GABAergic interneurons. In contrast, the D2-AMPA interaction involves inhibition of PKA and activation of phospholipase lipase C-IP3 and intracellular Ca2+ at a postsynaptic level. Thus, the modulatory actions of D1 and D2 receptors on PFC pyramidal cell excitability are mediated by multiple intracellular mechanisms and by activation of GABA(A) receptors, depending on the glutamate receptor subtypes involved.

Cellular distribution of the endothelin system in the human brain

The vasoconstrictor endothelin-1 (ET-1) may also act as a neuropeptide. ET-1 is formed by the catalytic action of endothelin-converting enzyme-1 (ECE-1) on big ET-1 and its cellular actions are mediated via ET A and ET B receptors. Although localisation of these components in rodent brain has been extensively investigated, no single study has mapped their distribution in human brain. Here we describe the localisation of ET-1 mRNA, ET-1, ECE-1, ET A and ET B receptors within 24 human brain regions. In situ RT-PCR has previously detected ET-1 mRNA in 22 areas (excluding the post-central gyrus and pineal gland), and ET-1 immunoreactivity was visualised in cells of all regions. Using specific antibodies we have immunolocalised ECE-1 and ET B receptors in cells of 24 areas, and ET A receptors in nine regions (choroidal epithelial cells, neurones in the diencephalon, hippocampus, amygdaloid, dentate nucleus, Purkinje cells of the cerebellum, flocculo-nodular lobe and vermis). ET-1 mRNA, ET-1, ECE-1 and ET B receptors were observed in cortical pyramidal cells, neurones (brainstem, basal nuclei, thalamus, insula and claustrum, limbic region), cells in the anterior pituitary gland; nerve cell processes in the pars nervosa; pinealocytes and choroidal epithelial cells. Only ET-1 mRNA, ET-1, ECE-1, and ET B receptors were visualised in cerebral capillary endothelial cells. The presence of ET-1 mRNA, ECE-1 and ET-1 in 22 brain regions confirms ET expression and processing in human brain. The localisation of ET-1 and ET B receptors suggests receptor-mediated action akin to a neurotransmitter role for ET-1.

Cortical responsiveness is reduced during P300 potential. Does the level of initial activity affect this inhibition?

The regulation of firing thresholds of cortical pyramidal cells has been suggested as one of the mechanisms underlying the generation of the P300 component of the human event-related potential. According to this hypothesis, the detection of an important stimulus produces a widespread inhibition of "irrelevant" networks, interrupting the ongoing cortical activity and facilitating the analysis of the important information. In the present experiment, target stimuli in a standard "odd-ball" paradigm were used as important events. The cortical responsiveness was measured using the responses to additional probing stimuli delivered 400 ms and 1,000 ms after target and non-target stimuli. The subjects were asked to count mentally the target stimuli and ignore the non-targets and the probes. The level of "irrelevant" cortical activity was manipulated using additional visual noise stimulation. Event-related potentials were recorded at Fz, Cz, Pz and Oz scalp sites. Our results showed that the noise reduced the initial responses to target and non-target stimuli in Oz, Pz and Cz but not in Fz recordings. The noise reduced the probe responses in Oz and Pz but not in Cz and Fz recordings. The amplitudes of P300 components were not affected by the noise. The target stimuli reduced the subsequent probe responses in Pz and Cz but not in Oz and Fz recordings. Thus, the effects of noise and target detection were not identical in the different regions of cortex. The other important outcome of our study was that the target stimuli suppressed the effects of noise. The effect of noise on probe responses was significant in the non-target but not in the target trials. The effect of noise was significant if the probes were delivered 1,000 ms after "odd-ball" stimuli, but it was insignificant when the delay was only 400 ms. Such results support the hypothesis that important information reduces cortical responses to other, irrelevant stimuli.

Accelerated dendritic development of rat cortical pyramidal cells and interneurons after biolistic transfection with BDNF and NT4/5.

Neurotrophins are candidate molecules for regulating dendritogenesis. We report here on dendritic growth of rat visual cortex pyramidal and interneurons overexpressing 'brain-derived neurotrophic factor' BDNF and 'neurotrophin 4/5' NT4/5. Neurons in organotypic cultures were transfected with plasmids encoding either 'enhanced green fluorescent protein' EGFP, BDNF/EGFP or NT4/5/EGFP either at the day of birth with analysis at 5 days in vitro, or at 5 days in vitro with analysis at 10 days in vitro. In pyramidal neurons, both TrkB ligands increased dendritic length and number of segments without affecting maximum branch order and number of primary dendrites. In the early time window, only infragranular neurons were responsive. Neurons in layers II/III became responsive to NT4/5, but not BDNF, during the later time window. BDNF and NT4/5 transfectants at 10 days in vitro had still significantly shorter dendrites than adult pyramidal neurons, suggesting a massive growth spurt after 10 days in vitro. However, segment numbers were already in the range of adult neurons. Although this suggested a role for BDNF, long-term activity-deprived, and thus BDNF-deprived, pyramidal cells developed a dendritic complexity not different from neurons in active cultures except for higher spine densities on neurons of layers II/III and VI. Neutralization of endogenous NT4/5 causes shorter and less branched dendrites at 10 days in vitro suggesting an essential role for NT4/5. Neutralization of BDNF had no effect. Transfected multipolar interneurons became identifiable during the second time window. Both TrkB ligands significantly increased number of segments and branch order towards the adult state with little effects on dendritic length. The results suggested that early in development BDNF and NT4/5 probably accelerate dendritogenesis in an autocrine fashion. In particular, branch formation was advanced towards the adult pattern in pyramidal cells and interneurons.

