Synaptic organization of the tectal-facial pathways in the cat. I. Synaptic potentials following collicular stimulation

1. The synaptic pathways underlying tectal influence over pinna movements were studied using an acute electrophysiological approach. Under pentobarbital anesthesia, postsynaptic potentials were recorded intracellularly in antidromically identified, cat facial motoneurons following electrical stimulation of the superior colliculus. How collicular topography is reflected in these synaptic potentials was examined using multiple stimulation sites. The pathways responsible for tectally evoked synaptic potentials were studied by making acute brain stem lesions and by intra-axonal horseradish peroxidase (HRP) staining. 2. Monosynaptic excitatory potentials (EPSPs) with latencies ranging from 0.7 to 1.1 ms and amplitudes that were always less than 1 mV were recorded in motoneurons following stimulation of the contralateral superior colliculus. Larger disynaptic EPSPs ranging in latency from 1.2 to 2.0 ms were recorded both in isolation and in association with monosynaptic EPSPs. In addition, disynaptic inhibitory synaptic potentials (IPSPs) with latencies ranging from 1.5 to 2.5 ms were observed, often in combination with monosynaptic EPSPs. Both disynaptic EPSPs and IPSPs were graded, augmented by multiple stimuli and found in all categories of motoneurons. 3. Stimulation of the ipsilateral superior colliculus produced nearly the same spectrum of potentials and latencies as did contralateral tectal stimulation. Occlusion between ipsi- and contralaterally evoked IPSPs suggests there might be a common element in the inhibitory disynaptic pathways. 4. More discrete populations of facial motoneurons were investigated. Specifically, motoneurons innervating the platysma and orbicularis oculi muscles, the intrinsic ear muscles, and muscles that move the vibrissae all displayed tectally elicited mono- and di-synaptic potentials. Collicular input was not restricted to motoneurons involved in orienting the pinnae. 5. The presence, polarity, and amplitude of the synaptic potentials evoked in individual facial motoneurons exhibited variations that were related to the site of stimulation in either the ipsi- or contralateral colliculus. These variations are compatible with the idea that the collicular input to facial motoneurons is topographically organized. 6. Acute lesions at the level of the superior olive indicated that the pathway producing the contralateral monosynaptic EPSPs runs, near the midline, ipsilateral to the target facial nucleus, whereas the contralateral disynaptic and the ipsilateral mono- and disynaptic pathways lie further lateral.(ABSTRACT TRUNCATED AT 400 WORDS)

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

Journal of Neurophysiology ◽

10.1152/jn.1990.64.2.381 ◽

1990 ◽

Vol 64 (2) ◽

pp. 381-402 ◽

Cited By ~ 16

Author(s):

P. J. May ◽

P. P. Vidal ◽

R. Baker

Keyword(s):

Retrograde Transport ◽

Synaptic Organization ◽

Facial Nucleus ◽

Afferent Pathways ◽

Postsynaptic Potentials ◽

Synaptic Potentials ◽

Midbrain Tegmentum ◽

Facial Musculature ◽

Long Latency ◽

Facial Motoneurons

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)

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The synaptic organization of optic afferents in the amphibian tectum

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1974.0086 ◽

1974 ◽

Vol 187 (1089) ◽

pp. 421-447 ◽

Cited By ~ 39

Keyword(s):

Optic Nerve ◽

Cell Layer ◽

Maximum Amplitude ◽

Synaptic Organization ◽

Nerve Fibres ◽

Synaptic Potentials ◽

Postsynaptic Cell ◽

Optic Fibre ◽

Stimulation Of

Potentials in the amphibian tectum, evoked by stimulation of the optic nerve, were recorded extracellularly. Four discrete potentials, referred to as the m 1 , m 2 , u 1 and u 2 waves, occur at different latencies after stimulation. We have shown that these waves represent summed post-synaptic potentials generated by synchronous activation of four different groups of optic nerve fibres. The m 1 and m 2 waves are generated by two classes of myelinated optic nerve fibres, previously characterized as ‘dimming’ and ‘event’ fibres. The maximum amplitude of the m 2 wave occurs just below, and of the m 2 wave just above, cell layer 8 of P. Ramón. The u 1 and u 2 waves are generated by ‘edge’ and ‘convexity’ fibres, respectively. The maximum amplitude of the u 1 wave occurs near the surface of the tectum, and of the u 2 wave some 100 μm below it. Postsynaptic cell bodies for all four classes of optic fibre are located in layer 8.

