RESUMEN
Recently it has been suggested that the neurohormone prolactin (PRL) could act on the afferent nociceptive neurons. Indeed, PRL sensitizes transient receptor potential vanilloid 1 (TRPV1) channels present in nociceptive C-fibers and consequently reduces the pain threshold in a model of inflammatory pain. Accordingly, high plasma PRL levels in non-lactating females have been associated with several painful conditions (e.g. migraine). Paradoxically, an increase of PRL secretion during lactation induced a reduction in pain sensitivity. This difference could be attributed to the fact that PRL secreted from the adenopituitary (AP) is transformed into several molecular variants by the suckling stimulation. In order to test this hypothesis, the present study set out to investigate whether PRL from AP of suckled (S) or non-suckled (NS) lactating rats affects the activity of the male Wistar wide dynamic range (WDR) neurons. The WDR neurons are located in the dorsal horn of the spinal cord and receive input from the first-order neurons (Ab-, Ad- and C-fibers). Spinal administration of prolactin variant from NS rats (NS-PRL) or prolactin variant from S rats (S-PRL) had no effect on the neuronal activity of non-nociceptive Ab-fibers. However, the activities of nociceptive Ad-fibers and C-fibers were: (i) increased by NS-PRL and (ii) diminished by S-PRL. Either NS-PRL or S-PRL enhanced the post-discharge activity. Taken together, these results suggest that PRL from S or NS lactating rats could either facilitate or depress the nociceptive responses of spinal dorsal horn cells, depending on the physiological state of the rats.
Asunto(s)
Lactancia/fisiología , Fibras Nerviosas/efectos de los fármacos , Nociceptores/fisiología , Células del Asta Posterior/fisiología , Prolactina/farmacología , Médula Espinal/citología , Animales , Femenino , Lactancia/sangre , Masculino , Fibras Nerviosas/fisiología , Nociceptores/efectos de los fármacos , Umbral del Dolor/efectos de los fármacos , Umbral del Dolor/fisiología , Células del Asta Posterior/efectos de los fármacos , Prolactina/sangre , Ratas , Ratas WistarRESUMEN
Long-term potentiation (LTP) can be induced by electrical stimulation and gives rise to an increase in synaptic strength at the first relay. This phenomenon has been associated with learning and memory and also could be the origin of several pathological states elicited by an initial strong painful stimulus, such as some forms of neuropathic pain. We used high-frequency electrical stimulation of the sciatic nerve in anesthetized rats to produce spinal LTP. To evaluate the effect of spinal LTP on the activity of neurons in the posterior triangular nucleus of the thalamus (PoT), we applied an electrical stimulation (40 stimuli; 1ms; 0.5Hz; 1.5mA) to cutaneous tissues at 10-min intervals during at least 3h. In the majority of cases, PoT cells did not respond to cutaneous stimulation before LTP, but 50min after LTP induction PoT cells progressively began responding to the cutaneous stimulation. Furthermore, after 3h of LTP induction, PoT neurons could respond to cutaneous stimulation applied to different paws. Interestingly, the conduction velocities for the receptive field responses from the paw to the PoT cells were compatible with those of Aδ-fibers. Since PoT cells project to the insular cortex, the progressive increase in PoT activity and also the progressive unmasking of somatic receptive fields in response to LTP, place these cells in a key position to detect pain stimuli following central sensitization.
Asunto(s)
Potenciación a Largo Plazo/fisiología , Nocicepción/fisiología , Nervio Ciático/fisiología , Médula Espinal/fisiología , Núcleos Talámicos/fisiología , Animales , Estimulación Eléctrica , Masculino , Neuronas/fisiología , Ratas , Factores de TiempoRESUMEN
Oxytocin (OT) secreted by the hypothalamo-spinal projection exerts antinociceptive effects in the dorsal horn. Electrophysiological evidence indicates that OT could exert these effects by activating OT receptors (OTR) directly on dorsal horn neurons and/or primary nociceptive afferents in the dorsal root ganglia (DRG). However, little is known about the identity of the dorsal horn and DRG neurons that express the OTR. In the dorsal horn, we found that the OTR is expressed principally in neurons cell bodies. However, neither spino-thalamic dorsal horn neurons projecting to the contralateral thalamic ventral posterolateral nucleus (VPL) and posterior nuclear group (Po) nor GABaergic dorsal horn neurons express the OTR. The OTR is not expressed in skin nociceptive terminals or in dorsal horn nociceptive fibers. In the DRG, however, the OTR is expressed predominantly in non-peptidergic C-fiber cell bodies, but not in peptidergic or mechanoreceptor afferents or in skin nociceptive terminals. Our results suggest that the antinociceptive effects of OT are mediated by direct activation of dorsal horn neurons and peripheral actions on nociceptive, non-peptidergic C-afferents in the DRG.