Mechanisms for resin acid effects on membrane currents and GABA A receptors in mammalian CNS

Resin acids from bleached wood pulp are toxic to fish. 12,14-Dichlorodehydroabietic acid (12,14-Cl 2DHA) raises cytoplasmic Ca 2+ in synaptosomes and blocks neural GABA A receptors; however, the underlying mechanism remains unclear in these earlier rodent studies. 12,14-Cl 2DHA (50 μM) almost completely blocked native GABA A currents (rat cortical cultures) but had no significant effect on picrotoxin-sensitive recombinant human receptors in oocytes (α1, β2 and γ2L: the most prevalent isoforms in mammalian brain). In oocytes, 12,14-Cl 2DHA failed to produce a calcium-activated chloride current, in contrast to the calcium ionophore ionomycin (10 μM). However, in cultured cortical pyramidal cells, both ionomycin and 12,14-Cl 2DHA produced chloride-selective currents of similar magnitude (presumably secondary to Ca 2+ release). 12,14-Cl 2DHA was unable to stimulate phosphate labelling of [ 3 H ]-inositol in mouse synaptosomes, indicating that the study compound does not cause Ca 2+ release via an IP 3 mechanism. Calcium pump ATPase inhibition also seems unlikely since thapsigargin did not elevate free calcium in synaptosomes. 12,14-Cl 2DHA clearly blocks GABA A currents indirectly: we infer that its toxicity may be secondary to the elevations in cytoplasmic Ca 2+ via an unidentified recognition site (or receptor) found in neuronal cells.

Histopathology and reorganization of chandelier cells in the human epileptic sclerotic hippocampus.

Impairment of GABA-mediated inhibition is one of the main hypotheses invoked to explain seizure activity, both in experimental models and in human epilepsy. We have studied the distribution and the neurochemical characteristics of certain GABAergic circuits in the normal and epileptic human sclerotic hippocampal formation. We have focused our attention mainly on chandelier cells because, together with basket cells, they are considered to have powerful effects on spike generation. Chandelier cells represent a unique type of interneuron whose axon terminals (Ch-terminals) form synapses with the axon initial segments of cortical pyramidal cells and granular cells of the dentate gyrus. Different neurochemical subpopulations of chandelier cells have been identified by immunocytochemistry, mainly in the neocortex. Markers for Ch-terminals include the GABA transporter 1 (GAT-1), the polysialylated form of the cell-surface glycoprotein neural cell adhesion molecule (PSA-NCAM) and the calcium-binding proteins parvalbumin (PV) and calbindin D-28k (CB). In the normal hippocampal formation, GAT-1- and PV-immunoreactive (-ir) Ch-terminals were identified in the granular and polymorphic layers of the dentate gyrus, in the strata pyramidale and oriens of the CA fields, and in the pyramidal layer of the subicular complex. In addition, and in contrast to the hippocampus and dentate gyrus, subsets of Ch-terminals in the upper pyramidal layer of the normal subiculum express CB and PSA-NCAM. The sclerotic hippocampus of epileptic patients presented an impressive morphological and neurochemical reorganization of Ch-terminals and basket formations. This was apparent in the dentate gyrus and hippocampal formation, but not in the subiculum, which appeared to remain unaltered. Principally, numerous and more complex PV- and CB-ir Ch-terminals, as well as dense PV-ir basket formations, appeared in some hippocampal segments, whereas in other regions there was a lack of labelled elements. These changes varied considerably not only between different patients, but also within different hippocampal fields in a given patient. In general, the changes were not correlated with the clinical characteristics or degree of histopathological alterations observed in the patients, such as granular cell dispersion, neuron loss and proliferation of mossy fibres. However, some surviving neurons in the regions adjacent to the areas of neuron loss were consistently innervated by dense basket formations and complex Ch-terminals. These results indicate that, in the human epileptic hippocampus, GABAergic circuits are more highly modified than previously thought. When considered along with other extrahippocampal alterations, we suggest that these changes are important in the pathophysiology of temporal lobe epilepsy associated with hippocampal sclerosis.

S.08.05 Metabotropic glutamate receptors in the amygdala and fear

Serotonin and norepinephrine, in addition to direct postsynaptic excitatory effects, also enhances glutamate release onto layer V pyramidal cells of the prefrontal cortex/neocortex via Gq/11-coupled 5-hydroxytryptamine2A (5-HT2A) and α1-adrenergic receptors, respectively. Therefore, the present study was designed to test whether a metabotropic glutamate (mGlu) receptor subtype also coupled to Gq/11-proteins, the mGlu5 receptor, also induces EPSCs when recording from layer V cortical pyramidal cells of the rat medial prefrontal cortex (mPFC). The mGlu1/5 receptor agonist (S)-3,5-dihydroxyphenylglycine (DHPG) induces EPSCs at a similar frequency as a near-maximally effective 5-HT concentration. The mGlu5 receptor negative allosteric modulator 2-methyl-6-(phenylethynyl)pyridine (MPEP, 300 nM) potently blocked DHPG-induced EPSCs. Previous work has suggested that activation of 5-HT2A and OX2 receptors induces glutamate release, while mGlu2, mGlu4, and mGlu8 receptor activation suppress transmitter release from thalamocortical terminals. Taken together with past results, these findings suggest that mGlu2, mGlu4, mGlu5 and mGlu8 may all act to modulate glutamate release from afferents impinging on layer V pyramidal cells of the mPFC. These findings further suggest that monoamines, neuropeptides and glutamate itself all enhance the excitability of prefrontal cortical output cells indirectly via modulation of glutamate release.