Monosynaptic inhibitory postsynaptic potentials from lateral habenula recorded in dorsal raphe neurons

The inhibitory response evoked in presumably serotonergic dorsal raphe neurons by stimulation of the lateral habenular nucleus was examined in the rat using intracellular recording techniques. Electrical stimulation of the lateral habenula produces a long-lasting hyperpolarization in dorsal raphe neurons having the slow spontaneous firing pattern (0.5-1.5 spikes/sec) and broad action potential (greater than 1 msec) indicative of serotonergic neurons. The hyperpolarizing response is reversed by hyperpolarizing current injection or by increasing intracellular Cl-concentration and is thus an inhibitory postsynaptic potential (IPSP) due to conductance increase to Cl-. The mean latency of the IPSP is 7.0 msec, which implies a mean conduction velocity for habenulo-raphe axons of 1.2 m/sec. The latency of the response could be demonstrated to be unaffected by changes in stimulus strength, indicating that the IPSP is monosynaptic, which is in agreement with recent anatomical data. Intracellular horseradish peroxidase labeling of responding neurons shows them to have a morphology typical of serotonergic dorsal raphe neurons.     

Valproate enhances inhibitory postsynaptic potentials in hippocampal neurons in vitro

Effects of sodium valproate (0.5-10 mM) on hippocampal cells (CA3 pyramidal cells and granule cells) of the guinea pig in vitro were studied by intra- and extracellular recording. Inhibitory postsynaptic potentials were markedly and reversibly augmented. Their shunting action as well as duration increased by more than 150%. Effects of locally administered gamma-aminobutyric acid (GABA) did not change significantly. Membrane characteristics such as membrane potential, membrane input resistance and action potential did not alter. Valproate suppressed spontaneous spiking and repetitive discharges evoked by GABA antagonists. It is concluded that valproate enhances GABAergic synaptic transmission by a presynaptic mechanism. However, postsynaptic mechanisms might be involved in the limitation of repetitive firing.     

Monosynaptic inputs to ErbB4-expressing inhibitory neurons in mouse primary somatosensory cortex

Previous reports have described inputs to the somatosensory cortex (S1) in mouse or rat using retrograde or anterograde tracers. Such studies do not, however, reveal which particular cell types within the S1 cortex receive direct monosynaptic connections from these input sources. Here we describe the monosynaptic inputs to a subpopulation of mouse S1 inhibitory neurons that express ErbB4. We used a previously described "bridge protein," composed of the ErbB4 ligand, neuregulin (NRG1), fused to the avian viral receptor TVB (TVB-NRG1), along with EnvB pseudotyped lentivirus (LV) and rabies virus (RV), to selectively coinfect ErbB4-expressing neurons (Choi et al. [2010] Proc Natl Acad Sci U S A 107:16703-16708). The RV had its glycoprotein gene deleted and replaced with mCherry, so that infected cells express mCherry and the virus cannot spread without provision of rabies glycoprotein (RG) by transcomplementation. The LV encoded and expressed RG to allow transcomplementation in coinfected neurons, so that the RV could spread transsynaptically and label their direct monosynaptic inputs. The RV could not spread beyond the direct inputs, due to the lack of RG in presynaptic cells. This method revealed long-range connections from thalamus, nucleus basalis, raphe, and distant cortical areas, including ipsilateral motor, secondary somatosensory, retrosplenial, and perirhinal cortex and contralateral S1. In addition, local connections from ipsilateral pyramidal neurons within S1 were labeled. These input sources account for all of the known inputs to S1 described with standard tracers, suggesting that the subpopulation of ErbB4-positive inhibitory neurons infected using the TVB-NRG1 bridge protein receives inputs indiscriminately from S1 input sources.     

A subset of local interneurons generate slow inhibitory postsynaptic potentials in hippocampal neurons

Topical application of 4-aminopyridine (4-AP) onto hippocampal slices produced spontaneous repetitive large hyperpolarizing potentials in CA1 neurons. This effect of 4-AP was blocked by a new GABAB receptor antagonist, 2-hydroxy-saclofen. 2-Hydroxy-saclofen also blocked slow IPSPs evoked by stimulation of stratum radiatum. It is suggested that 4-AP-evoked slow hyperpolarizing potentials are in fact slow IPSPs evoked by activation of a selective subset of interneurons which do not produce fast IPSPs.     

