Postsynaptic potentials of tectal neurons evoked by electrical stimulation of the pretectal nuclei in bullfrogs (Rana catesbeiana)

Postsynaptic responses of the tectal cells to electrical stimulation of pretectal (Lpd/P) nuclei were intracellularly recorded in the bullfrog (Rana catesbeiana). The pretectal stimulation elicited mainly two types of responses in the ipsilateral tectum: an EPSP followed by an IPSP and a pure IPSP. The latter predominates in the tectal cells responding to ipsilateral pretectal stimulation. In a few cells, biphasic hyperpolarization appeared under stronger stimulus intensities. Only one type of response was found in the contralateral tectum, a pure IPSP. The antidromically invaded tecto-pretectal projecting cells were recorded in both tecta, which revealed reciprocal connections between the tectum and particular pretectal nuclei. This paper demonstrates the synaptic nature underlying pretectotectal information transfer. EPSPs with short latencies were concluded to be monosynaptic. Most IPSPs were generated through polysynaptic paths, but monosynaptic IPSPs were also recorded in both optic tecta. Nearly 98% of impaled tectal cells (except for intra-axonally recorded and antidromically invaded cells) showed inhibitory responses to pretectal stimulation. The results provide strong evidence that pretectal cells broadly inhibit tectal neurons as suggested by behavioral and extracellular recording studies.     

Ascending and descending convergent inputs to neurons in the nucleus parabrachialis of the rat: an intracellular study

Responses of the nucleus parabrachialis neurons (PBN) to electrical stimulation of the lateral hypothalamus (HL), central nucleus of the amygdala (Ac), dorsolateral funicullus in the spinal cord (SC), mediocaudal nucleus tractus solitarius (NTS), and substantia nigra (SN) were investigated in anesthetized rats by intracellular recording technique. Convergent excitatory postsynaptic potentials (EPSPs) were evoked on 8 of 36 neurons tested by both HL and NTS stimulation. The EPSPs evoked by HL stimulation were characterized as monosynaptic in 4 neurons. The EPSPs evoked by SC stimulation were characterized as monosynaptic in 2 of 36 neurons, moreover, these neurons were also antidromically activated by HL stimulation. Stimulation of Ac evoked EPSPs on 10 of 36 cells tested; 8 demonstrated to be monosynaptic. In addition, IPSP evoked by SN stimulation and EPSP evoked by NTS stimulation converged on three neurons. The results indicate that ascending and descending inputs converge on lateral PBN neurons.     

Morphology and laminar distribution of electrophysiologically identified cells in the pigeon's optic tectum: an intracellular study

The responses of 65 cells to electrical stimulation of the contralateral optic nerve were intracellularly recorded in the pigeon optic tectum by using micropipettes filled with a solution of horseradish peroxidase. Nineteen of them were successfully labeled. Microscopic examination of the filled cells shows that our sample includes six pyramidal, ten ganglion, two stellate, and one bipolar horizontal cells. Thus, pyramidal and ganglion neurons constitute the most numerous types of cells in our sample. Pyramidal cells were located in layer II but mostly in its non-retinorecipient part, and they had restricted ascending dendritic trees oriented orthogonal to the tectal lamination. Ganglion cells were located in layer III with one exception, which was in sublayer IIi. These cells had non-oriented dendritic trees which ramify over considerable distances. Terminal dendritic branches from a number of pyramidal and ganglion cells extended superficially well within the region of optic fibers termination. In our study, ganglion cells constituted the efferent tectal elements. Pyramidal cells responded to optic nerve stimulation with a pure EPSP, with an EPSP-IPSP sequence, or with a pure IPSP. Ganglion cells always exhibited an IPSP either alone or preceded by an EPSP. Stellate and bipolar cells responded with a pure EPSP. The study of the laminar distribution of labeled and non-labeled cells shows from surface to depth, a gradual increase in the number of cells responding with an EPSP-IPSP or with a pure IPSP and a gradual decrease in the number of those exhibiting a pure EPSP. The analysis of the sensitivity of EPSPs and IPSPs to high frequency optic nerve stimulation shows that monosynaptic as well as polysynaptic EPSPs can be recorded from cells in the non-retinorecipient tectal region, a number of ganglion and pyramidal cells receive a direct retinal excitatory input as their dendrites pass through the region of optic endings, most IPSPs are polysynaptic, some cells located in the retinorecipient region may receive direct retinal inhibitory connections.     

