Active summation of excitatory postsynaptic potentials in hippocampal CA3 pyramidal neurons

The manner in which the thousands of synaptic inputs received by a pyramidal neuron are summed is critical both to our understanding of the computations that may be performed by single neurons and of the codes used by neurons to transmit information. Recent work on pyramidal cell dendrites has shown that subthreshold synaptic inputs are modulated by voltage-dependent channels, raising the possibility that summation of synaptic responses is influenced by the active properties of dendrites. Here, we use somatic and dendritic whole-cell recordings to show that pyramidal cells in hippocampal area CA3 sum distal and proximal excitatory postsynaptic potentials sublinearly and actively, that the degree of nonlinearity depends on the magnitude and timing of the excitatory postsynaptic potentials, and that blockade of transient potassium channels linearizes summation. Nonlinear summation of synaptic inputs could have important implications for the computations performed by single neurons and also for the role of the mossy fiber and perforant path inputs to hippocampal area CA3.     

Projections of submucous neurons to the myenteric plexus in the guinea pig small intestine

Coronary venous hypertension induced by partial coronary sinus obstruction (CSO) in the dog, prevents or delays the predictable ventricular fibrillation (VF) of the early phase of acute ischemia. Also, CSO acting presumably through enhanced myocardial hydration, normalizes the inhomogenous extracellular potassium ([K+]o) accumulation, a major factor in producing the electrophysiological disparities, characteristic of arrhythmogenic substrate. To further clarify the mechanism of early ischemic VF prevention in dogs, radioactive microspheres were used to evaluate regional perfusion changes, resulting from CSO sufficient to raise the coronary sinus pressure to 40 mmHg, before and during ischemia induced by double coronary artery occlusion (CAO) (n=5). Also, global or regional unipolar electrogram mapping was used to assess changes of epicardial ventricular activation times (AT) and sequence and activation recovery intervals (ARI) during CSO, CAO and combined CSO and CAO, induced in random order (n=8). CSO did not affect regional perfusion nor improved collateral blood flow during ischemia. With CSO, AT shortened modestly over time (0.41+/-1.1 ms/min, r=0.85, P<0. 05) and ARI transiently decreased by up to 5.5%. With CAO, AT became variably delayed and isochrone map distortions were indicative of localized conduction delays or blocks, consistent with elevated [K+]o. In contrast, when CAO was preceded by CSO, AT delays were homogenous and normal activation sequence was preserved. Also, whereas with CAO, ARI shortened unequally over the ischemic region by as much as 43% at individual sites (average of 38.3+/-6.8 ms, P<0. 001), with combined CSO and CAO, ARI shortening was less pronounced and more homogenous (26.1+/-5.6 ms, P<0.05), not exceeding 29% at any site. Thus, in accordance with previous findings of enhanced [K+]o homogeneity, coronary venous hypertension reduces the disparities of activation and refractoriness of ischemia attributable, at least in part, to disparate [K+]o accumulation. Since no collateral blood flow improvement could be identified, the salutary electrophysiological effects of CSO may reflect a more homogenous extracellular environment, due to preservation of normal microvascular pressure (Pmv) and sustained filtration and lymph flow.     

Extrinsic denervation increases myenteric nitric oxide synthase-containing neurons and inhibitory neuromuscular transmission in guinea pig

