Long-latency Excitatory Postsynaptic Potentials Research Articles

Electrical stimulation of the cholinergic laterodorsal tegmental nucleus elicits scopolamine-sensitive excitatory postsynaptic potentials in medial pontine reticular formation neurons

A large and consistent body of data implicates mesopontine cholinergic neurons in the production of rapid eye movement sleep, and indicates that many rapid eye movement sleep events are mediated by activation of pontine reticular formation neurons. There is anatomical evidence for projections from the mesopontine cholinergic nuclei to the pontine reticular formation, but no study has shown that stimulation of this cholinergic zone produces excitatory postsynaptic potentials in pontine reticular formation neurons. In the present study, intracellular recordings were made from 168 pontine reticular formation neurons, identified by antidromic activation from the bulbar reticular formation and by neurobiotin intracellular labeling, in acutely anesthetized cats. The effects of single-pulse electrical stimulation of the laterordorsal tegmental nucleus portion of the ipsilateral mesopontine cholinergic zone were evaluated in these neurons. Under urethane anesthesia this stimulation produced, in 21 of 22 recorded neurons, long-latency excitatory postsynaptic potentials (mean = 3 ms), consistent with the conduction velocity of unmyelinated cholinergic fibers (measured conduction velocity was 2 m/s). This excitatory postsynaptic potential was virtually abolished by intravenous administration of the muscarinic cholinergic receptor blocker scopolamine ( n = 40 neurons), and by acute cuts separating the laterodorsal tegmental nucleus and the recorded neurons ( n = 40). In contrast, a short-latency excitatory postsynaptic potential (0.7–1.5 ms) was not reduced in amplitude by scopolamine and could still be elicited following acute transverse cuts. Unlike the longer-latency excitatory postsynaptic potential, its amplitude was not reduced by barbiturate anesthesia. These data, suggesting the presence of an excitatory, cholinergic laterodorsal tegmental nucleus projection to the pontine reticular formation, provide further support to other lines of evidence implicating mesopontine cholinergic neurons in the production of rapid eye movement sleep, and are compatible with a model of rapid eye movement sleep generation in which a key element is mesopontine cholinergic input depolarizing and increasing the excitability of reticular core neurons.

Local synaptic circuits and epileptiform activity in slices of neocortex from children with intractable epilepsy.

1. Single and dual intracellular recordings were performed in neocortical slices obtained from tissue samples surgically removed from children (8 mo to 15 yr) for the treatment of intractable epilepsy. Electrical stimulation and glutamate microapplication were used to study local synaptic inputs to pyramidal cells. 2. In recordings with potassium-acetate electrodes, activation of presynaptic neocortical neurons with glutamate microdrops did not elicit a clear increase in postsynaptic potentials (PSPs) but did suppress current-evoked repetitive spike firing in recorded neurons. Bicuculline (10 microM) blocked this effect, suggesting it was caused by the activation of presynaptic gamma-aminobutyric acid (GABA) cells. In recordings with KCl electrodes, glutamate microdrops elicited an increase in the frequency and amplitude of depolarizing PSPs. Bicuculline (5-10 microM) blocked the glutamate-evoked PSPs, suggesting they were reversed GABAA-receptor-mediated inhibitory postsynaptic potentials (IPSPs). In one cell recorded with a KCl electrode (total n = 8), current-evoked spike trains elicited afterdischarges of reversed IPSPs, thus revealing a recurrent inhibitory circuit. Therefore local inhibitory synaptic circuits were robust and could be observed in tissue from patients as young as 11 mo. 3. In addition to short-latency (10-25 ms), monosynaptic excitatory postsynaptic potentials (EPSPs), electrical stimulation at low intensities sometimes elicited delayed EPSPs (20-60 ms). When GABAA-receptor-mediated synaptic inhibition was partially reduced in bicuculline (5-10 microM), electrical stimulation evoked large EPSPs at long and variable latencies (100-300 ms). Glutamate microapplication caused an increase in the frequency and amplitude of EPSPs; preliminary results suggest that glutamate microdrops were less likely to evoke EPSPs in tissue from younger patients (8-12 mo) than in slices from patients greater than 4 yr. Evidence for local excitatory synaptic circuits was thus found when synaptic inhibition was partially reduced. 4. After further reduction of inhibition in bicuculline (5-50 microM), electrical stimulation elicited epileptiform bursts. In pairs of simultaneously recorded neurons, bursts were generated synchronously from long-latency EPSPs (100-300 ms) in slices from patients as young as 8 mo. Reflected EPSPs at very long and variable latencies (500-1,100 ms) and repetitive epileptiform bursts could be evoked synchronously in pairs of cells. Glutamate activation of local presynaptic neurons elicited robust epileptiform events in recorded cells. This was seen in slices from patients as young as 16 mo. 5. These data provide physiological evidence for the presence of local inhibitory and excitatory synaptic circuits in human neocortex at least as early as 11 and 8 mo, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Organization of hindlimb muscle afferent projections to lumbosacral motoneurons in the chick embryo

