texas-red and Pain

Thalamic intralaminar and medial nuclei participate mainly in affective and motivational aspects of pain processing. Unique to the present study were identification and characterization of spontaneously active neurons in the central lateral nucleus (CL) of the intralaminar thalamus, which were found to respond only to viscerally evoked noxious stimuli in animals under pentobarbital anesthesia. Responses to noxious colorectal distention, intrapancreatic bradykinin, intraperitoneal dilute acetic acid, and greater splanchnic nerve electrical stimulation were characterized. Electrophysiological recordings revealed activity in most CL neurons (93%) was excited (69%) or inhibited (31%) in response to noxious visceral stimulation of visceral nerves. Expression of c-Fos observed in CL nucleus after intensive visceral stimulation confirmed the activation. However, excited CL neurons did not have somatic fields, except in 3 of 43 (7%) CL neurons tested for responses to somatic stimulation (innocuous brush and noxious pinch). Intrathecal administration of morphine significantly reduced the increased responses of CL neurons to colorectal and pancreatic stimuli and was naloxone reversible. High-level thoracic midline dorsal column (DC) myelotomy also dramatically reduced responses, identifying the DC as a major route of travel from the spinal cord for CL input, in addition to input traveling ventromedially in the spinothalamic tract identified anatomically in a previous study. Spinal cord and lower brain stem cells providing input to medial thalamus were mapped after stereotaxic injections of a retrograde dye. These data combined with our previous data suggest that the CL nucleus is an important component of a medial visceral nociceptive system that may mediate attentional, affective, endocrine, motor, and autonomic responses to noxious visceral stimuli.

Topics: Action Potentials; Afferent Pathways; Animals; Bradykinin; Male; Morphine; Neural Inhibition; Neurons; Pain; Pancreatic Ducts; Physical Stimulation; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Thalamus; Vasodilator Agents; Viscera; Xanthenes

The expression of capsaicin (VR1) receptor by A-fiber primary afferent neurons has been investigated by double immunohistochemical staining with VR1 and 200 kD neurofilament (NF200; an A-fiber marker) antibodies, and by VR1 immunohistochemical staining in combination with cholera toxin B subunit (CTB; also an A-fiber marker) retrograde tracing. Approximately 30% of the VR1-positive dorsal root ganglion (DRG) neurons were NF200-positive. Intra-sciatic nerve injection of CTB labeled over 30% of the VR1-positive neurons in the L5 DRG. Size frequency distribution analysis revealed that these VR1 and NF200, or VR1 and CTB, double-labeled neurons were predominantly small and medium sized. These results suggest that capsaicin receptors are likely to be expressed by Adelta-fiber neurons as well as C-fiber neurons.

Topics: Animals; Cell Size; Cholera Toxin; Fluorescein-5-isothiocyanate; Fluorescent Antibody Technique; Fluorescent Dyes; Ganglia, Spinal; Nerve Fibers, Myelinated; Neurofilament Proteins; Neurons, Afferent; Nociceptors; Pain; Rats; Rats, Sprague-Dawley; Receptors, Drug; Synaptic Transmission; Xanthenes