Ultrastructural and immunocytochemical characterization of terminals of postsynaptic ascending dorsal column fibers in the rat cuneate nucleus

Abstract

The morphology, synaptic contacts, and neurotransmitter enrichment of postsynaptic dorsal column terminals in the cuneate nucleus of rats were investigated and compared with those of identified primary afferents. For this purpose, anterograde transport of horseradish peroxidase-based tracers injected in the spinal cord was combined with postembedding immunogold labeling for glutamate and gamma-aminobutyric acid (GABA). Anterogradely labeled postsynaptic dorsal column terminals were morphologically homogeneous: they were small (mean area = 1.37 microns 2) and dome-shaped, contacted single dendritic shafts or cell bodies, and were not involved in axoaxonic synapses. The majority of them were not enriched in glutamate or GABA immunoreactivity compared with other tissue components. Their morphology, size, and neurotransmitter content thus differed from that of primary afferents. These differences are consistent with distinct functional roles for the two main afferent systems ascending to the cuneate nucleus.

Cholinergic Modulation of Synaptic Transmission and Postsynaptic Excitability in the Rat Gracilis Dorsal Column Nucleus

“…Immunohistochemical studies in the rat show that DC and CF inputs to dorsal column nuclei are glutamatergic (Rustioni and Weinberg, 1989;Broman, 1994;DeBiasi et al, 1994) and that dorsal column nuclei neurons express both AMPA and NMDA receptors (Watanabe et al, 1994;Kus et al, 1995;Popratiloff et al, 1997). Consistent with those findings, we had reported that responses of GN neurons evoked by both DC and CF inputs were glutamatergic and that non-NMDA receptors mediate DCEPSPs, whereas CF-EPSPs also display an NMDA component Buño, 1999, 2001).…”

“…The gracilis nucleus (GN) of the dorsal column (DC) nuclei receives somatosensory information from the hindlimbs through afferents running in the dorsal columns (Nyberg and Blomqvist, 1982;Rustioni and Weinberg, 1989;DeBiasi et al, 1994). DC fibers are glutamatergic and contact both projecting neurons and inhibitory interneurons (Rustioni and Weinberg, 1989;Broman, 1994;DeBiasi et al, 1994).…”

“…DC fibers are glutamatergic and contact both projecting neurons and inhibitory interneurons (Rustioni and Weinberg, 1989;Broman, 1994;DeBiasi et al, 1994). Stimulation of the peripheral receptive field or electrical stimulation of the DC evokes EPSPs and IPSPs in dorsal column nucleus neurons in vivo (Andersen et al, 1964;Canedo et al, 1998).…”

Corticofugal Modulation of the Tactile Response Coherence of Projecting Neurons in the Gracilis Nucleus

“…The dorsal column nuclei (DCN), which include the gracilis and cuneate nuclei, are the first relay station in the lemniscal pathway that receives somatosensory information from the body through the dorsal column and projects to the somatosensory thalamus. DCN neurons receive two major excitatory synaptic inputs that control their activity: first, due to ascending somatosensory fibers by the dorsal column, which establish contact with both thalamic projection neurons and inhibitory interneurons (DeBiasi et al 1994;Lue et al 1996;Rustioni and Weinberg 1989); second, due to corticofugal fibers, primarily from cells in the forelimb and hindlimb regions of the primary somatosensory (SI) cortex and, to a lesser extent, from the secondary somatosensory cortical area, running mainly through the pyramidal tract (Jabbur and Towe 1961;Kuypers and Tuerk 1964;Valverde 1966;Weisberg and Rustioni 1976). The ascending pathway has been extensively studied over the last few decades (see e.g., DeBiasi et al 1994;Lue et al 1996;Rustioni and Weinberg 1989), whereas little is known about the role and dynamical properties of the corticofugal pathway.…”

Primary somatosensory cortex modulation of tactile responses in nucleus gracilis cells of rats

“…Electrical stimulation of the contralateral SI cortex can excite or inhibit the activity of DCN neurons (Towe & Jabbur, 1961; Gordon & Jukes, 1964; Lewitt et al ., 1964; Cheema et al ., 1983; Cole & Gordon, 1992; Malmierca & Nuñez, 1998). Peripheral and cortical inputs evoke excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs, respectively) in DCN neurons recorded in vivo (Andersen et al ., 1964a, 1964b; Schwartzkroin et al ., 1974; Canedo & Aguilar, 2000; Mariño et al ., 2000) and use glutamate as an excitatory neurotransmitter (Rustioni & Cuénod, 1982; Conti et al ., 1989; DeBiasi et al ., 1994). Histological studies in the rat have identified N ‐methyl‐D‐aspartate (NMDA) and non‐NMDA receptors in the DCN (Watanabe et al ., 1994; Kus et al ., 1995; Popratiloff et al ., 1997).…”