Enteric nerves can function normally without connections with the central nervous system. A contributing component of the functional autonomy exhibited by enteric nerves is their plasticity. In the present study, the number of nitric oxide synthase-immunoreactive (NOS-ir) myenteric neurons and inhibitory neuromuscular transmission were studied in extrinsically denervated ileal segments. Segments of ileum were extrinsically denervated by crushing the mesenteric blood vessels supplying a loop of ileum in anesthetized guinea pigs. Some unoperated animals were treated with capsaicin or 6-hydroxydopamine (6-OHDA) to disrupt primary afferent and sympathetic nerves, respectively. NOS-ir was localized using indirect immunofluorescence. Nerve-mediated relaxations of longitudinal muscle were studied in vitro using standard methods. At 7 weeks after extrinsic denervation there was a 93% increase in the number of NOS-ir myenteric neurons. The number of neurons containing detectable vasoactive intestinal peptide-ir neurons was not changed after extrinsic denervation. Neurogenic relaxations caused by 10, 20 and 50 Hz transmural stimulation were larger in extrinsically-denervated tissues compared to control tissues. The NOS antagonist, nitro-L-arginine (300 microM) inhibited neurogenic relaxations in control and extrinsically-denervated tissues. Capsaicin- but not 6-OHDA-treatment mimicked the effects of extrinsic denervation on NOS-ir and neurogenic relaxations of the longitudinal muscle. Active or passive properties of the longitudinal muscle were unaffected by extrinsic denervation. These data indicate that extrinsic denervation is associated with an increase in the number of myenteric neurons expressing detectable NOS-ir and potentiation of inhibitory transmission to longitudinal muscle. This effect is due to loss of extrinsic sensory nerves.     

Anoxic depression of excitatory and inhibitory postsynaptic potentials in rat neocortical slices

1. The effects of brief anoxia (4-6 min replacement of O2 by N2) on synaptic potentials evoked from layer IV and/or the white matter were studied in pyramidal neurons of layers II-III from rat neocortical slices. 2. The early and late components of excitatory postsynaptic potentials (EPSPs) showed differential sensitivity to anoxia: within 2 min the late EPSP (lEPSP) disappeared, whereas the amplitude of the early EPSP (eEPSP) decreased by 70% at 5 min of anoxia. Recovery was complete within 4-11 min. 3. Both fast and slow inhibitory postsynaptic potentials (IPSPs) were extremely sensitive to lack of O2 and were abolished earlier than the lEPSP evoked by the same stimulus. As well, recovery of the IPSPs was always more delayed than that of the EPSPs. 4. A transient increase in excitability during early anoxia and/or midrecovery, manifested as enhanced probability of spiking in 25% of neurons, is attributed to the higher sensitivity of IPSPs compared with EPSPs. 5. The anoxic-induced depression of the lEPSP and IPSPs, which are generated close to the soma, is not due to depolarization-induced occlusion; however, occlusion may cause an attenuation of the eEPSP at dendritic sites. 6. The depression of the EPSPs is not a result of a decreased transmembrane Na+ gradient after inactivation of Na-K-adenosine triphosphatase (Na-K-ATPase). Although ouabain induced a depolarization similar to that of anoxia, it did not affect EPSP amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serotonin induces excitatory postsynaptic potentials in apical dendrites of neocortical pyramidal cells

By intracellular and whole cell recording in rat brain slices, it was found that bath-applied serotonin (5-HT) produces an increase in the frequency and amplitude of spontaneous excitatory postsynaptic potentials/currents (EPSPs/EPSCs) in layer V pyramidal cells of neocortex and transitional cortex (e.g. medial prefrontal, cigulate and frontoparietal). The EPSCs were suppressed by LY293558, an antagonist selective for the AMPA subtype of excitatory amino acid receptor, and by two selective 5-HT2A receptor antagonists, MDL 100907 and SR 46349B. In addition, the EPSCs were suppressed by the fast sodium channel blocker tetrodotoxin (TTX) and were dependent upon external calcium. However, despite being TTX-sensitive and calcium dependent, there was no evidence that the EPSPs resulted from an increase in impulse flow in excitatory neuronal afferents to layer V pyramidal cells. The EPSCs could be induced rapidly by the microiontophoresis of 5-HT directly to "hot spots" within the apical (but not basilar) dendritic field of recorded neurons, indicating that excitatory amino acids may be released by a TTX-sensitive focal action of 5-HT on a subset of glutamatergic terminals in this region. Consistent with such a presynaptic action, the inhibitory metabotropic glutamate receptor agonist (1S,3S)-aminocyclopentane-1,3-dicarboxylate markedly reduced the induction of EPSPs by 5-HT. Postsynaptically, 5-HT enhanced a subthreshold TTX-sensitive sodium current, potentially contributing to an amplification of EPSC amplitudes. These data suggest 5-HT. via 5-HT2A receptors, enhances spontaneous EPSPs/EPSCs in neocortical layer V pyramidal cells through a TTX-sensitive focal action in the apical dendritic field which may involve both pre- and postsynaptic mechanisms.     