Repetitive inhibitory postsynaptic potentials evoked by 4-aminopyridine in hippocampal neurons in vitro

The effects of topical application of microdrops containing 4-aminopyridine (4-AP) on properties of CA₁ neurons were examined in the hippocampal slice preparation. 4-AP triggered repetitive large (4–10 mV) hyperpolarizing potentials (HPs) having a short rise time and slow (3–4 s) decay. There was a marked decrease in input resistance during the HPs. The HPs are likely to be caused by an increase in potassium conductance; their reversal potential was 15–20 mV negative to rest, the reversal potential shifted in the depolarizing direction when the slice was bathed in high potassium medium, and it was the same with KCl or potassium acetate recording electrodes. The HPs were not generated by release of neurotransmitter substances from terminals of extrinsic afferents since they were present in slices taken from deafferented hippocampus but they were blocked by tetrodotoxin (TTX) or Cd and Mn, indicating that they are synaptic potentials of local origin. HPs were still present when Ca-dependent K currents were blocked by acetylcholine and noradrenaline. Three of 56 cells recorded in the hippocampus could be classified as interneurons. They emitted high frequency trains of action potentials in response to 4-AP, at a rate corresponding to the HPs recorded in all other neurons. It is suggested that 4-AP excites a specific type of interneuron which in turn generates large K-mediated inhibitory postsynaptic potentials in the pyramidal neurons of CA₁ region of the hippocampus.     

Strychnine-induced changes of the membrane and postsynaptic potentials in neocortical neurons]

Intracellular responses of neurons of the suprasylvian gyrus to the intracortical stimulation (ICS) before and after superficial application of strychnine were investigated in experiments on immobilized and unanaesthetized cats. The normal cortex neurons reacted to ICS by monosynaptic EPSPs followed by IPSPs. Strychnine application triggered the epileptiform activity and appearance in neurons of paroxysmal depolarization shifts of the membrane potential (MP) which were replaced by hyperpolarization potentials. An increase and summation of the latter elicited the MP enlargement and either reduction or suppression of background spike activity. Intracellular injections of EGTA blocking the membrane calcium-dependent potassium conductivity (gK(Ca)) have eliminated the hyperpolarization potentials. Development of epileptiform activity was accompanied by depression of IPSPs and increase of the monosynaptic EPSPs. The contribution of gK(Ca) and of postsynaptic inhibition to the epileptogenesis is discussed.     

Fast inhibitory postsynaptic potentials and responses to inhibitory amino acids of sympathetic preganglionic neurons in the adult cat.

Intracellular recordings were obtained from sympathetic preganglionic neurons (SPNs) of the intermediolateral nucleus (IML) in slices of upper thoracic spinal cord of the anesthetized cat. A total of 44 neurons was studied. Single shock stimulation of an area of white matter dorsolateral to the IML, close to the recording electrode (< 0.5 mm), evoked fast IPSPs with rise time of 3.8 ms and 1/2 decay time of 14.7 ms (n = 12). In 17 other cells only fast EPSPs were recorded but, after suppression of the EPSPs by the excitatory amino acid receptor antagonists CNQX (20 microM) and APV (100-250 microM), fast IPSPs were unmasked. The IPSP reversed polarity at -63 mV (-67 mV in the presence of CNQX and APV). The reversal potential shifted to a less negative value when the extracellular chloride concentration was reduced. The IPSP was reversibly abolished by the GABAA receptor antagonist bicuculline in 32% of the cells, by the glycine receptor antagonist strychnine in 47% of the cells and by the combination of the two in 21% of the cells. The IPSP was abolished by TTX (0.5 microM), had constant latency and showed no failures during high frequency stimulation. The IPSP presumably resulted from the excitation of inhibitory axons and/or inhibitory neuron somata with monosynaptic connections to the SPN. Glycine and GABA (1-3 mM) produced hyperpolarization associated with decreased membrane resistance. Sixty-nine percent of cells responded to both agonists, 19% to glycine only and 12% to GABA only. The GABAB agonist baclofen (5 microM) had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)     

Quantum analysis of postsynaptic potentials]

Basic formulations of the quantum theory for synaptic transmission are listed. Methods for determining the mean quantum content, quantum value and binomial parameters describing the amplitude distributions of the unitary and "minimal" postsynaptic potentials are discussed. Literature and author's determinations of the quantum parameters for the synapses of the central nervous system are described. The comparison is made with similar determinations for more studied peripheral junctions. Some difficulties and perspective of the quantum theory are discussed.     