青蛙前视盖与视顶盖间神经传导的细胞内电生理研究(英文)

目的已有许多研究报告了青蛙的前视盖对视顶盖起抑制作用,但关于此神经活动的特性尚不清楚。本研究探讨了这种复杂的神经活动的机理。方法用细胞内记录方法,通过电刺激前视盖的神经细胞核来记录视顶盖细胞的神经活动。结果前视盖的电刺激在同侧视顶盖主要唤起了两种神经反应:一种是兴奋性(excitatory postsynaptic potential,EPSP)和抑制性突触后电位(an inhibitory postsynaptic potential,IPSP)同时出现,另一种是单纯的IPSP,后者在本记录中占主导地位。另外我们也记录到了某些投射到前视盖的视盖投射细胞的神经电位。它揭示了视顶盖和前视盖之间存在着交叉性的相互作用。短潜时的EPSP可能是通过单突触进行传导的,而大多数的IPSP是通过多突触方式进行神经信息传递的。几乎98%被记录的视盖细胞对前视盖的刺激显示出了抑制性反应。结论前视盖的神经细胞对视顶盖的神经活动发挥了强烈的抑制性作用。     

青蛙前视盖与视顶盖间神经传导的细胞内电生理研究

目的已有许多研究报告了青蛙的前视盖对视顶盖起抑制作用,但关于此神经活动的特性尚不清楚。本研究探讨了这种复杂的神经活动的机理。方法用细胞内记录方法,通过电刺激前视盖的神经细胞核来记录视顶盖细胞的神经活动。结果前视盖的电刺激在同侧视顶盖主要唤起了两种神经反应：一种是兴奋性（excitator ypostsynaptic potential,EPSP）和抑制性突触后电位（an inhibitory postsynaptic potential,IPSP）同时出现,另一种是单纯的IPSP,后者在本记录中占主导地位。另外我们也记录到了某些投射到前视盖的视盖投射细胞的神经电位。它揭示了视顶盖和前视盖之间存在着交叉性的相互作用。短潜时的EPSP可能是通过单突触进行传导的,而大多数的IPSP是通过多突触方式进行神经信息传递的。几乎98％被记录的视盖细胞对前视盖的刺激显示出了抑制性反应。结论前视盖的神经细胞对视顶盖的神经活动发挥了强烈的抑制性作用。     

Group III mGluR-mediated depression of sensory synaptic transmission

The effect of L-AP4, a group III mGluR agonist, on sensory synaptic transmission in the lamprey spinal cord has been analyzed. Paired recordings were made between cutaneous mechanosensory neurons (dorsal cells) and postsynaptic spinobulbar giant interneurons. L-AP4 reduced the monosynaptic dorsal cell-evoked EPSP, but at concentrations higher (200-500 microM) than those necessary to depress reticulospinal axon-evoked EPSPs. Stimulation of the dorsal column, which contains dorsal cell axons and the axons of putative nociceptive and theromosensory axons, elicited compound EPSPs that were consistently depressed by L-AP4. Sensory inputs in the lamprey are thus inhibited by group III mGluRs.     

