Interaction between neurons in different laminae of the dorsal horn of the spinal cord. A correlation study in normal and neuropathic rats.
ABSTRACT Simultaneous recordings of 135 pairs of units, located respectively in the superficial (I-IIo) and deep (V) laminae of the dorsal horn of the lumbar spinal cord of anaesthetized and paralysed animals, were performed both from normal (62 pairs) and from peripherally injured (chronically constricted sciatic nerve) rats (73 pairs). In each pair, one neuron was classified as nociceptive, responding only to noxious stimuli, and the other as a wide dynamic range neuron, responding to both non-noxious and noxious stimuli. To understand if some interaction was present between diverse neurons modulated by noxious inputs, we used cross-correlation techniques. The responses of simultaneously recorded pairs of units to suprathreshold (5 mA, 0.5 ms) electrical stimuli were used. A clearly delayed peak in the cross-correlograms of recordings from normal animals was present, indicating connectivity of superficial and deep-layer cells. This feature was not present in the cross-correlograms obtained from nerve-injured animals. Even if a specific pathway cannot be explicitly assigned to support these functional results, an overall connection between superficial and deep layers of the spinal cord is suggested. These connections are supposed to be either inactive or rearranged in the nerve-injured rats, thus suppressing a well timed coordinated connectivity. This anomaly could underlie a reduced degree of functional coherence in the modulation of nociceptive spinal inputs in cases of chronic pain.
- SourceAvailable from: Majid Sheykhzade[Show abstract] [Hide abstract]
ABSTRACT: The aim of the present study was to examine spinal processing of cardiac and somatic nociceptive input in rats with STZ-induced diabetes. Type 1 diabetes was induced with streptozotocin (50mg/kg) in 14 male Sprague-Dawley rats and citrate buffer was injected in 14 control rats. After 4-11 weeks, the rats were anesthetized with pentobarbital, ventilated and paralyzed. A laminectomy enabled extracellular recording of T(3) spinal cord neuronal activity. Intrapericardial administration of a mixture of algogenic chemicals (bradykinin, serotonin, prostaglandin E(2) (all at 10(-5)M), and adenosine (10(-3)M)) was applied to activate nociceptors of cardiac afferent nerve endings. Furthermore, somatic receptive properties were examined by applying innocuous (brush and light pressure) and noxious (pinch) cutaneous mechanical stimuli. Diabetes-induced increases in spontaneous activity were observed in subsets of neurons exhibiting long-lasting excitatory responses to administration of the algogenic mixture. Algogenic chemicals altered activity of a larger proportion of neurons from diabetic animals (73/111) than control animals (55/115, P<0.05). Some subtypes of neurons exhibiting long-lasting excitatory responses, elicited prolonged duration and others, had a shortened latency. Some neurons exhibiting short-lasting excitatory responses in diabetic animals elicited a shorter latency and some a decreased excitatory change. The size of the somatic receptive field was increased for cardiosomatic neurons from diabetic animals. Cutaneous somatic mechanical stimulation caused spinal neurons to respond with a mixture of hyper- and hypoexcitability. In conclusion, diabetes induced changes in the spinal processing of cardiac input and these might contribute to cardiovascular autonomic neuropathy in patients with diabetes.Autonomic neuroscience: basic & clinical 08/2011; 165(2):168-77. · 1.82 Impact Factor
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ABSTRACT: Simultaneous recordings of cord dorsum potentials along the lumbo-sacral spinal cord of the anaesthetized cat revealed the occurrence of spontaneous synchronous negative (n) and negative-positive (np) cord dorsum potentials (CDPs). The npCDPs, unlike the nCDPs, appeared preferentially associated with spontaneous negative dorsal root potentials (DRPs) resulting from primary afferent depolarization. Spontaneous npCDPs recorded in preparations with intact neuroaxis or after spinalization often showed a higher correlation than the nCDPs recorded from the same pair of segments. The acute section of the sural and superficial peroneal nerves further increased the correlation between paired sets of npCDPs and reduced the correlation between the nCDPs recorded from the same pair of segments. It is concluded that the spontaneous nCDPs and npCDPs are produced by the activation of interconnected sets of dorsal horn neurones located in Rexed's laminae III–IV and bilaterally distributed along the lumbo-sacral spinal cord. Under conditions of low synchronization in the activity of this network of neurones there would be a preferential activation of the intermediate nucleus interneurones mediating Ib non-reciprocal postsynaptic inhibition. Increased synchronization in the spontaneous activity of this ensemble of dorsal horn neurones would recruit the interneurones mediating primary afferent depolarization and presynaptic inhibition and, at the same time, reduce the activation of pathways mediating Ib postsynaptic inhibition. Central control of the synchronization in the spontaneous activity of dorsal horn neurones and its modulation by cutaneous inputs is envisaged as an effective mechanism for the selection of alternative inhibitory pathways during the execution of specific motor or sensory tasks.The Journal of Physiology 01/2012; 590(Pt 7):1563-84. · 4.38 Impact Factor
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ABSTRACT: In acute rat spinal cord slices, the application of capsaicin (5 μm, 90 s), an agonist of transient receptor potential vanilloid 1 receptors expressed by a subset of nociceptors that project to laminae I-II of the spinal cord dorsal horn, induced an increase in the frequency of spontaneous excitatory and spontaneous inhibitory postsynaptic currents in about half of the neurons in laminae II, III-IV and V. In the presence of tetrodotoxin, which blocks action potential generation and polysynaptic transmission, capsaicin increased the frequency of miniature excitatory postsynaptic currents in only 30% of lamina II neurons and had no effect on the frequency of miniature excitatory postsynaptic currents in laminae III-V or on the frequency of miniature inhibitory postsynaptic currents in laminae II-V. When the communication between lamina V and more superficial laminae was interrupted by performing a mechanical section between laminae IV and V, capsaicin induced an increase in spontaneous excitatory postsynaptic current frequency in laminae II-IV and an increase in spontaneous inhibitory postsynaptic current frequency in lamina II that were similar to those observed in intact slices. However, in laminae III-IV of transected slices, the increase in spontaneous inhibitory postsynaptic current frequency was virtually abolished. Our results indicate that nociceptive information conveyed by transient receptor potential vanilloid 1-expressing nociceptors is transmitted from lamina II to deeper laminae essentially by an excitatory pathway and that deep laminae exert a 'feedback' control over neurons in laminae III-IV by increasing inhibitory synaptic transmission in these laminae. Moreover, we provide evidence that laminae III-IV might play an important role in the processing of nociceptive information in the dorsal horn.European Journal of Neuroscience 09/2012; · 3.75 Impact Factor