We have examined the organization of muscle afferent projections to motoneurons in the lumbosacral spinal cord of chick embryos between stage 37, when muscle afferents first reach the motor nucleus, and stage 44, which is just before hatching. Connectivity between afferents and motoneurons was assessed by stimulating individual muscle nerves and recording the resulting motoneuron synaptic potentials intracellularly or electrotonically from other muscle nerves. Most of the recordings were made in the presence of DL-2-amino-5-phosphonovaleric acid (APV), picrotoxin, and strychnine to block long-latency excitatory and inhibitory pathways. Activation of muscle afferents evoked slow, positive potentials in muscle nerves but not in cutaneous nerves. These potentials were abolished in 0 mM Ca2+, 2mM Mn2+ solutions, indicating that they were generated by the action of chemical synapses. The muscle nerve recordings revealed a wide-spread pattern of excitatory connections between afferents and motoneurons innervating six different thigh muscles, which were not organized according to synergist-antagonist relationships. This pattern of connectivity was confirmed using intracellular recording from identified motoneurons, which allowed the latency of the responses to be determined. Short-latency potentials in motoneurons were produced by activation of homonymous afferents and the heteronymous afferents innervating the hip flexors sartorius and anterior iliotibialis. Stimulation of anterior iliotibialis afferents also resulted in some short-latency excitatory postsynaptic potentials (EPSPs) in motoneurons innervating the knee extensor femorotibialis, though other connections were of longer latency. Afferents from the adductor, a hip extensor, did not evoke short-latency EPSPs in any of these three types of motoneurons. Short-latency, but not long-latency EPSPs, persisted during repetitive stimulation at 5 Hz, suggesting that they were mediated monosynaptically. Long-latency, fatigue-sensitive potentials were maintained in the presence of APV, picrotoxin, and strychnine, suggesting that polysynaptic pathways utilize non-NMDA receptors as well as NMDA receptors. We found no difference in the pattern of inputs to femorotibialis motoneurons between stage 37-39 and near hatching at stage 44, suggesting muscle afferent projections to these motoneurons are correct at stage 37, when the afferents first reach the lateral motor column in substantial numbers.