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)     

Synaptic transmission of excitation from the retina to cells in the pigeon's optic tectum

Intracellular recordings were used to study the synaptic excitation of optic tectum neurons in the pigeon. Electrical stimulation of both contralateral optic nerve and ipsilateral optic tract evoked in the tectal neurons EPSPs which in most cases were followed by an IPSP. An extrapolation procedure based on response latency was used to reveal that the EPSPs were mediated by way of mono-, di- and polysynaptic connections with the retinal endings. The laminar location of the recorded cells was estimated according to the field potential and the recording depth with the exception of the cell which was intracellulary stained with HRP. Monosynaptic EPSPs were recorded from cells in the retinorecipient region (sublayers IIa-f) as well as in the non-retinorecipient region (sublayers IIg-j and layer III) of the tectum, while di- and polysynaptic EPSPs were never recorded from the input layers. Tectofugal projections arise largely from layer III neurons. Thus, these results indicate that retinal excitation is transmitted to the output tectal cells by way of mono-, di- or polysynaptic pathways. The conduction velocities of most retinal fibers mediating the EPSP ranged from 4 to 22 m/s (average 12 m/s). However, in a number of retinal fibers the conduction velocities were in a faster range, up to 36 m/s.     

Synaptic activation of the interneurons of the thoracic portion of the spinal cord by reticulospinal fibers of the lateral funiculus

Synaptic processes evoked in various functional groups of thoracic interneurons (Th10,11) by stimulation of ipsi- and contralateral bulbar reticular formation were studied in anesthetized cats with lesions of the spinal cord that remained intact only the ipsilateral funiculus. Activation of reticulospinal fibres of the lateral funiculus with conduction velocities of 30-100 m/s evoked monosynaptic EPSPs in the following types of cells tested: monosynaptically excited by group la muscle afferents; excited by flexor reflex afferents; excited mainly by descending systems; excited by low-threshold cutaneous afferents to a less extent. All these neurons with responses to reticular stimulation were located predominantly in the central and lateral regions of Rexed's lamina VII. Most of the cells in the dorsal horn were not affected by short-latency reticulofugal influences. The only exception were 6 neurons located in the horn most dorsal laminae. Functional organization of connections between the lateral reticulospinal pathways and spinal neurons is discussed as compared to that of medial reticulo-spinal pathways as well as to the organization of "lateral" descending systems: cortico- and rubro-spinal.     

Catecholamine varicosities in cat dorsal root ganglion and spinal ventral roots

Convergence upon reticulospinal neurons which mediate disynaptic, contralateral pyramidal EPSPs to neck motoneurons has been examined in cats with contralateral pyramidal transection at the obex. Conditioning stimuli in the contralateral tectum and ipsilateral mesencephalic tegmentum produced monosynaptic facilitation of the disynaptic pyramidal EPSP, whereas facilitation evoked from the ipsilateral pyramid showed a disynaptic time course. These results show that contralateral pyramidal, tectal and ipsilateral tegmental fibers converge onto common reticulospinal neurons which have direct excitatory connections with neck motoneurons.     

Excitatory and inhibitory transmission from dorsal root afferents to neonate rat motoneurons in vitro

Intracellular recordings were made from antidromically identified motoneurons in neonate (12-22 days) rat transverse spinal cord slices and the transmitters and receptors probably involved in initiating the excitatory (EPSP) and inhibitory (IPSP) postsynaptic potentials were investigated. Stimulation of dorsal roots elicited in motoneurons an EPSP, an IPSP, or an EPSP followed by an IPSP. EPSPs in 70% of motoneurons had a short latency (less than or equal to 1 ms) and in the remaining cells a latency longer than 1 ms. The IPSPs had a long latency (greater than or equal to 1 ms). Short- and long-latency EPSPs were enhanced by the acidic amino acid uptake inhibitor L-aspartic acid-beta-hydroxamate (AAH) and depressed by the non-selective glutamate receptor antagonists gamma-D-glutamylglycine (DGG) and kynurenic acid. Short-latency EPSPs were suppressed by the quisqualate/kainate (QA/KA) receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) but not by the N-methyl-D-aspartate (NMDA) receptor antagonists D-(-)-2-amino-5-phosphonovaleric acid (APV) and ketamine. Long-latency EPSPs were reduced by DNQX as well as by APV and ketamine. Superfusion of the slices with a Mg-free solution increased the EPSPs and unmasked a late, APV-sensitive component. The IPSP was reduced by the glycine antagonist strychnine as well as by APV and ketamine but resistant to DNQX. The results indicate that stimulation of dorsal roots elicited in motoneurons a monosynaptic EPSP mediated by glutamate/aspartate acting predominantly on the QA/KA subtype of glutamate receptors; an NMDA component can be unveiled in Mg-free solution.(ABSTRACT TRUNCATED AT 250 WORDS)     