Calcium dynamics in single spines during coincident pre- and postsynaptic activity depend on relative timing of back-propagating action potentials and subthreshold excitatory postsynaptic potentials

We compared the transient increase of Ca2+ in single spines on basal dendrites of rat neocortical layer 5 pyramidal neurons evoked by subthreshold excitatory postsynaptic potentials (EPSPs) and back-propagating action potentials (APs) by using calcium fluorescence imaging. AP-evoked Ca2+ transients were detected in both the spines and in the adjacent dendritic shaft, whereas Ca2+ transients evoked by single EPSPs were largely restricted to a single active spine head. Calcium transients elicited in the active spines by a single AP or EPSP, in spines up to 80 micro(m) for the soma, were of comparable amplitude. The Ca2+ transient in an active spine evoked by pairing an EPSP and a back-propagating AP separated by a time interval of 50 ms was larger if the AP followed the EPSP than if it preceded it. This difference reflected supra- and sublinear summation of Ca2+ transients, respectively. A comparable dependence of spinous Ca2+ transients on relative timing was observed also when short bursts of APs and EPSPs were paired. These results indicate that the amplitude of the spinous Ca2+ transients during coincident pre- and postsynaptic activity depended critically on the relative order of subthreshold EPSPs and back-propagating APs. Thus, in neocortical neurons the amplitude of spinous Ca2+ transients could encode small time differences between pre- and postsynaptic activity.     

Nitric oxide and excitatory postsynaptic currents in immature rat sympathetic preganglionic neurons in vitro

PURPOSE: A disadvantage of ovoid shields in a Fletcher-type applicator is that these shields cause artifacts on postimplant CT images. CT images, however, make it possible to calculate the dose distribution in the rectum and the bladder. To be able to estimate the possible advantage of having CT information over the use of ovoid shields without having CT information, we investigated the influence of shielding segments in a Fletcher-type Selectron-LDR applicator on the dose distribution in rectum and bladder. METHODS AND MATERIALS: Contours of rectum and bladder were delineated on transaxial CT slices of 15 unshielded applications. Of the volumes contained within these structures dose-volume histograms (DVHs) were calculated. In a similar way, DVHs of simulated shielded applications were calculated. The reduction, due to shielding, of the dose to the 2 cm3 (D2) and 5 cm3 (D5) volume of the cumulative DVHs of rectum and bladder, were determined. An isodose pattern in the sagittal plane through the center of each applicator was plotted to compare the location of the shielded area with the location of maximum dose in rectum and bladder in the unshielded situation. In two cases local dose reductions to the rectal wall were determined by calculating the dose in points at 10-mm intervals on the rectal contours. RESULTS: For the rectum, the reduction of D2 ranged from 0 to 11.1%, with an average of 5.0%; the reduction of D5 ranged from 2.3 to 12.1%, with an average of 6.4%. The reduction of D2 and D5 for the bladder ranged from 0 to 11.9% and from 0 to 11.6%, with average values of 2.2 and 2.6%, respectively. In 8 out of 15 cases the rectal maximum dose was located inferior to the shielded area. In all cases except one the bladder maximum dose was located superior to the shielded area. Local dose reductions on the rectal wall can be as high as 30% or more in an optimally shielded area. CONCLUSIONS: Reductions of D2 and D5 to rectum and bladder due to shielding are rather small, because the shielded area does usually not coincide with the high dose region and even if it does, the shielded area is too small to result in large reductions of these values. Because local dose reductions vary largely, one should proceed with caution when calculating the dose in just one rectal or bladder reference point. Because large overall dose reductions cannot be achieved with shielding, it is safe to use an unshielded applicator when post implant CT images are used to realize optimized dose distributions.     

