Serotonin modulates substance P-induced plasma extravasation and vasodilatation in rat skin by an action through capsaicin-sensitive primary afferent nerves

Spinal lamina II (substantia gelatinosa) neurons play an important role in processing of nociceptive information from primary afferent nerves. Anatomical studies suggest that neurons in the outer (lamina IIo) and inner (lamina IIi) zone of lamina II receive distinct afferent inputs. The functional significance of this preferential afferent termination in lamina II remains unclear. In this study, we examined the differential synaptic inputs to neurons in lamina IIo and IIi in response to primary afferent stimulation. Whole cell voltage-clamp recordings were performed on neurons in lamina IIo and IIi of the rat spinal cord slice under visual guidance. Capsaicin (1 μM) significantly increased the frequency of glutamatergic miniature excitatory postsynaptic currents (mEPSCs) in all 27 lamina IIo neurons and significantly increased the amplitude of mEPSCs in 12 of 27 lamina IIo neurons. However, capsaicin only significantly increased the frequency of mEPSCs in 9 of 22 (40.9%) lamina IIi neurons and increased the amplitude of mEPSCs in 6 of these 9 neurons. Furthermore, the peak amplitude of EPSCs, evoked by electrical stimulation of the attached dorsal root, in 40 lamina IIo neurons was significantly greater than that [160.5 ± 16.7 vs. 87.0 ± 10.4 (SE) pA] in 37 lamina IIi neurons. On the other hand, the peak amplitude of evoked inhibitory postsynaptic currents (IPSCs) in 40 lamina IIo neurons was significantly smaller than that (103.1 ± 11.6 vs. 258.4 ± 24.4 pA) in 37 lamina IIi neurons. In addition, the peak amplitudes of both EPSCs and IPSCs, evoked by direct stimulation of lamina II, were similar in lamina IIo and IIi neurons. This study provides new information that stimulation of primary afferents differentially potentiates synaptic inputs to neurons in lamina IIo and IIi. The quantitative difference in excitatory and inhibitory synaptic inputs to lamina IIo and IIi neurons may be important for integration of sensory information from primary afferent nerves.

Download Full-text

Interaction between primary afferent nerves in the elicitation of reflex swallowing

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1980.239.5.r407 ◽

1980 ◽

Vol 239 (5) ◽

pp. R407-R414 ◽

Cited By ~ 2

Author(s):

A. Weerasuriya ◽

D. Bieger ◽

C. H. Hockman

Keyword(s):

Contralateral Side ◽

Afferent Nerve ◽

Reflex Response ◽

Solitary Tract ◽

Primary Afferent ◽

Afferent Nerves ◽

Primary Afferent Nerves ◽

Adult Cats ◽

Primary Afferent Nerve ◽

Stimulation Of

In adult cats anesthetized with urethan, a number of observations were made that support the concept that some control over the rate of reflexly induced swallowing occurs in the intermediate network at the level of the nucleus of the solitary tract. It was shown that different nerves, e.g., the two superior laryngeal and glossopharyngeal nerves, when activated in sequence interact in such a manner as to facilitate reflex swallowing. It was also shown that the decrement in the reflex response observed to continuous stimulation of a primary afferent nerve, e.g., one superior laryngeal, can be reversed by switching the stimulation to another nerve either on the same or contralateral side. And finally, following discrete medullary lesions, it was observed that that portion of the nucleus of the solitary tract located 2 mm or more rostral to the rostralmost point of the dorsal medial sulcus appears to contain an integral component of the intermediate network that governs reflexly induced swallowing, whereas lesions restricted to the ventrolateral portion of the nucleus of the solitary tract have no effect on the reflex response.

Download Full-text