The relationship between the second zone of the auditory cortex and the medial geniculate body and first auditory zone]

Extracellular and intracellular responses of the second auditory (AII) cortical neurons to stimulation of geniculocortical fibres and first auditory cortex (AI) were studied in experiments carried out on cats immobilized with d-tubocurarine. It is shown that in these neurons there appear antidromic, mono-, di- and polysynaptic spike potentials to geniculate and AI stimulation. The number of antidromic reactions was about twice as low as in AI under the same conditions. Di- and polysynaptic responses predominated among orthodromic reactions. Intracellular recording revealed EPSP, EPSP-IPSP and primary IPSP in AII neurons. Response latencies in AII neurons to AI stimulation were in the range of 0.75-6.0, 6.1-16.0, 18.0-23.0 and 60.100 ms. After the medial geniculate body was removed, the number of responses with a latency of 6.1-16.0 ms decreased considerably. In some neurons spike pontentials appeared both to geniculate and AI stimulation. Comparison of the response latencies at both types of stimulation showed that impulses from AI come in AII not only to the neurons that are inputs for MGB impulses but also to neurons in the sebsequent link of intracortical neuronal chain. In most AII neurons disynaptic IPSP appeared at AI stimulation. Only in one case IPSP with a latency of 1.0 ms was recorded being probably monosynaptic.     

Slow EPSP and the depolarizing action of noradrenaline on sympathetic preganglionic neurons

Intracellular recordings were made from sympathetic preganglionic neurons of the lateral horn in slices of cat thoracic cord maintained in vitro. Focal electrical stimulation of the slice evoked, in addition to the already described fast EPSPs, EPSPs of several seconds duration. The slow EPSPs, like the fast EPSPs, were graded with stimulus intensity and were abolished by TTX or low Ca and high Mg superfusion. The slow EPSP decreased in amplitude with membrane hyperpolarization and was nullified at -90 mV but did not reverse with further hyperpolarization. The slow EPSP was abolished by phentolamine or prazosin but not by yohimbine. Noradrenaline NA, 10-50 microM) caused in 30% of neurons a TTX-resistant depolarization. The NA-evoked depolarization had the same characteristics as the slow EPSP with respect to sensitivity to membrane potential and to adrenergic blockers. These results suggest that NA, acting on an alpha 1-receptor, may be the mediator of the slow EPSP evoked in this neuron by focal stimulation.     

Hippocampal inputs to identified neurons in an in vitro slice preparation of the rat nucleus accumbens: evidence for feed-forward inhibition.

The aim of the present study was to analyze responses of nucleus accumbens neurons to stimulation of the fornix. The recorded neurons were labeled with biocytin and identified as medium spiny neurons. A large majority of cells generated a depolarizing postsynaptic potential in response to stimulation of the fornix. Using intracellular current injection, this depolarizing response was dissociated into an EPSP reversing at -6 +/- 6 mV and an IPSP reversing at -71 +/- 4 mV. Both the EPSP and IPSP were abolished by 6-cyano-7-nitroquinoxaline-2,3-dione. In addition, the IPSP was blocked by bicuculline and picrotoxin. The onset latency of the EPSP was constant in spite of varying stimulus intensities. In contrast, the onset latency of the IPSP increased with decreasing stimulus intensity. Notably, the stimulus threshold for evoking IPSPs was generally lower than for EPSPs. At stimulus intensities well above threshold, the IPSP onset was only slightly delayed with respect to the EPSP onset. These results indicate that the EPSP can be characterized as a monosynaptic and glutamate-mediated synaptic response. The IPSP, however, appears to be mediated by a disynaptic feed-forward pathway involving both glutamate and GABAA receptors. Recurrent and lateral inhibitory interactions have previously been proposed to be predominant organizational principles in the caudate-putamen and nucleus accumbens. This study indicates that feed-forward inhibition is an additional principle governing the activities of striatal neural networks.     

