Showing papers on "Cuneate nucleus published in 2002"

Tracing of projection neurons from the cervical dorsal horn to the medulla with the anterograde tracer biotinylated dextran amine.

Abstract: In addition to the well-defined role of dorsal horn neurons in pain transmission, neurons in the superficial laminae also provide a rich source of synaptic input to cardiovascular and respiratory centers in the medullary reticular formation. In this study, ascending projection neurons from the superficial laminae of the cervical enlargement were studied in the rat using the anterograde tracer biotinylated dextran amine (BDA). Ipsilateral microinjection of BDA into the cervical spinal cord (C6–C8) resulted in extensive labeling of dorsal horn neurons in laminae I–V. Axons and terminal processes of cervical dorsal horn cells projecting to the medulla were present in the cuneate nucleus (Cu), the nucleus of the solitary tract (NTS), the lateral reticular nucleus, (LRt) as well as the caudal and rostral ventrolateral medulla (VLM). The highest density of BDA labeling was found ipsilaterally in the Cu, LRt, caudal and rostral VLM, while a moderate density of labeling was present in the NTS caudal to the area postrema (AP). Moderate-to-weak labeling was also found in the LRt, the caudal and rostral VLM contralateral to the BDA injection. These results support the existence of a spinomedullary pathway that transmits noxious and innocuous Aδ and C fiber-mediated sensory signals to the medulla. Neurons in this ascending spinal pathway likely participate in the patterning of autonomic responses evoked by pain or during exercise.

The lemniscal-cuneate recurrent excitation is suppressed by strychnine and enhanced by GABAA antagonists in the anaesthetized cat.

Abstract: In the somatosensory system, cuneolemniscal (CL) cells fire high frequency doublets of spikes facilitating the transmission of sensory information to diencephalic target cells. We studied how lemniscal feedback affects ascending transmission of cutaneous neurons of the middle cuneate nucleus. Electrical stimulation of the contralateral medial lemniscus and of the skin at sites evoking responses with minimal threshold induced recurrent activation of CL cells at a latency of 1-3.5 ms. The lemniscal feedback activation was suppressed by increasing the stimulating intensity at the same sites, suggesting recurrent-mediated lateral inhibition. The glycine antagonist strychnine blocked the recurrent excitatory responses while GABAA antagonists uncovered those obscured by stronger stimulation. CL cells sharing a common receptive field (RF) potentiate one another by recurrent activation and disinhibition, the disinhibition being produced by serial interactions between glycinergic and GABAergic interneurons. Conversely, CL cells with different RFs inhibit each other through recurrent GABA-mediated inhibition. The lemniscal feedback would thus enhance the surround antagonism of a centre response by increasing the spatial resolution and the transmission of weak signals.

Changes in c-Fos protein expression in the rat cuneate nucleus after electric stimulation of the transected median nerve.

Abstract: In this study we investigate temporal changes in Fos expression in cuneate neurons after a high-threshold electrical stimulation of the transected median nerve in rats. Two hours after injury of the median nerve when given electrical stimulation, c-Fos-immunoreactive (c-Fos-IR) cells were barely detected in the ipsilateral cuneate nucleus (CN). A few c-Fos-IR cells, however, were observed in the ipsilateral CN at 5 days. A marked increase in c-Fos-IR cells was observed at 2, 3, and 4 weeks, but levels subsided thereafter. Labeled cells were totally diminished by 16 weeks. The statistical analysis showed that the mean density of c-Fos-IR cells throughout the CN at 4 weeks was significantly higher than at other post-surgical time points, except for 3 weeks. Furthermore, the mean density of c-Fos-IR cells in the middle region of the CN was markedly higher than in other areas of the nucleus. The mean density of c-Fos-IR cells in the middle region at 4 weeks (mean density = 35.9 ± 3.0 cells/section) was consid...

Neurogenesis of cuneothalamic neurons and NO-containing neurons in the cuneate nucleus of the rat

Abstract: The genesis of the cuneothalamic neurons (CTNs) in the rat cuneate nucleus was determined by a double-labeling method using 5′-bromodeoxyuridine (BrdU), the thymidine analogue, and Fluoro-Gold (FG), a retrograde fluorescent tracer. BrdU-positive cells were observed in the cuneate nucleus in all rats receiving BrdU injection at embryonic days (E) E13–E16; none was detected in rats given BrdU injection at E12. At E13 and E14, BrdU-positive cells were randomly distributed. However, at E15, the number of BrdU-positive cells was clearly reduced and the majority of them was located at the dorsolateral or peripheral region of the nucleus. FG/BrdU double-labeling study showed the existence of BrdU-labeled CTNs when the mother rat received BrdU injection at E13 and E14, being more numerous at E13 in which the neurons were scattered throughout the nucleus. At E14, however, the majority of the BrdU-labeled CTNs were located superficially in the nucleus. Double-labeled cells were undetected in rats that had been exposed to BrdU at E15 and E16. Quantitative data showed that the majority (ca 70–80%) of the CTNs were generated at E13, and were markedly decreased at E14 (ca 4–6%). Using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry coupled with BrdU immunohistochemistry, we have shown the NADPH-d/BrdU double-labeled neurons in the nucleus between E13 and E15, with the majority of them occurring at E14, but absent at E16. The present results suggest that the CTNs are generated prior to the NO-containing neurons in the cuneate nucleus.

Edge Detection and Motion Discrimination in the Cuneate Nucleus

Abstract: In this paper we investigate how the cuneate nucleus could perform edge detection as well as motion discrimination by means of a single layer of multi-threshold cuneothalamic neurons. A well-known center-surround receptive field organization is in charge of edge detection, whereas single neuronal processing integrates inhibitory and excitatory inputs over time to discriminate dynamic stimuli. The simulations show how lateral inhibition determines a sensitized state in neighbouring neurons which respond to dynamic patterns with a burst of spikes.

Localization of glutamate receptor 2/3 subtypes in the rat nervous system

Abstract: The localization and distribution of glutamate receptor 2/3 subtypes (GluR2/3) in the rat nervous system was investigated by immunocytochemical staining technique. Intensely and densely stained GluR2/3 immunoreative neuronal cell bodies were observed in the cerebral cortex,caudate putaman,globus pallidus,septal nucleus, CA1 CA4 fields of the hippocampus,dentate gyrus, mammillary body, Purkinje cell layer of the cerebellum, oculomotor nucleus,trochlear nucleus,parabranchial nucleus,trigeminal motor nucleus,superior olivary complex,spinal trigeminal nucleus,facial nucleus,ambiguus nucleus,dorsal motor nucleus of vagus,hypoglossal nucleus,cuneate nucleus,gracile nucleus,laminae I and Ⅱ of the medullary and spinal dorsal horns,dorsal root ganglion, trigeminal ganglion, etc.The present results indicate that GluR2/3 are widely distributed in the rat nervous system, and glutamate might exert its principal excitatory effects through binding on these receptors. \[