An analysis was made of effects of 0.1-1.0 mg/kg 4-aminopyridine (4-AP) i.v. on excitatory and in... more An analysis was made of effects of 0.1-1.0 mg/kg 4-aminopyridine (4-AP) i.v. on excitatory and inhibitory spinal reflex pathways in lightly anaesthetized or decerebrated cats. The effects appeared within the first minutes of the injection, reached maximum after about 10-15 min and remained stable during at least several hours. 4-AP enhanced the following synaptic actions on motoneurones: monosynaptic excitation from Ia afferents and descending tracts, disynaptic and polysynaptic excitation from group Ib, group II, cutaneous and high threshold muscle afferents, disynaptic inhibition from Ia and Ib afferents and recurrent and polysynaptic inhibition from different afferents. 4-AP also increased primary afferent depolarization and excitation of ascending tract cells by peripheral stimuli. In the case of the disynaptic inhibitory pathways it has been shown that 4-AP may enhance the excitation of the interposed interneurones but it also increases the action of these interneurones on the motoneurones; monosynaptic inhibition evoked in motoneurones by electrical stimulation of the axons of the inhibitory interneurones was used as a test response in these experiments. No indications were found of direct effects of 4-AP on excitability of afferent fibres or motoneurones to electrical stimuli. No systematic changes were either found in the membrane potential of motoneurones or in the duration of action potentials of these neurones or primary afferents. It is therefore concluded that small doses of 4-AP enhance synaptic transmission in the spinal cord by an action at a presynaptic level.
ABSTRACT We describe here an automatic selection method to retrieve spontaneous cord dorsum poten... more ABSTRACT We describe here an automatic selection method to retrieve spontaneous cord dorsum potentials from the spinal cord in the anesthetized cat. Previous studies have indicated that some of these potentials appear synchronized in several spinal segments and are generated by the activation of specific sets of dorsal horn neurons. Since their synchronization is affected in a characteristic manner by acute peripheral nerve and spinal lesions, as well as during capsaicin-induced skin inflammation, they can be used to describe the patterns of functional interconnectivity between specific sets of dorsal horn neurons, which makes them of potential clinical interest.
In the spinal cord of the anesthetized cat, we measured the changes in extracellular concentratio... more In the spinal cord of the anesthetized cat, we measured the changes in extracellular concentration of potassium ions [K+]e and the negative DC shifts produced by stimulation of muscle, cutaneous and mixed afferent nerves, together with alterations in the threshold of single group Ia fibers that were tested at the same site as the potassium measurements. This approach provided information on the extent to which the excitability changes of single Ia-fibers can be correlated with the changes in [K+]e occurring at the same site. Stimulation of the tibial (TIB) nerve and of the cutaneous sural (SU), and superficial peroneous (SP) nerve (100-Hz trains lasting 30-60 s) with stimulus strengths of 10-15 times threshold increased the concentration of [K+]e in the dorsal horn by 2-5 mmol/l above the resting value of 3 mmol/l. This was in clear contrast with the very small [K+]e increases produced at the same site during stimulation of muscle nerves, such as the posterior biceps and semitendino...
The purpose of the present series of experiments was to analyze, in anesthetized and paralyzed ca... more The purpose of the present series of experiments was to analyze, in anesthetized and paralyzed cats, the effects of (-)-baclofen and picrotoxin on the primary afferent depolarization (PAD) generated in single Ib afferent fibers by either intraspinal microstimulation or stimulation of the segmental and descending pathways. PAD was estimated by recording dorsal root potentials and by measuring the changes in the intraspinal activation threshold of single Ib muscle afferent fibers. The PAD elicited by stimulation of group I muscle or cutaneous afferents was readily depressed and often abolished 20-40 min after the intravenous injection of 1-2 mg/kg (-)-baclofen. In contrast, the same amounts of (-)-baclofen produced a relatively small depression of the PAD elicited by stimulation of the brainstem reticular formation (RF). The monosynaptic PAD produced in single Ib fibers by intraspinal microstimulation within the intermediate nucleus was depressed and sometimes abolished following the i.v. injections of 1-2 mg/kg (-)-baclofen. Twenty to forty minutes after the i.v. injection of picrotoxin (0.5-1 mg/kg), there was a strong depression of the PAD elicited by stimulation of muscle and cutaneous afferents as well as of the PAD produced by stimulation of the RF and the PAD produced by intraspinal microstimulation. The results obtained suggest that, in addition to its action on primary afferents, (-)-baclofen may depress impulse activity and/or transmitter release in a population of last-order GABAergic interneurons that mediate the PAD of Ib fibers. The existence of GABAb autoreceptors in last-order interneurons mediating the PAD may function as a self-limiting mechanism controlling the synaptic efficacy of these interneurons.