Lemniscal Input to Identified Neurons of the Central Nucleus of Mouse Inferior Colliculus: an Intracellular Brain Slice Study

Intracellular recordings were performed in 34 neurons in the central nucleus of the inferior colliculus in brain slice preparations of the mouse. Sixteen neurons recorded were stained intracellularly by injection of biocytin and identified as multipolar. After electrical stimulation of the lateral lemniscus, 32 of 34 neurons exhibited postsynaptic potentials (PSPs). Onset latencies of the PSPs were 5.0±2.8 ms (range 2-12 ms), presumably reflecting the lack of a significant monosynaptic input to most of the neurons recorded. An excitatory PSP (EPSP), often followed by a late inhibitory PSP (IPSP), was present in all neurons which received synaptic input. The IPSPs usually had a reversal potential positive to the cell's resting membrane potential, thus working as shunting inhibitors. Superfusion of the slice with the GABA_A antagonist bicuculline resulted in blockade of the IPSP and pronounced prolongation of the EPSP. In 50% of these cases, paroxysmal depolarizing shifts were observed in the presence of bicuculline. Blocking the non-NMDA glutamate receptors with 6,7-dinitroquinoxaline-2,3-dione resulted not only in the total disappearance of EPSPs but also of late IPSPs, indicating that the latter depend on the glutamatergic EPSPs. Furthermore, all neurons recorded must receive substantial innervation from sources within the inferior colliculus, together constituting a complex neuronal network in the inferior colliculus with an important role of the inhibitory neurotransmitter GABA in controlling network properties.     

Inhibition of protein kinase activity enhances long-term potentiation of hippocampal IPSPs.

In this study on guinea pig hippocampal slices, protein kinase C (PKC) involvement in long-term potentiation (LTP) of GABAA and GABAB receptor-mediated fast and slow IPSPs, respectively, was examined. Stimulation of the stratum radiatum induced EPSPs followed by fast and slow IPSPs in the CA1 neurons. Tetanic stimulation of the stratum caused a marginal LTP of the fast IPSP but not of the slow IPSP. When K-252b, a potent inhibitor of PKC, was injected into CA1 neurons, LTP of fast and slow IPSPs was observed. These results indicate that PKC activation in CA1 neurons is involved in minimizing, rather than inducing, LTP of the IPSPs so that the EPSP is not distorted.     

Endogenous and exogenous dopamine presynaptically inhibits glutamatergic reticulospinal transmission via an action of D2-receptors on N-type Ca2+ channels

In this study, the effects of exogenously applied and endogenously released dopamine (DA), a powerful modulator of the lamprey locomotor network, are examined on excitatory glutamatergic synaptic transmission between reticulospinal axons and spinal neurons. Bath application of DA (1-50 micro m) reduced the amplitude of monosynaptic reticulospinal-evoked glutamatergic excitatory postsynaptic potentials (EPSPs). The effect of DA was blocked by the D2-receptor antagonist eticlopride, and mimicked by the selective D2-receptor agonist 2,10,11 trihydroxy-N-propyl-noraporphine hydrobromide (TNPA). Bath application of the DA reuptake blocker bupropion, which increases the extracellular level of dopamine, also reduced the monosynaptic EPSP amplitude. This effect was also blocked by the D2-receptor antagonist eticlopride. To investigate if the action of DA was exerted at the presynaptic level, the reticulospinal axon action potentials were prolonged by administering K+ channel antagonists while blocking l-type Ca2+ channels. A remaining Ca2+ component, mainly dependent on N and P/Q channels, was depressed by DA. When DA (25-50 micro m) was applied in the presence of omega-conotoxin GVIA, a toxin specific for N-type Ca2+ channels, it failed to affect the monosynaptic EPSP amplitude. DA did not affect the response to extracellularly ejected d-glutamate, the postsynaptic membrane potential, or the electrical component of the EPSPs. DA thus acts at the presynaptic level to modulate reticulospinal transmission.     

