Biomedical subjects

Rodolfo Delgado-Lezama

Publications and source records attributed to Rodolfo Delgado-Lezama.

6 recordsLinked to original sources

PubMed2006

Heterosynaptic modulation of the dorsal root potential in the turtle spinal cord in vitro.

In the somatosensory system, the flow of sensory information is regulated at early stages by presynaptic inhibition. Recent findings have shown that the mechanisms generating the primary afferent depolarization (PAD) associated with presynaptic inhibition are complex, with some components mediated by a non-spiking mechanism. How sensory inputs carried by neighbouring afferent fibres interact to regulate the generation of PAD, and thus presynaptic inhibition, is poorly known. Here, we investigated the interaction between neighbouring primary afferents for the generation of PAD in an in vitro preparation of the turtle spinal cord. To monitor PAD we recorded the dorsal root potential (DRP), while the simultaneous cord dorsum potential (CDP) was recorded to assess the population postsynaptic response. We found that the DRP and the CDP evoked by a primary afferent test stimulus was greatly reduced by a conditioning activation of neighbouring primary afferents. This depression had early and late components, mediated in part by GABAA and GABAB receptors, since they were reduced by bicuculline and SCH 50911 respectively. However, with the selective stimulation of C and Adelta fibres in the presence of TTX, the early and late depression of the DRP was replaced by facilitation of the GABAergic and glutamatergic components of the TTX-resistant DRP. Our findings suggest a subtle lateral excitatory interaction between primary afferents for the generation of PAD mediated by a non-spiking mechanism that may contribute to shaping of information transmitted by C and Adelta fibres in a spatially confined scale in analogy with the retina and olfactory bulb.

Action Potentials↗

PubMed2005

Synaptic release of serotonin induced by stimulation of the raphe nucleus promotes plateau potentials in spinal motoneurons of the adult turtle.

Serotonin (5-HT) is a major modulator of the CNS. In motoneurons recorded in slices of the spinal cord, 5-HT promotes plateau potentials mediated by the activity of low-threshold L-type calcium channels (CaV1.3). However, no direct evidence has shown that 5-HT actually promotes plateau potentials under physiological conditions. Here, we investigate how release of 5-HT induced by activation of the raphe nucleus modulates intrinsic properties of spinal motoneurons. We developed an integrated preparation of the brainstem left in continuity with the cervical segments of the spinal cord from adult turtles. Electrical stimulation of the raphe nucleus increased the excitability of motoneurons by decreasing the amplitude of the afterhyperpolarization following action potentials and by promoting plateau potentials. Antagonists of 5-HT2 receptors applied in the vicinity of motoneurons inhibited the facilitation of plateaus. In a slice preparation in which glutamatergic, GABAergic, and glycinergic ionotropic synaptic transmission was blocked, stimulation of the dorsolateral funiculus facilitated a plateau potential by promoting a voltage-sensitive persistent inward current. This effect was inhibited by the addition of antagonists for 5-HT2 receptors. Our study suggests that CaV1.3 channels are regulated by 5-HT released from raphe spinal synaptic terminals via 5-HT2 receptors.

Action Potentials↗

PubMed2004

N- and P/Q-type Ca2+ channels regulate synaptic efficacy between spinal dorsolateral funiculus terminals and motoneurons.

Ca2+ influx through voltage-gated Ca2+ channels mediates synaptic transmission at numerous central synapses. However, electrophysiological and pharmacological evidence linking Ca+ channel activity with neurotransmitter release in the vertebrate mature spinal cord is scarce. In the current report, we investigated in a slice preparation from the adult turtle spinal cord, the effects of various Ca+ channel antagonists on neurotransmission at terminals from the dorsolateral funiculus synapsing motoneurons. Bath application of tetrodotoxin or NiCl2 prevented the monosynaptic excitatory postsynaptic potentials (EPSPs), and this effect was mimicked by exposure to a zero-Ca2+ solution. Application of polypeptide toxins that block N- and P/Q-type channels (omega-CTx-GVIA and omega-Aga-IVA) reduced the EPSP amplitude in a dose-dependent manner. By analyzing the input resistance and the EPSP time course, and using a paired pulse protocol we determined that both toxins act at presynaptic level to modulate neurotransmitter release. RT-PCR studies showed the expression of N- and P/Q-type channel mRNAs in the turtle spinal cord. Together, these results indicate that N- and P/Q-type Ca2+ channels may play a central role in the regulation of neurotransmitter release in the adult turtle spinal cord.