2015) A machine learning methodology for the selection and classification of spontaneous spinal c... more 2015) A machine learning methodology for the selection and classification of spontaneous spinal cord dorsum potentials allows disclosure of structured (non-random) changes in neuronal connectivity induced by nociceptive stimulation.
1. In the anesthetized and artificially ventilated cat, stimulation of the posterior articular ne... more 1. In the anesthetized and artificially ventilated cat, stimulation of the posterior articular nerve (PAN) with low strengths (1.2-1.4 x T) produced a small negative response (N1) in the cord dorsum of the lumbosacral spinal cord with a mean onset latency of 5.2 ms. Stronger stimuli (> 1.4 x T) produced two additional components (N2 and N3) with longer latencies (mean latencies 7.5 and 15.7 ms, respectively), usually followed by a slow positivity lasting 100-150 ms. With stimulus strengths above 10 x T there was in some experiments a delayed response (N4; mean latency 32 ms). 2. Activation of posterior knee joint nerve with single pulses and intensities producing N1 responses only, usually produced no dorsal root potentials (DRPs), or these were rather small. Stimulation with strengths producing N2 and N3 responses produced distinct DRPs. Trains of pulses were clearly more effective than single pulses in producing DRPs, even in the low-intensity range. 3. Cooling the thoracic spi...
... VS) and group Ia GS fibers ending in the ventral horn was studied in the lumbosacral spinal c... more ... VS) and group Ia GS fibers ending in the ventral horn was studied in the lumbosacral spinal cord of the cat anesthetized with ... 25). Identification of the GS motor nucleus was done by recording the field potentials produced by stimulation of the GS afferent nerves or monosynaptic ...
AND CONCLUSIONS 1. Latencies of presynaptic depolarization of group I muscle afferents and cutane... more AND CONCLUSIONS 1. Latencies of presynaptic depolarization of group I muscle afferents and cutaneous afferents have been reinvestigated in an attempt to define the minimal number of interneurons interposed in the pathways of the presynaptic depolarization. Intra-axonal records from individual afferents, records of dorsal root potentials, and measurements of changes in excitability of individual afferents were used for this purpose. Some of the animals were treated with 4-aminopyridine to facilitate transmission via neuronal pathways.
An analysis was made of effects of 0.1-1.0 mg/kg 4-aminopyridine (4-AP) i.v. on excitatory and in... more An analysis was made of effects of 0.1-1.0 mg/kg 4-aminopyridine (4-AP) i.v. on excitatory and inhibitory spinal reflex pathways in lightly anaesthetized or decerebrated cats. The effects appeared within the first minutes of the injection, reached maximum after about 10-15 min and remained stable during at least several hours. 4-AP enhanced the following synaptic actions on motoneurones: monosynaptic excitation from Ia afferents and descending tracts, disynaptic and polysynaptic excitation from group Ib, group II, cutaneous and high threshold muscle afferents, disynaptic inhibition from Ia and Ib afferents and recurrent and polysynaptic inhibition from different afferents. 4-AP also increased primary afferent depolarization and excitation of ascending tract cells by peripheral stimuli. In the case of the disynaptic inhibitory pathways it has been shown that 4-AP may enhance the excitation of the interposed interneurones but it also increases the action of these interneurones on the motoneurones; monosynaptic inhibition evoked in motoneurones by electrical stimulation of the axons of the inhibitory interneurones was used as a test response in these experiments. No indications were found of direct effects of 4-AP on excitability of afferent fibres or motoneurones to electrical stimuli. No systematic changes were either found in the membrane potential of motoneurones or in the duration of action potentials of these neurones or primary afferents. It is therefore concluded that small doses of 4-AP enhance synaptic transmission in the spinal cord by an action at a presynaptic level.
ABSTRACT We describe here an automatic selection method to retrieve spontaneous cord dorsum poten... more ABSTRACT We describe here an automatic selection method to retrieve spontaneous cord dorsum potentials from the spinal cord in the anesthetized cat. Previous studies have indicated that some of these potentials appear synchronized in several spinal segments and are generated by the activation of specific sets of dorsal horn neurons. Since their synchronization is affected in a characteristic manner by acute peripheral nerve and spinal lesions, as well as during capsaicin-induced skin inflammation, they can be used to describe the patterns of functional interconnectivity between specific sets of dorsal horn neurons, which makes them of potential clinical interest.