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Disynaptic Inhibition of Omnipause Neurons Following Electrical Stimulation of the Superior Colliculus in Alert Cats

Journal of Neurophysiology ◽

10.1152/jn.2001.85.6.2639 ◽

2001 ◽

Vol 85 (6) ◽

pp. 2639-2642 ◽

Cited By ~ 20

Author(s):

Kaoru Yoshida ◽

Yoshiki Iwamoto ◽

Sohei Chimoto ◽

Hiroshi Shimazu

Keyword(s):

Superior Colliculus ◽

Short Pulse ◽

Single Pulse ◽

Synaptic Organization ◽

Postsynaptic Potentials ◽

Disynaptic Inhibition ◽

Alert Cats ◽

Omnipause Neurons ◽

Pulse Stimulation ◽

Stimulation Of

We investigated the synaptic organization responsible for the inhibition of omnipause neurons (OPNs) following stimulation of the superior colliculus (SC) in alert cats. Stimulation electrodes were implanted bilaterally in the rostral and caudal SC where a short-pulse train induced small and large saccades, respectively. Effects of single-pulse stimulation on OPNs were examined with intracellular and extracellular recordings. In contrast to monosynaptic excitatory postsynaptic potentials, which were induced by rostral SC stimulation, inhibitory postsynaptic potentials were induced with disynaptic latencies (1.3–1.9 ms) from both the rostral and caudal SC in most OPNs. Analysis of a larger extracellular sample complemented intracellular observations. Monosynaptic activation of OPNs was elicited more frequently from rostral sites than from caudal sites, whereas spike suppression with disynaptic latencies was induced by caudal as well as rostral stimulation with similar frequencies. The results imply that disynaptic inhibition is produced by activation of SC cells that are distributed over wide regions related to saccades of different sizes. We suggest that signals from these neurons initiate a saccadic pause of OPNs through single inhibitory interneurons.

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Chapter II: Effects of brain stem lesions on actions evoked by natural stimulation of receptors

Acta Physiologica Scandinavica ◽

10.1111/j.1748-1716.1961.tb02372.x ◽

1961 ◽

Vol 54 ◽

pp. 22-22

Keyword(s):

Brain Stem ◽

Natural Stimulation ◽

Brain Stem Lesions ◽

Stem Lesions ◽

Stimulation Of

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Effects of low-frequency stimulation of the superior colliculus on spontaneous and visually guided saccades

Journal of Neurophysiology ◽

10.1152/jn.1993.69.3.953 ◽

1993 ◽

Vol 69 (3) ◽

pp. 953-964 ◽

Cited By ~ 43

Author(s):

P. W. Glimcher ◽

D. L. Sparks

Keyword(s):

Superior Colliculus ◽

Time Course ◽

Low Frequency ◽

Arbitrary Point ◽

Visually Guided ◽

Spontaneous Movements ◽

Low Frequency Stimulation ◽

Frequency Stimulation ◽

Stimulation Current ◽

Stimulation Of

1. The first experiment of this study determined the effects of low-frequency stimulation of the monkey superior colliculus on spontaneous saccades in the dark. Stimulation trains, subthreshold for eliciting short-latency fixed-vector saccades, were highly effective at biasing the metrics (direction and amplitude) of spontaneous movements. During low-frequency stimulation, the distribution of saccade metrics was biased toward the direction and amplitude of movements induced by suprathreshold stimulation of the same collicular location. 2. Low-frequency stimulation biased the distribution of saccade metrics but did not initiate movements. The distribution of intervals between stimulation onset and the onset of the next saccade did not differ significantly from the distribution of intervals between an arbitrary point in time and the onset of the next saccade under unstimulated conditions. 3. Results of our second experiment indicate that low-frequency stimulation also influenced the metrics of visually guided saccades. The magnitude of the stimulation-induced bias increased as stimulation current or frequency was increased. 4. The time course of these effects was analyzed by terminating stimulation immediately before, during, or after visually guided saccades. Stimulation trains terminated at the onset of a movement were as effective as stimulation trains that continued throughout the movement. No effects were observed if stimulation ended 40–60 ms before the movement began. 5. These results show that low-frequency collicular stimulation can influence the direction and amplitude of spontaneous or visually guided saccades without initiating a movement. These data are compatible with the hypothesis that the collicular activity responsible for specifying the horizontal and vertical amplitude of a saccade differs from the type of collicular activity that initiates a saccade.

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