Integration of excitatory postsynaptic potentials in dendrites of motoneurons of rat spinal cord slice cultures

We examined the attenuation and integration of spontaneous excitatory postsynaptic potentials (sEPSPs) in the dendrites of presumed motoneurons (MNs) of organotypic rat spinal cord cultures. Simultaneous whole cell recordings in current-clamp mode were made from either the soma and a dendrite or from two dendrites. Direct comparison of the two voltage recordings revealed that the membrane potentials at the two recording sites followed each other very closely except for the fast-rising phases of the EPSPs. The dendritic recording represented a low-pass filtered version of the somatic recording and vice versa. A computer-assisted method was developed to fit the sEPSPs with a generalized alpha-function for measuring their amplitudes and rise times (10-90%). The mean EPSP peak attenuation between the two recording electrodes was determined by a maximum likelihood analysis that extracted populations of similar amplitude ratios from the fitted events at each electrode. For each pair of recordings, the amplitude attenuation ratio for EPSP traveling from dendrite to soma was larger than that traveling from soma to dendrite. The linear relation between mean ln attenuation and distance between recording electrodes was used to map 1/e attenuations into units of distance (micron). For EPSPs with typical time course traveling from the somatic to the dendritic recording electrode, the mean 1/e attenuation corresponded to 714 micron for EPSPs traveling in the opposite direction, the mean 1/e attenuation corresponded to 263 micron. As predicted from cable analysis, fast EPSPs attenuated more in both the somatofugal and somatopetal direction than did slow EPSPs. For EPSPs with rise times shorter than approximately 2.0 ms, the attenuation factor increased steeply. Compartmental computer modeling of the experiments with biocytin-filled and reconstructed MNs that used passive membrane properties revealed amplitude attenuation ratios of the EPSP traveling in both the somatofugal and somatopetal direction that were comparable to those observed in real experiments. The modeling of a barrage of sEPSPs further confirmed that the somato-dendritic compartments of a MN are virtually isopotential except for the fast-rising phase of EPSPs. Large, transient differences in membrane potential are locally confined to the site of EPSP generation. Comparing the modeling results with the experiments suggests that the observed attenuation ratios are adequately explained by passive membrane properties alone.     

Heterogeneity in the molecular composition of excitatory postsynaptic sites during development of hippocampal neurons in culture

To determine their roles in the assembly of glutamatergic postsynaptic sites, we studied the distributions of NMDA- and AMPA-type glutamate receptors; the NMDA receptor-interacting proteins alpha-actinin-2, PSD-95, and chapsyn; and the PSD-95-associated protein GKAP during the development of hippocampal neurons in culture. NMDA receptors first formed nonsynaptic proximal dendrite shaft clusters within 2-5 d. AMPA receptors were diffuse at this stage and began to cluster on spines at 9-10 d. NMDA receptor clusters remained partially nonsynaptic and mainly distinct from AMPA receptor clusters until after 3 weeks in culture, when the two began to colocalize at spiny synaptic sites. Thus, the localization of NMDA and AMPA receptors must be regulated by different mechanisms. alpha-Actinin-2 colocalized with the NMDA receptor only at spiny synaptic clusters, but not at shaft nonsynaptic or synaptic clusters, suggesting a modulatory role in the anchoring of NMDA receptor at spines. PSD-95, chapsyn, and GKAP were present at some, but not all, nonsynaptic NMDA receptor clusters during the first 2 weeks, indicating that none is essential for NMDA receptor cluster formation. When NMDA receptor clusters became synaptic, PSD-95 and GKAP were always present, consistent with an essential function in synaptic localization of NMDA receptors. Furthermore, PSD-95 and GKAP clustered opposite presynaptic terminals several days before either NMDA or AMPA receptors clustered at these presumptive postsynaptic sites. These results suggest that synapse development proceeds by formation of a postsynaptic scaffold containing PSD-95 and GKAP in concert with presynaptic vesicle clustering, followed by regulated attachment of glutamate receptor subtypes to this scaffold.     

