Effects of Conditioning Stimulation of the Central Amygdaloid Nucleus on Tooth Pulp-Driven Neurons in the Cat Somatosensory Cortex(SI).

Abstract

The sensation we call pain, like other sensations, can be modulated by exposure to a stressful situation such as a fight or athletic competition. It has been suggested that stress is a physiologic trigger of the intrinsic pain inhibitory system. This phenomenon has been termed as stress-induced analgesia (SIA) (see Amit and Galina [1] for review) or fear-induced analgesia [2]. Actually, acupuncture and transcutaneous electrical nerve stimulation, which might be considered stressful, have been used for analgesia as a clinical procedure [1]. However, the neuronal mechanism and anatomical substrates involved in SIA have remained unclear.It has been demonstrated that the central amygdaloid nucleus (ACE) has an integrative role for coordinating an organism's autonomic, endocrine, and behavioral responses to various stressful stimuli, and that electrical stimulation of the ACE can mimic several of the stress-like responses (see Glavin et al. [3] for review). Lesions of the ACE have been found to block cardiovascular, respiratory, and behavioral parameters of responses to stressors [4,5]. Intracere- Japanese Journal of Physiology, 49, 485-497, 1999 Key words: central amygdaloid nucleus, stress-induced antinociception, somatosensory cortex, tooth pulp-driven neuron, H 1 receptor. Abstract:To study the limbic control of nociception, we examined the effect of conditioning stimulation of the central amygdaloid nucleus (ACE) on tooth pulp-driven (TPD) neurons in the first somatosensory cortex (SI). Cats were anesthetized with N 2 O-O 2 (2 : 1) and 0.5% halothane, and immobilized with tubocurarine chloride. The tooth pulp test stimulus was applied by a single rectangular pulse (0.5 ms in duration and 3-5 times the threshold intensity for the jaw-opening reflex). Conditioning stimuli to the ACE consisted of trains of 33 pulses (300 A) delivered at 330 Hz at intervals of 8-10 s. In 35 out of 61 of the slow (S)-type TPD neurons with latencies of more than 20 ms, conditioning stimulation in the ACE, especially in the medial division, markedly reduced the firing response to the pulpal stimulation. The inhibition of the firing rate in the S-type neurons was 74% of the control. In these S-type neurons, the neurons that were inhibited had significantly longer latencies compared to the noninhibited neurons (45.0Ϯ17.6 ms, nϭ32 vs. 34.8Ϯ10.5 ms, nϭ26). In contrast, the ACE conditioning stimulation affected only one out of 18 fast-type TPD neurons with latencies of less than 20 ms. In addition, ACE stimulation had no effect on the spontaneous discharges of either S-type or F-type neurons. The ACE inhibitory effect on S-type neurons was not diminished by naloxone administration (1 mg/kg, I.V.), while the blockade of histamine H 1 -receptor by diphenhydramine hydrochloride (0.5 mg/kg, I.V.) partially reversed the inhibitory effect. These results suggest that the ACE inhibits ascending nociceptive information to the SI and that this inhibition is mediated in part by histamine (H 1 ) receptors. It seems likely that the antinociceptive ...

Sensory ability in the narwhal tooth organ system

“…This theory explains the known ability of teeth to sense environmental stimuli, and supports the evolutionary descriptions of tooth precursors as sensory organs (Lumsden, ). Human and other mammalian teeth are known to be capable of sensing external stimuli (Anderson, ; Haegerstam, ; Byers and Dong, ; Byers, ; Balam et al, ) such as temperature (Yamada et al, ; Jyväsjärvi and Kniffki, ; Ahn et al, ), pressure (Mengel et al, ), proprioception (Hassanali, ; Catania and Remple, ; Ozer et al, 2002), osmotic gradients, galvanic potential (Ramirez and Vanegas, ; Heyeraas et al, ), nocioception (Hu et al, ; Lisney, ; Narhi et al, ; Shigenaga et al, 1986; Byers et al, ; Iwata et al, ; Kawarada et al, ; Andrew and Matthews, ), and percussion (Ogawa et al, ; Watanabe et al, ). Sensory nerve fibers and associated nerve bundles are also found in the pulp of other toothed animals (Pischinger and Stockinger, ; Weissengruber et al, ).…”