Physilogy and morphology of substantia gelatinosa neurons intracellularly stained with horserdish peroxidase

Abstract

Neurons in Rexed's layer II were physiologically characterized with natural and electrical stimuli applied to their cutaneous receptive fields. The neurons were then intracellularly stained with horseradish peroxidase. Three general patterns of physiological responses were found. Nociceptive specific neurons did not respond to gentle mechanical stimulation. Most responded exclusively to tissue-damaging stimuli. Some also responded to moderately heavy pressure, but these responded to noxious stimuli with an increased discharge frequency. Wide dynamic range neurons responded to both gentle mechanical stimulation and to tissue-damaging stimulation. Low-threshold mechanoreceptive neurons responded only to gentle mechanical stimulation. Some of the low-threshold mechanoreceptive neurons were innervated by primary afferents with unmyelinated axons. Excepting those low-threshold mechanoreceptive neurons with input from unmyelinated afferents, the patterns of primary afferents innervation of layer II neurons were similar to the patterns of innervation that have been found for neurons in layers I and IV-V. All but 2 of the 22 neurons that we found were recognized as being of two general morphological types. Stalked cells had their perikarya situated along the superficial border of layer II. Most of their dendrites traveled ventrally while spreading out rostrocaudally. This gave their dendritic arbors a fan-like shape. Stalked cell axons arborized largely in layer I. Islet cell perikarya were found throughout layer II. Most of their dendrites traveled rostrocaudally. Their dendritic arbors were shaped like cylinders with their long axes parallel to the long axis of the spinal cord. Islet cell axons arborized in the immediate vicinity of their dendritic territories, within layer II. Stalked cells and those islet cells whose dendritic arbors were largely contained within the superficial one-third of layer II (layer IIa) were either nociceptive specific or wide dynamic range neurons. The islet cells whose dendritic arbors were largely within the deeper two-thirds of layer II (layer IIb) were all low-threshold mechanoreceptive neurons. These observations suggest that layers IIa and IIb have different functional roles and that stalked cells and islet cells are separate and distinct components of the neural circuitry of the superficial dorsal horn.

Induction of Fos protein expression in spinal cord neurons of tumour-bearing rats

“…The observed localization of Fos-like immunoreactive neurons in tumour-bearing rats would best fit the pattern observed in monoarthritic rats (LanteriMinet et al, 1993) even if the time-courses differ. In tumourbearing rats, the detection of Fos labelling in nociceptive responding areas (Besson and Chaouch, 1987) is not in conflict with our previous suggestions since these areas are not specific for pain (Bennet et al, 1980;Menetrey, 1987). Thus, the presence of a tumoural process provokes functional alterations in spinal cord activity, demonstrating that a tumour actively proliferating in the limb sends afferent signals to the central nervous system, signals which are probably unrelated to pain.…”

Transneuronal Labeling of a Nociceptive Pathway, the Spino-(Trigemino-)Parabrachio-Amygdaloid, in the Rat

“…Double labeling of trigeminal ganglion neurons for PRV and substance P suggests that these lamina I projection neurons are acted on by peptide-containing nociceptive primary afferents, consistent with recent reports (Ding et al, 1995a,b) demonstrating that some lamina I neurons that project to the parabrachial complex express the substance P receptor. Although we could not discern the morphology of the lamina II neurons, some presumably correspond to the stalk cell, a proposed excitatory interneuron, the axon of which arborizes exclusively in lamina I (Bennett et al, 1980). On the other hand, because columns of cells were found throughout the depths of the substantia gelatinosa, it is likely that there was also labeling of the islet cells that populate the substantia gelatinosa.…”

Myelinated Skin Sensory Neurons Project Extensively throughout Adult Mouse Substantia Gelatinosa

“…Although exquisitely sensitive A␦ tactile afferents are present in human hairy skin nerves (Adriaensen et al, 1983) (but see Olausson et al, 2002;Cole et al, 2006), knowledge of their potential role in sensation is hampered by a lack of microstimulation studies. Nevertheless, substantial numbers of SG neurons respond well to light tactile stimuli, whether touch-specific or wide dynamic range neurons Bennett et al, 1980) (for review, see Light, 1992). Historically, while inhibition of nociceptive transmission by tactile inputs has received the most attention (Melzack and Wall, 1965) [see also Narikawa et al (2000) and Lu and Perl (2003)], recent studies suggest that most SG circuits are excitatory (Lu and Perl, 2005;Santos et al, 2007) and that incoming sensory information is relayed to neurons outside the SG (Giesler et al, 1978;Willis et al, 1978;Light, 1992;Eckert et al, 2003).…”