Quantitative analysis of the gustatory evoked potentials in the guinea pig

Gustatory evoked potentials were studied in anesthetized guinea pigs to develop an objective and quantitative taste examination for patients with taste disorders. A positive wave was recorded by the application of NaCl, HCl or quinine hydrochloride solution. There was little difference in latency, duration and waveform among these three solutions. No apparent change in activity was seen after the application of sucrose solution or distilled water. The gustatory evoked potentials that excluded the influence of the trigeminal nerve innervating the tongue surface were able to be reproducibly recorded on either the cortical surface or the skull surface. There was a linear relationship between logarithmic values of potential amplitude and those of taste solution concentration. Therefore, it is suspected that the quantitative evaluation of taste detection is possible by measuring the taste solution concentration-potential amplitude relationship.     

Spontaneous excitatory postsynaptic currents in hippocampal CA1 pyramidal neurons of the gerbil after transient ischemia

The changes in the spontaneous excitatory postsynaptic currents (sEPSCs) after transient cerebral ischemia were studied using whole-cell recording from CA1 pyramidal neurons in the gerbil. In neurons recorded 1-2 days after ischemia, sEPSCs had a slowed time course with the decay time constant fitted by a single exponential and it progressively increased after ischemia. Frequency and amplitude distribution of sEPSCs in ischemic neurons were not significantly different from those in the control neurons. The results support the view that abnormal non-N-methyl-D-aspartic acid currents originate at the degenerated postsynaptic site, unrelated to the presynaptic releasing mechanisms.     

Helospectin/helodermin-like peptides in guinea pig lung: distribution and dilatory effects

The lower airways of guinea pigs were analysed for helospectin and helodermin using immunocytochemistry. A moderate supply of helospectin/helodermin-like immunoreactive nerve fibers and few nerve fibers displaying helodermin immunoreactivity was seen in the smooth muscle, around seromucous glands and small blood vessels in the trachea and around bronchi and pulmonary blood vessels. Helospectin I-, helospectin II- and helodermin-induced suppression of smooth muscle responses were analysed using isolated circular segments of trachea and pulmonary arteries of guinea pigs. In both airways and arteries the peptides caused a concentration-dependent relaxation of precontracted segments. The maximal relaxant activity observed was more pronounced in the airways than in the arteries. The effects of the helospectins and helodermin were compared to those of vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI), pituitary adenylate cyclase activating peptide (PACAP) and acetylcholine (ACh). All peptides, with the exception of PACAP, caused a total or nearly total relaxation of the precontracted tracheal segments. In the trachea PACAP was significantly more potent than the other five peptides whereas only small potency differences were seen in the pulmonary artery. The relaxant responses to helospectin I, helospectin II and helodermin in the trachea and the intrapulmonary arteries were unaffected by pretreatment with atropine, prazosin, yohimbine, propranolol, mepyramine and cimetidine. Conceivably, nerve fibers containing helospectin and helodermin may play a role in the regulation of airway resistance and in the regulation of local pulmonary blood flow.     

Characteristics of a fast transient outward current in guinea pig trigeminal motoneurons

A fast transient voltage dependent outward current (TOC) in trigeminal motoneurons (TMNs) was studied in guinea pig brainstem slices by use of sharp electrodes in combination with single electrode voltage clamp techniques. In solutions containing TTX, low Ca2+/Mn2+ and 20 mM TEA this current activated around -55 to -60 mV from holding potentials negative to resting potential, obtained its peak amplitude within 5 ms and decayed as a single exponential with a time constant of 6-8 ms. Half maximal values for inactivation and activation were -72 and -37 mV, respectively. Bath application of 5 mM 4-AP suppressed this current by approximately 90% and eliminated the early depolarizing transient membrane rectification observed in response to a constant depolarizing current pulse, prolonged the action potential duration, and reduced the threshold voltage and delay to onset of the action potential. It is suggested that this current resembles the typical A-current observed in many CNS neurons and, as a result of its voltage and time dependent properties, could contribute to control of motoneuronal discharge and timing of burst onset during rhythmical jaw movements. Therefore, any cellular models of masticatory activity should include the properties of this current.     