Animals↗

PubMed2003

Synaptic strength between motoneurons and terminals of the dorsolateral funiculus is regulated by GABA receptors in the turtle spinal cord.

The role of GABAA and GABAB receptors in modulation of excitatory synaptic transmission between motoneurons and terminals from dorsolateral funiculus (DLF) was studied in in vitro spinal cord slices of adult turtles. Muscimol--a GABAA receptor agonist--depressed the monosynaptic excitatory postsynaptic potential (EPSP) induced by stimulation of the DLF and shortened its duration. The input resistance and the membrane time constant also were strongly reduced. The input membrane resistance, the amplitude, and the half-width of the EPSP were reduced at the same rate in the presence of muscimol. Bicuculline--a GABAA receptor antagonist--increased the EPSPs amplitude and the input membrane resistance. The EPSP amplitude ratio elicited by a paired-pulse protocol did not change significantly. Our results suggest that muscimol acts mainly by activation of postsynaptic GABAA receptors located on the motoneuron and the synaptic strength on motoneurons may be modulated by tonic activation of postsynaptic GABAA receptors. Baclofen--a GABAB receptor agonist--also depressed DLF-motoneuron synaptic transmission. However, it did not affect the falling phase of the EPSPs or the motoneuron membrane time constant but induced a small decrement in input resistance. In the presence of baclofen, the amplitude ratio produced by a paired-pulse protocol increased significantly. This suggests that baclofen decreased the synaptic strength by inhibition of neurotransmitter release from the DLF terminals via activation of presynaptic GABAB receptors.

Animals↗

PubMed2003

A numeric study of the noise-induced tremor in a mathematical model of the stretch reflex.

A mathematical model of the stretch reflex for the cat soleus muscle is presented. The time-delay differential equations of the model are solved using the fourth-order Runge-Kutta algorithm, introducing a Gaussian-noise term to simulate the environmental noise. The muscle response dynamics are then studied under various levels of average muscle activation. Finally, the feasibility of explaining the so-called physiological tremor from the properties of the stretch reflex mechanisms is discussed by comparing our results with reported experimental evidence.

Animals↗

PubMed2002

Sustained firing of alpha and gamma hind limb motoneurons induced by stimulation of the pudendal nerve.

Axons from receptors in the cat vaginal wall run in the sensory pudendal nerve (SPN), and brief (<10 s) vaginal probing (VP) in the decerebrate cat produces a long-lasting (>1 min) contraction of the triceps surae (TS) muscles. The aim of the present project was to find out whether brief SPN stimulation also produces sustained TS response and, eventually, to study the mechanisms involved in it. Decerebrate female cats were used. In some cats, TS electromyography (EMG) and tension response were recorded; stimulation of left SPN with single or repetitive trains of shocks produced a bilateral TS response that outlasted the stimulus >1 min as VP did. In paralyzed cats (pancuronium; Panc), intracellular recordings were made from hind limb motoneurons (MNs). SPN stimulation produced a depolarization 1 min) electroneurographic (ENG) postdischarge in a small filament of the medial gastrocnemius (MG) nerve; the MG EMG postdischarge was also recorded. Large spikes (LS) and small spikes (SS) were distinguished in the ENG. During the postdischarge, LS frequency and the integrated EMG activity correlated well (r > 0.9); no correlation was found between SS and EMG. After Panc injection, LS postdischarge was absent but the SS postdischarge remained. LS followed by EMG potential were also evoked by brief TS stretch (reflex LS); single shocks to SPN only elicited SS that were not followed by EMG potential. It is concluded that alpha axons and gamma axons produced LS and SS, respectively, and that SPN activates gamma axons. It is proposed that, in the nonparalyzed cats, the stimulation of SPN with trains of shocks might cause an increase in the afferent inflow from muscle spindles to alpha MNs through the sustained firing of gamma MNs. The increased excitatory inflow would depolarize alpha MNs and allow bistable MN firing; Panc would decrease this inflow by blocking transmission to the spindle fibers.

Action Potentials↗