Impulse activity of cultured rat cerebral cortex neurons]

Background spike activity and morphological characteristics of the visual cortex neurons 1-2 day old rats were investigated under conditions of long-term (up to 34 days) tissue cultures. Three types of unit activity were found: single (regular) spikes, bursts and group discharges. Background activity is shown to depend on the cultivation period. Regular firing of neurons for the first 7-15 cultivation days is changed later by bursts or group activity. These changes in neuronal activity coincide in time with the process of morphological maturation of synaptic connections. Strychnine caused a distinct increase in the mean frequency of background activity accompanied by separate series of group discharges. On the basis of the data obtained the problem on the genesis of the spontaneous activity in cortical neurons is discussed.     

Effect of strychnine on evoked potentials and postsynaptic responses of sensomotor cortex neurons in the cat

In acute experiments on cats under light nembutal anaesthesia, immobilized by myorelaxants, superficial application of strychnine was shown to suppress the slow negative potentials (arising during direct and primary cortical responses) and IPSPs of the pyramidal neurons corresponding to the slow negative potentials. Iontophoretic application of strychnine blocks predominantly the early component of IPSP during which the input resistance is significantly less than that of the late component indicating their different genesis. It is concluded that individual components of evoked potentials have a common genesis, the slow negative potential is the reflection of the IPSP of pyramidal neurons whose early component seems to be generated by axo-somatic synapses while the late one by axo-dendritic inhibitory synapses. Neurotransmitters in these inhibitory synapses may be different.     

Selective loss of inhibitory neurons in the cerebral cortex in motor neuron disease

Introduction:  The pattern of β-amyloid (Aβ) deposition in cerebral amyloid angiopathy (CAA) in Alzheimer's disease (AD) suggests that Aβ is eliminated along perivascular interstitial fluid drainage pathways. The age at which accumulation of Aβ in the brain becomes significant in AD coincides with the development of cerebrovascular disease (CVD) and increasing rigidity of artery walls through arteriosclerosis.
Hypothesis:  The distribution of Aβ deposits in Alzheimer brains is influenced by CVD.
Materials and methods:  Paraffin sections of frontal, parietal, temporal and occipital lobes from six cases with Alzheimer's disease were stained for reticulin and by immunocytochemistry for Aβ and GFAP.
Results:  Three distinct patterns of Aβ deposition were seen in relation to cortical blood vessels: (i) early deposition of Aβ in cortical parenchyma was related to individual cortical arterial territories; (ii) severe capillary amyloid angiopathy and an absence of Aβ plaques were associated with thromboembolic occlusion of the feeding artery; (iii) Aβ plaques were abundant in areas devoid of capillary amyloid angiopathy.
Conclusions:  The pattern of Aβ deposition corresponds to individual intracortical arterial territories, and hence periarterial ISF drainage territories. Cerebrovascular disease influences the pattern of Aβ deposition within brain parenchyma and in vessel walls in individual arterial territories. Failure of periarterial drainage of Aβ from the brain may be related to cerebrovascular disease and is possibly due to altered arterial pulsations.     

Dendritic action potentials of pyramidal neurons of the sensomotor cortex of the cerebral cortex of the cat

The intracellular activity of pyramidal tract neurons during electrical stimulation of ventro-lateral and ventro-postero-lateral nuclei of thalamus was studied in acute experiments on cats immobilized by myorelaxants. Both somatic and presumably dendritic spikes (d-spikes) were observed. The latter were characterized by relatively low and variable (5-60 mV) amplitude; d-spikes occurred both spontaneously and in response to single shock and tetanic (8-14/s) stimulation of the thalamus. They were also induced by intracellular depolarizing current pulses and thalamic stimulation following iontophoretic application of strychnine. Simultaneously generated somatic and d-spikes revealed no collision between each other. Intracellular hyperpolarizing current pulses abolished only somatic spikes, while d-spikes were not affected. Dendritic origin with multiple generation zones of these variable spikes is suggested. Possible functional role of d-spike is discussed.     

Lingually induced inhibitory postsynaptic potentials in hypoglossal motoneurons after axotomy

Inhibitory postsynaptic potentials (IPSPs) produced in axotomized hypoglossal motoneurons by stimulation of the lingual nerve were explored in cats. In the ipsilateral lingual afferent synapses, the effectiveness of inhibitory synapses for the long-lasting IPSP was diminished in axotomized hypoglossal motoneurons earlier after transection of the hypoglossal nerves, than the effectiveness of inhibitory synapses for the short-lasting IPSP.     