Large amplitude miniature excitatory postsynaptic currents in hippocampal CA3 pyramidal neurons are of mossy fiber origin

Neonatal (P0) gamma-irradiation was used to lesion selectively the mossy fiber (MF) synaptic input to CA3 pyramidal cells. This lesion caused a > 85% reduction in the MF input as determined by quantitative assessment of the number of dynorphin immunoreactive MF boutons. The gamma-irradiation lesion caused a reduction in the mean number of miniature excitatory postsynaptic currents (mEPSCs) recorded from CA3 pyramidal cells (2,292 vs. 1,429/3-min period; n = 10). The lesion also caused a reduction in the mean mEPSC peak amplitude from 19.1 +/- 0.45 to 14.6 +/- 0.49 pA (mean +/- SE; peak conductance 238.8 +/- 5.6 to 182.0 +/- 6.1 pS). Similarly, there was a reduction in the mean 10-85% rise time from 1.72 +/- 0.02 ms to 1.42 +/- 0.04 ms. The effects of the gamma-irradiation on both mEPSC amplitude and 10-85% rise time were significant at P < 0.002 and P < 0.005 (2-tailed Kolmogorov-Smirnov test). Based on the selectively of the gamma-irradiation, MF and non-MF mEPSC amplitude and 10-85% rise-time distributions were calculated. Both the amplitude and 10-85% rise-time distributions showed extensive overlap between the MF and non-MF mediated mEPSCs. The MF mEPSC distributions had a mean peak amplitude of 24.6 pA (307.5 pS) and a mean 10-85% rise time of 2.16 ms. THe non-MF mEPSC distributions had a mean peak amplitude of 12.2 pA (152.5 pS) and 10-85% rise time of 1.26 ms. The modes of the amplitude distributions were the same at 5 pA (62 pS). The MF and non-MF mEPSC amplitude and 10-85% rise-time distributions were significantly different at P < 0.001 (1-tailed, large sample Kolmogorov-Smirnov test). The data demonstrate that the removal of the MF synaptic input to CA3 pyramidal cells leads to the absence of the large amplitude mEPSCs that are present in control recordings.     

Optical studies of the biphasic modulatory effects of glycine on excitatory postsynaptic potentials in the chick brainstem and their embryogenesis

Multiple-site optical recording of transmembrane potential activity, using a voltage-sensitive dye, was employed to monitor neural activity from the nucleus tractus solitarius of the chick embryo. Optical signals related to glutamate-mediated excitatory postsynaptic potentials were evoked by a brief square current pulse applied with a microsuction electrode to the vagus nerve, and were recorded simultaneously from many sites in the brainstem slice preparation. We have found that glycine has biphasic modulatory effects on the glutamate-mediated excitatory postsynaptic potentials: at lower concentrations, glycine enhances the glutamate-mediated excitatory postsynaptic potential-related optical signal, and at higher concentrations, it reduces the glutamate-mediated excitatory postsynaptic potential-signal. The enhancing effect was insensitive to strychnine, but the reducing effect was blocked by strychnine, suggesting that the former effect was induced by glycine which increased glutamate binding to N-methyl-D-aspartate receptors, and the latter resulted from an increase in chloride conductance through the strychnine-sensitive inhibitory glycine receptors in postsynaptic neurons. The inhibitory effect of glycine was first observed in the brainstem preparations at the seven-day-old embryonic stage, and the enhancing effect was first observed in the nine-day-old preparations. We determined regional distributions of the biphasic effects of glycine in the seven- to nine-day old embryonic preparations. The spatial distribution of the enhancing effect appeared to be concentrated on the ventral side of the nucleus tractus solitarius, and the inhibitory effect was relatively concentrated in the medial portion. Furthermore, we compared the glycine effect with the effect of Mg(2)+ on N-methyl-D-aspartate receptors, and we have found that the Mg(2)+ site is functionally organized prior to the glycine site during embryonic development.     