Asunto(s)
Ganglios Espinales/metabolismo , Neuronas/metabolismo , Nociceptores/metabolismo , Células del Asta Posterior/metabolismo , Receptores de Oxitocina/metabolismo , Animales , Péptido Relacionado con Gen de Calcitonina/metabolismo , Técnica del Anticuerpo Fluorescente , Colorantes Fluorescentes , Ganglios Espinales/citología , Procesamiento de Imagen Asistido por Computador , Interneuronas/metabolismo , Masculino , Fibras Nerviosas Amielínicas/metabolismo , Neuronas Aferentes/metabolismo , Núcleo Hipotalámico Paraventricular/metabolismo , Ratas , Ratas Wistar , Tractos Espinotalámicos/citología , Tractos Espinotalámicos/metabolismo , Estilbamidinas , Ácido gamma-Aminobutírico/fisiologíaRESUMEN
Simultaneous recordings of cortical evoked potentials in the posterior sigmoid gyrus, and spontaneous negative cord dorsum potentials (CDPs) of the L6 lumbar spinal segment, were made in the anaesthetised cat. The electrodes were positioned in cortical and spinal somatosensory regions where the largest spontaneous and evoked negative potentials were detected. Evoked potentials were produced by electrical stimulation to cutaneous nerves or by mechanical stimulation of the hindpaw skin. We found that both electrically and mechanically cortical evoked potentials were facilitated during the spontaneous negative CDPs. The magnitude of such facilitation was proportional to the amplitude of the 'conditioning' spontaneous negative CDPs. This led to a high positive correlation between amplitude fluctuations of spontaneous negative CDPs and fluctuations of the cortical evoked potentials. This observation suggests that transmission of cutaneous sensory information in ascending pathways could be facilitated when dorsal horn spinal neurones are active.
Asunto(s)
Vías Aferentes/fisiología , Potenciales Evocados Somatosensoriales/fisiología , Mecanorreceptores/fisiología , Nervios Periféricos/fisiología , Células del Asta Posterior/fisiología , Corteza Somatosensorial/fisiología , Potenciales de Acción/fisiología , Animales , Gatos , Estimulación Eléctrica , Conducción Nerviosa/fisiología , Estimulación Física , Transmisión Sináptica/fisiología , Tacto/fisiologíaRESUMEN
Simultaneous recordings of cortical activity, recorded as the cortical local field potential (CLFP) in the contralateral posterior sigmoid gyrus, and the spinal activity, recorded as the cord dorsum potential (CDP) of the L6 lumbar segment, were made in the anaesthetized cat. The electrodes were positioned in somatosensory regions where the largest spontaneous negative CLFPs and CDPs were recorded. We found that spontaneous negative CLFPs were preceded by spontaneous negative CDPs with a mean latency of 14.4+/-3.5 ms. Amplitude of these spontaneous negative CLFPs was abolished after section of the dorsal columns and ipsilateral dorsolateral funiculus. It is concluded that the neurones of the primary somatosensory cortex can be driven by dorsal horn spinal neurones producing the spontaneous negative CDPs. This suggests very strongly that spontaneous neuronal activity in somatosensory regions of the brain is generated not only by ongoing activity of neurones located at supraspinal sites, but also by ongoing activity of spinal neurones.
Asunto(s)
Potenciales de Acción/fisiología , Vías Aferentes/fisiología , Red Nerviosa/fisiología , Conducción Nerviosa/fisiología , Células del Asta Posterior/fisiología , Corteza Somatosensorial/fisiología , Transmisión Sináptica/fisiología , Animales , Axotomía , Gatos , Estimulación Eléctrica , Tacto/fisiologíaRESUMEN
A previous study has shown that lumbar spontaneous cord dorsum potentials (CDPs) are produced by background activity of a neuronal ensemble located in the dorsal horn. Here, the effects produced by intravenous application of the nitric oxide synthase inhibitor L-N(G)-nitro arginine (L-NOARG, 100 microg/kg) and of the nitric oxide donor 3-morpholinosydnonimine hydrochloride (SIN-1, 500 microg/kg) on spontaneous CDPs were examined. Experiments were performed on pentobarbitally anesthetized, paralyzed and spinalized cats. The amplitude of spontaneous CDPs increased after L-NOARG, however, decreased after SIN-1. These observations suggest that electrical activity of dorsal horn neurones generating spontaneous CDPs is dependent on nitric oxide production.
Asunto(s)
Potenciales de Acción/fisiología , Vías Nerviosas/enzimología , Óxido Nítrico Sintasa/metabolismo , Óxido Nítrico/biosíntesis , Células del Asta Posterior/enzimología , Potenciales de Acción/efectos de los fármacos , Animales , Gatos , Inhibidores Enzimáticos/farmacología , Molsidomina/análogos & derivados , Molsidomina/farmacología , NG-Nitroarginina Metil Éster/farmacología , Inhibición Neural/efectos de los fármacos , Inhibición Neural/fisiología , Vías Nerviosas/efectos de los fármacos , Óxido Nítrico/agonistas , Óxido Nítrico/antagonistas & inhibidores , Donantes de Óxido Nítrico/farmacología , Óxido Nítrico Sintasa/antagonistas & inhibidores , Células del Asta Posterior/efectos de los fármacosRESUMEN
In anesthetized rats it was tested whether or not the activity of the ON and OFF cells within the rostral ventromedial medulla (RVM) is modulated by the mechanical stimulation of the uterine cervix (VS). ON cells were identified by an abrupt increase in their firing rate before the tail flick in response to a noxious heat. OFF cells were identified by a sudden decrease in their firing rate before the tail flick. All (27 out of 27) identified ON cells decreased their firing rate immediately after VS was applied. The effect of VS on the activity of the cells persisted for the entire stimulation period. On the other hand, all (19 out of 19) identified OFF cells increased their firing rate immediately after VS. The effect of VS on the activity of these cells also persisted for the entire stimulation period. The activity of the neutral cells showed no change, neither during the application of noxious heat, nor during VS. These results suggest that the analgesic-like effect produced by VS can be mediated by the activity of the antinociceptive circuit at the RVM. Alternatively, it can be suggested that the afferent inflow from the genital tract can induce the activity of the antinociceptive circuit at RVM, either by projections to the periaqueductal gray matter or by direct projections to RVM.