Synaptic responses of guinea pig and rat central amygdala neurons in vitro

1. To investigate postsynaptic potentials (PSPs), we made intracellular recordings from neurons of the amygdaloid central nucleus in slices from the guinea pig and rat brains maintained in vitro. The results from guinea pigs and rats were very similar. 2. In the presence of bicuculline (20 microM), focal electrical stimulation of the amygdaloid basal nucleus with low intensities elicited short-latency excitatory PSPs (EPSPs) followed by long-latency EPSPs. The short-latency EPSP was selectively blocked by 6-cyano-7-nitroquinoxaline-2,3-dion (CNQX; 10-20 microM). The long-latency EPSP was preferentially abolished by D,L-2-amino-5-phosphonovaleric acid (D,L-APV; 40 microM) and was augmented by removal of extracellular Mg2+. The compound EPSP reversed at -4 mV, which was close to -1 mV, the reversal potential for pressure-ejected glutamate (Glu). 3. When the intensity of the focal stimulation was increased in the presence of bicuculline (20 microM), CNQX (20 microM), and D,L-APV (50 microM), a second EPSP with a short latency and a prolonged duration could be evoked in approximately 65% of the neurons. The EPSPs were reversibly blocked by d-tubocurarine (50 microM) or hexamethonium (200 microM) but were unaffected by atropine (1 microM) or a 5-hydroxytryptamine type 3 receptor antagonist, ICS-205930 (5-10 microM). In these neurons, acetylcholine (ACh; 1-3 mM) caused a depolarization, associated with a decreased input resistance. 4. In the presence of CNQX (20 microM) and D,L-APV (50 microM), single focal stimulation of the dorsolateral subdivision in the central nucleus with low intensities elicited a depolarizing inhibitory PSP (IPSP). The IPSP was reversibly abolished by bicuculline (20-40 microM). The reversal potential (-63 mV) for the IPSP was similar to the reversal potential (-61 mV) for the response to gamma-aminobutyric acid (GABA) applied by pressure ejection. 5. In the presence of bicuculline (20-40 microM) and CNQX (20 microM), a repetitive focal stimulus with high intensities delivered to the dorsolateral subdivision produced a hyperpolarizing PSP followed by a slow depolarization in most neurons. Of putative inhibitory amino acid transmitters, glycine (Gly; 3 mM) produced only a hyperpolarization, associated with a decrease in input resistance. Strychnine (1-2 microM) reversibly blocked both the Gly hyperpolarization and the synaptically evoked hyperpolarization. The reversal potential of -81 mV for the hyperpolarizing PSP was close to -82 mV for the Gly hyperpolarization. The reversal potential for the Gly response was shifted to less negative values by increasing the external K+ concentration or decreasing the extracellular Cl- concentration.(ABSTRACT TRUNCATED AT 400 WORDS)

Synaptic organization of tectal-facial pathways in cat. II. Synaptic potentials following midbrain tegmentum stimulation

1. The organization of the synaptic pathways underlying midbrain tegmentum influence over the facial musculature was studied with the use of an acute electrophysiological approach in the cat. Under pentobarbital sodium anesthesia, synaptic potentials were recorded intracellularly in antidromically identified facial motoneurons following electrical stimulation of the paralemniscal zone. The cells of origin and the pathways responsible for the potentials evoked from the paralemniscal zone were defined with the use of retrograde transport of horseradish peroxidase (HRP). The putative role of the paralemniscal zone with regard to the production of disynaptic, tectally evoked potentials in facial motoneurons was investigated both by inactivating this nucleus with injections of lidocaine and by making acute brain stem lesions to sever the paralemniscal-facial and other afferent pathways. 2. Following paralemniscal stimulation, monosynaptic, excitatory postsynaptic potentials (EPSPs) with latencies ranging from 0.6 to 0.9 ms, steep rising phases, and amplitudes in excess of 4.0 mV were recorded in motoneurons of the temporal and auriculoposterior subdivisions, which supply the pinna muscles. Smaller amplitude EPSPs (less than 1.0 mV) with monosynaptic latencies were observed in the zygomatic subdivision. Polysynaptic EPSPs with latencies ranging from 1.0 to 1.8 ms were also observed in all three of these subdivisions. However, only long-latency EPSPs, arriving at 2.0 ms or later, were present in ventral subdivision motoneurons. 3. Inhibitory postsynaptic potentials (IPSPs) were also frequently recorded in facial motoneurons after paralemniscal stimulation. Monosynaptic IPSPs with latencies ranging from 0.8 to 1.2 ms and amplitudes in excess of 4.0 mV were recorded in facial motoneurons of the temporozygomatic and auriculoposterior subdivisions, as were polysynaptic IPSPs with latencies ranging from 1.2 to 1.8 ms. IPSPs were sometimes observed in combination with a smaller, shorter latency EPSPs. Only long-latency IPSPs of greater than 2.0 ms were recorded in ventral subdivision motoneurons. In all cases, both the EPSPs and the IPSPs were graded in character and could be augmented by multiple stimuli. 4. The contralateral paralemniscal zone and the supraoculomotor area, bilaterally, represented the two most prominent afferent sources labeled after HRP injection of the facial nucleus. The superior colliculus and numerous reticular formation regions were also identified as facial nucleus afferents by the presence of retrogradely labeled cells. The retrogradely labeled cells in the paralemniscal zone exhibited heterogeneous soma size. HRP-labeled axons of the paralemniscal-facial pathway were observed to cross the midline by traveling ventral to the brachium conjunctivum in the caudal mesencephalon.(ABSTRACT TRUNCATED AT 400 WORDS)