In the spinal cord of the anesthetized cat, we measured the changes in extracellular concentratio... more In the spinal cord of the anesthetized cat, we measured the changes in extracellular concentration of potassium ions [K+]e and the negative DC shifts produced by stimulation of muscle, cutaneous and mixed afferent nerves, together with alterations in the threshold of single group Ia fibers that were tested at the same site as the potassium measurements. This approach provided information on the extent to which the excitability changes of single Ia-fibers can be correlated with the changes in [K+]e occurring at the same site. Stimulation of the tibial (TIB) nerve and of the cutaneous sural (SU), and superficial peroneous (SP) nerve (100-Hz trains lasting 30-60 s) with stimulus strengths of 10-15 times threshold increased the concentration of [K+]e in the dorsal horn by 2-5 mmol/l above the resting value of 3 mmol/l. This was in clear contrast with the very small [K+]e increases produced at the same site during stimulation of muscle nerves, such as the posterior biceps and semitendino...
The purpose of the present series of experiments was to analyze, in anesthetized and paralyzed ca... more The purpose of the present series of experiments was to analyze, in anesthetized and paralyzed cats, the effects of (-)-baclofen and picrotoxin on the primary afferent depolarization (PAD) generated in single Ib afferent fibers by either intraspinal microstimulation or stimulation of the segmental and descending pathways. PAD was estimated by recording dorsal root potentials and by measuring the changes in the intraspinal activation threshold of single Ib muscle afferent fibers. The PAD elicited by stimulation of group I muscle or cutaneous afferents was readily depressed and often abolished 20-40 min after the intravenous injection of 1-2 mg/kg (-)-baclofen. In contrast, the same amounts of (-)-baclofen produced a relatively small depression of the PAD elicited by stimulation of the brainstem reticular formation (RF). The monosynaptic PAD produced in single Ib fibers by intraspinal microstimulation within the intermediate nucleus was depressed and sometimes abolished following the i.v. injections of 1-2 mg/kg (-)-baclofen. Twenty to forty minutes after the i.v. injection of picrotoxin (0.5-1 mg/kg), there was a strong depression of the PAD elicited by stimulation of muscle and cutaneous afferents as well as of the PAD produced by stimulation of the RF and the PAD produced by intraspinal microstimulation. The results obtained suggest that, in addition to its action on primary afferents, (-)-baclofen may depress impulse activity and/or transmitter release in a population of last-order GABAergic interneurons that mediate the PAD of Ib fibers. The existence of GABAb autoreceptors in last-order interneurons mediating the PAD may function as a self-limiting mechanism controlling the synaptic efficacy of these interneurons.
2015) A machine learning methodology for the selection and classification of spontaneous spinal c... more 2015) A machine learning methodology for the selection and classification of spontaneous spinal cord dorsum potentials allows disclosure of structured (non-random) changes in neuronal connectivity induced by nociceptive stimulation.
1. In the anesthetized and artificially ventilated cat, stimulation of the posterior articular ne... more 1. In the anesthetized and artificially ventilated cat, stimulation of the posterior articular nerve (PAN) with low strengths (1.2-1.4 x T) produced a small negative response (N1) in the cord dorsum of the lumbosacral spinal cord with a mean onset latency of 5.2 ms. Stronger stimuli (> 1.4 x T) produced two additional components (N2 and N3) with longer latencies (mean latencies 7.5 and 15.7 ms, respectively), usually followed by a slow positivity lasting 100-150 ms. With stimulus strengths above 10 x T there was in some experiments a delayed response (N4; mean latency 32 ms). 2. Activation of posterior knee joint nerve with single pulses and intensities producing N1 responses only, usually produced no dorsal root potentials (DRPs), or these were rather small. Stimulation with strengths producing N2 and N3 responses produced distinct DRPs. Trains of pulses were clearly more effective than single pulses in producing DRPs, even in the low-intensity range. 3. Cooling the thoracic spi...
... VS) and group Ia GS fibers ending in the ventral horn was studied in the lumbosacral spinal c... more ... VS) and group Ia GS fibers ending in the ventral horn was studied in the lumbosacral spinal cord of the cat anesthetized with ... 25). Identification of the GS motor nucleus was done by recording the field potentials produced by stimulation of the GS afferent nerves or monosynaptic ...
AND CONCLUSIONS 1. Latencies of presynaptic depolarization of group I muscle afferents and cutane... more AND CONCLUSIONS 1. Latencies of presynaptic depolarization of group I muscle afferents and cutaneous afferents have been reinvestigated in an attempt to define the minimal number of interneurons interposed in the pathways of the presynaptic depolarization. Intra-axonal records from individual afferents, records of dorsal root potentials, and measurements of changes in excitability of individual afferents were used for this purpose. Some of the animals were treated with 4-aminopyridine to facilitate transmission via neuronal pathways.
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Papers by P. Rudomín