Dendritic amplification of inhibitory postsynaptic potentials in a model Purkinje cell

In neurons with large dendritic arbors, the postsynaptic potentials interact in a complex manner with active and passive membrane properties, causing not easily predictable transformations during the propagation from synapse to soma. Previous theoretical and experimental studies in both cerebellar Purkinje cells and neocortical pyramidal neurons have shown that voltage-dependent ion channels change the amplitude and time-course of postsynaptic potentials. We investigated the mechanisms involved in the propagation of inhibitory postsynaptic potentials (IPSPs) along active dendrites in a model of the Purkinje cell. The amplitude and time-course of IPSPs recorded at the soma were dependent on the synaptic distance from the soma, as predicted by passive cable theory. We show that the effect of distance on the amplitude and width of the IPSP was significantly reduced by the dendritic ion channels, whereas the rise time was not affected. Somatic IPSPs evoked by the activation of the most distal synapses were up to six times amplified owing to the presence of voltage-gated channels and the IPSP width became independent of the covered distance. A transient deactivation of the Ca(2+) channels and the Ca(2+)-dependent K(+) channels, triggered by the hyperpolarization following activation of the inhibitory synapse, was found to be responsible for these dynamics. Nevertheless, the position of activated synapses had a marked effect on the Purkinje cell firing pattern, making stellate cells and basket cells most suitable for controlling the firing rate and spike timing, respectively, of their target Purkinje cells.     

Novel strategy to selectively label excitatory and inhibitory neurons in the cerebral cortex of mice

Revealing the connections of neuronal systems is critical for understanding how they function. The vast majority of neurons in all cortical areas consist of excitatory cells whose activity is controlled by inhibitory cells. Distribution and projection patterns of inhibitory and excitatory cells are key information to understand the organization of the nervous system. To investigate axonal projections, we developed a method to uniquely distinguish excitatory axons from inhibitory ones in the cortex using transgenic mice expressing Cre recombinase in the Ca2+/calmodulin-dependent protein kinase IIalpha-containing neurons. These animals were injected by an adenoviral vector engineered so that it directs red fluorescent protein expression in non-Cre-expressing cells, and green fluorescent protein in Cre-positive neurons. We demonstrated in vitro and in vivo that GFP-expressing neurons are GABA-immunonegative (excitatory), while the RFP-expressing cells are either GABAergic neurons or glial cells. One week after the viral vector injection RFP and GFP signals overlapped in a subset of cells but after 1 month, the two signals showed total segregation. Six months post-inoculation, GFP-labelling was clearly visible in axons but RFP remained only in somata and proximal dendrites. This technique can thus be used to differentiate excitatory axonal projections from inhibitory ones, and represent a unique tool in neuronal circuit analysis.     

Prolonged depolarizing potentials of the neurons in a strychninized isolated strip of the cat cerebral cortex

Reactions of isolated cortical slab neurons to the supracortical application of strychnine were investigated with intracellular registration in experiments on unanaesthetized and immobilized cats. It was shown that some neurons demonstrated prolonged depolarizing potentials (PDP) spontaneously and as reactions to single intracortical electrical stimuli. The development of these potentials could be a result of transformation of the reaction of the "paroxysmal depolarizing shift (PDS)--hyperpolarization" type, where hyperpolarizations were replaced by depolarizing potentials. A gradual increase of depolarizing afterpotentials resulted in DDP generation. These transformations, as a rule, were accompanied by amplification of the summary epileptiform activity in an isolated cortical slab. The suggestion was made that the DDP generation was determined by an increase in the Ca(++)-conductance of the neuronal membrane in an isolated cortical slab with the intensification of paroxysmal reactions.     

SAP97 concentrates at the postsynaptic density in cerebral cortex

SAP97, a PDZ-containing protein, is reported to concentrate in axon terminals, where its function remains unknown. Using highly specific new antibodies, we show that SAP97 in rat cerebral cortex is associated with heteromeric AMPA receptors via a selective biochemical interaction between SAP97 and the GluR1 subunit. Using light and electron microscopic immunocytochemistry, we demonstrate cellular and synaptic colocalization of SAP97 and GluR1, and show that SAP97 concentrates at synapses that contain GluR1 but not necessarily GluR2 or GluR3. Using quantitative postembedding immunogold electron microscopy, we find that SAP97 is at highest concentration within the postsynaptic density of asymmetric synapses. These data suggest that SAP97 may help to anchor GluR1-containing AMPA receptors at the synapse. As a multifunctional scaffolding protein, SAP97 may organize components of AMPA-related intracellular signalling pathways, including those associated with calcium-permeable homomeric GluR1 channels.