Showing papers on "Cuneate nucleus published in 2004"

Primary afferent terminal sprouting after a cervical dorsal rootlet section in the macaque monkey.

Abstract: We examined the role of primary afferent neurons in the somatosensory cortical "reactivation" that occurs after a localized cervical dorsal root lesion (Darian-Smith and Brown [2000] Nat. Neurosci. 3:476-481). After section of the dorsal rootlets that enervate the macaque's thumb and index finger (segments C6-C8), the cortical representation of these digits was initially silenced but then re-emerged for these same digits over 2-4 postlesion months. Cortical reactivation was accompanied by the emergence of physiologically detectable input from these same digits within dorsal rootlets bordering the lesion site. We investigated whether central axonal sprouting of primary afferents spared by the rhizotomy could mediate this cortical reactivation. The cortical representation of the hand was mapped electrophysiologically 15-25 weeks after the dorsal rootlet section to define this reactivation. Cholera toxin subunit B conjugated to horseradish peroxidase was then injected into the thumb and index finger pads bilaterally to label the central terminals of any neurons that innervated these digits. Primary afferent terminal proliferation was assessed in the spinal dorsal horn and cuneate nucleus at 7 days and 15-25 postlesion weeks. Labeled terminal bouton distributions were reconstructed and the "lesion" and control sides compared within each monkey. Distributions were significantly larger on the side of the lesion in the dorsal horn and cuneate nucleus at 15-25 weeks after the dorsal rootlet section, than those mapped only 7 days postlesion. Our results provide direct evidence for localized sprouting of spared (uninjured) primary afferent terminals in the dorsal horn and cuneate nucleus after a restricted dorsal root injury.

Intracuneate mechanisms underlying primary afferent cutaneous processing in anaesthetized cats.

Abstract: The cutaneous primary afferents from the upper trunk and forelimbs reach the medial cuneate nucleus in their way towards the cerebral cortex. The aim of this work was twofold: (i) to study the mechanisms used by the primary afferents to relay cutaneous information to cuneate cuneolemniscal (CL) and noncuneolemniscal (nCL) cells, and (ii) to determine the intracuneate mechanisms leading to the elaboration of the output signal by CL cells. Extracellular recordings combined with microiontophoresis demonstrated that the primary afferent cutaneous information is communicated to CL and nCL cells through AMPA, NMDA and kainate receptors. These receptors were sequentially activated: AMPA receptors participated mainly during the initial phase of the response, whereas kainate- and NMDA-mediated activity predominated during a later phase. The involvement of NMDA receptors was confirmed by in vivo intracellular recordings. The cutaneous-evoked activation of CL cells was decreased by GABA and increased by glycine acting at a strychnine-sensitive site, indicating that glycine indirectly affects CL cells. Two subgroups of nCL cells were distinguished based on their sensitivity to iontophoretic ejection of glycine and strychnine. Overall, the results support a model whereby the primary afferent cutaneous input induces a centre-surround antagonism in the cuneate nucleus by activating (via AMPA, NMDA and kainate receptors) and disinhibiting (via serial glycinergic-GABAergic interactions) a population of CL cells with overlapped receptive fields that at the same time inhibit (via GABAergic cells) other neighbouring CL cells with different receptive fields.

Morphological Study on the Afferent Pathways of “Hegu” Point and Mouth-face Region

Abstract: Objective: To investigate the afferent pathways and the relationship between mouth-face region and “Hegu” (LI 4) Point. Methods: ① Biotin labeling: Twenty-four adult Wistar rats, divided into facial area and “Hegu” groups, were anesthetized with 1% sodium phentobarbital 40 mg/kg. Neurobiotin (Nb)(2.0%, 20 μL) was injected into the left mouth-face and “Hegu”(LI 4) point regions respectively.72 hours later, these animals under anesthesia were perfused transcardially with saline, then with fixative (1.5% glutaraldehyde and 1.0% paraformaldehyde in 0.1 M sodium phosphate buffer). ② Expression of c-fos: 24 Wistar rats were divided into facial area and “Hegu” groups. Under anesthesia, the left mouth-face and “Hegu” were punctured with acupuncture needles (with two needles being in each point) and stimulated with an electroacupuncture apparatus by setting the stimulating parameters as strength of 5 V, frequency of 100 Hz and duration of 30 min. 1.5～2 hours later, the rats were perfused with the same fixative mentioned above. Spinal cord and lower-brainstem tissues were sliced (30 μm) and then stained with immunohistochemical method. Results: ① Following injection of biotin into facial area, densely labeled fibers were found in the left nucleus of spinal tract of trigeminal nerve (NSTTN) and semilunar ganglion of the trigeminal nerve; light-densely labeled fibers observed in nucleus of the solitary tract (NTS) and reticular formation, and fewer positive fibers seen in the posterior horn of C 1～C 3 of the spinal cord.② The densely labeled fibers from “Hegu” (LI 4) area were found in the posterior horn of C 6, moderate amount of the labeled fibers were seen in C 4～C 5, and fewer seen in cuneate nucleus of the medulla oblongata. ③ After EA stimulation of the left facial area, a large number of fos positive neurons were observed in the ipsilateral NSTTN, moderate number of the labeled cells seen in semilunar ganglion of the trigeminal nerve, NTS and reticular formation of the medulla oblongata, and fewer c-fos positive cells seen in the ipsilateral posterior horn of C 1～C 3 segments. ④ Following EA stimulation of “Hegu”(LI 4), many c-fos positive neurons were observed in the posterior horn of C 4～C 6, and fewer labeling was seen in cuneate nucleus, NTS and reticular formation of the medulla oblongata. Conclusion: Facial area may have a direct connection with NTS, while “Hegu” point has no direct project to NTS, nevertheless, message of EA of “Hegu” may reach NTS by way of secondary afferent neurons, etc. In short, NTS may play an important role in the integration and convergence of information from the facial area and “Hegu” point.