Effects of K(+)-channel blockers on cochlear potentials in the guinea pig

The effects of different K+ channel blockers, 4-aminopyridine (4-AP), tetraethylammonium (TEA) and quinine, on the various cochlear potentials were observed by the means of perilymph infusion. Each of the three blockers depressed the compound action potential. However, they exerted quite different effects on other cochlear potentials, especially comparing 4-AP, a fast K(+)-channel blocker, with two other blockers. 4-AP induced a significant increase in the magnitude of summating potential, while TEA and quinine decreased it; 4-AP showed no effect on the general endocochlear potential (G-EP, the EP value recorded directly from the scala media, SM) and the negative EP component (N-EP), while TEA and Quinine increased G-EP and decreased the absolute value of N-EP. They also exerted different effects on the EP changes induced by exposure to intense noise. The results indicate the different roles of different K(+)-channels in the generation of cochlear potentials. The relationship of the two components of EP (positive and negative) and the G-EP was discussed.     

Effects of cortical stimulation on red nucleus neurons in the guinea pig

The aim of the present work was to study the control that the cerebral cortex exerts on red nucleus (RN) neurons in the guinea pig. The experiments were carried out in anaesthetized animals. Electrical stimulation of localized cortical foci was performed by tungsten microelectrodes in frontal and parietal regions containing sensorimotor representations of the body. Single unit RN activity was extracellularly recorded through glass micropipettes, and the encountered RN neurons were recognized by searching their peripheral receptive field. Then, corticorubral influences were tested on RN neurons whose receptive field was located in the same body regions where motor responses were evoked by cortical stimulation. The stimulation with a single pulse evoked complex responses, typically consisting of long lasting inhibitions sometimes preceded by a weak facilitation and always followed by an excitatory rebound. The application of a second pulse modified this pattern, depending on the time interval between the two stimuli. In fact, the reduction of the interval below 300 ms enhanced the excitatory components whereas it shortened the inhibitory component; moreover, an "early" facilitation was evoked but only at intervals as short as 50-150 ms, or less. These results suggest that the corticorubral control may vary according to different levels of cortical activation, becoming more and more facilitatory as the cortical discharges increase from low frequency values (tonic activity) towards high frequency values (phasic activity).     

The distribution of novel intermediate filament proteins defines subpopulations of myenteric neurons in rat intestine

BACKGROUND/AIMS: Recent studies with neurofilament antibodies as neuronal markers have shown subpopulations of myenteric neurons that do not contain neurofilament proteins. Novel neuronal intermediate filament proteins alpha-internexin, peripherin, and nestin have been identified. The aim of this study was to examine the distribution of these novel intermediate filaments in comparison with neurofilaments in myenteric plexus neurons. METHODS: Using indirect immunofluorescence techniques in whole-mount cryostat sections from neonate and adult rat small intestine and in primary cultures of myenteric neurons, the distribution of neurofilaments, alpha-internexin, peripherin, and nestin was studied in comparison with the neuronal marker protein gene product (PGP) 9.5 in myenteric neurons. RESULTS: Sixty-five percent of neurons contained neurofilament triplet proteins. alpha-Internexin and/or peripherin were found in the neurofilament-negative neurons. PGP 9.5 was present in 80% of the myenteric neurons. Of the neurons that were PGP negative, > 95% contained peripherin or alpha-internexin. Nestin was not found in either neonate or adult myenteric neurons but was seen in glial cells in culture. CONCLUSIONS: The results suggest that a subpopulation of myenteric neurons lacks neurofilament triplet proteins but contains either peripherin, alpha-internexin, or both. This selective distribution of intermediate filaments in subpopulations of enteric neurons may support differential roles in these structurally unique neurons.