A physiological study of the monosynaptic reflex responses of cat spinal alpha-motoneurons after partial lumbosacral deafferentation

In adult cats the whole S1 and rostral half of the L7 dorsal roots were cut on the left side of the spinal cord to produce a partial monosynaptic deafferentation of the ipsilateral alpha-motoneurons. Three, 6 or 12 weeks later, monosynaptic reflexes (MSRs) were recorded from the L6, L7 and S1 ventral roots or from various peripheral nerves during stimulation of the L6 and remaining parts of the L7 dorsal roots. Also, monosynaptic excitatory postsynaptic potentials (EPSPs) were recorded intracellularly in different types of medial gastrocnemius alpha-motoneurons of the L7 segment during stimulation of various hind limb muscle nerves. The right side with an identical acute deafferentation served as control. On the chronically lesioned side the MSRs were increased in size, also during post-tetanic potentiation. The monosynaptic EPSPs had increased amplitudes in all motoneuron types, but the relation in EPSP size between different motoneuron types as well as between different synergistic inputs remained largely unchanged. EPSP rise times were not changed, and aberrant monosynaptic connections from non-synergist muscles were not observed. It is concluded that the extent of reactive reflex changes may be related to both the number of vacant synaptic sites and the degree of functional synergism between the eliminated and remaining monosynaptic pathways. Possible underlying mechanisms are discussed.     

Lack of binocular inhibition in monocular segment of lateral geniculate nucleus of rabbits

Intracellular recordings from slow relay cells in the rabbit lateral geniculate nucleus demonstrated that the slow cells, just like the fast ones, receive a monosynaptic EPSP and a trisynaptic IPSP from the optic nerve. The IPSP is most likely mediated by interleurones activated by recurrent collaterals of the relay cell axon. In slow relay cells, both the EPSP and the IPSP from the optic nerve are brought about via the same group of slowly-conducting fibers. No mutual inhibition between the fast and the slow conducting system was observed in the rabbit lateral geniculate nucleus.     

Serotonin mimics tail shock in producing transient inhibition in the siphon withdrawal reflex of Aplysia

Tail shock-induced modulation of the siphon withdrawal reflex of Aplysia has recently been shown to have a transient inhibitory component, as well as a facilitatory component. This transient behavioral inhibition is also seen in a reduced preparation in which a cellular reflection of the inhibitory process, tail shock-induced inhibition of complex EPSPs in siphon motor neurons, is observed. The biogenic amine serotonin (5-HT) is known to play a role in the facilitatory aspects of sensitization in Aplysia. The aim of this article was to examine whether 5-HT might also contribute to the inhibitory effects of tail shock in the siphon withdrawal reflex. To examine this question, we carried out two kinds of experiments. First, in the isolated abdominal ganglion, we recorded intracellularly from siphon motor neurons and examined the effects of 5-HT on (1) complex (polysynaptic) EPSPs, produced by siphon nerve stimulation, and, simultaneously, (2) monosynaptic EPSPs from siphon sensory neurons. We found that, paralleling the effects of tail shock in the reduced preparation, 5-HT produced transient inhibition of the complex EPSP; the monosynaptic EPSP was facilitated by 5-HT. Second, we examined the behavioral effects of 5-HT on siphon withdrawal in a reduced preparation. We found that 5-HT again paralleled tail shock by producing transient inhibition of the siphon withdrawal reflex. Our results suggest that, in addition to its well-established facilitatory role in reflex modulation in Aplysia, 5-HT might play an important inhibitory role, as well.