Kunihiro Nakai

The Animal Model of Spinal Cord Injury as an Experimental Pain Model

Pain, which remains largely unsolved, is one of the most crucial problems for spinal cord injury patients. Due to sensory problems, as well as motor dysfunctions, spinal cord injury research has proven to be complex and difficult. Furthermore, many types of pain are associated with spinal cord injury, such as neuropathic, visceral, and musculoskeletal pain. Many animal models of spinal cord injury exist to emulate clinical situations, which could help to determine common mechanisms of pathology. However, results can be easily misunderstood and falsely interpreted. Therefore, it is important to fully understand the symptoms of human spinal cord injury, as well as the various spinal cord injury models and the possible pathologies. The present paper summarizes results from animal models of spinal cord injury, as well as the most effective use of these models.

5-HT2C receptor agonists attenuate pain-related behaviour in a rat model of trigeminal neuropathic pain.

Peripheral branches of the trigeminal nerve may be damaged during maxillofacial injury or surgical procedures and trigeminal trauma may induce severe pain that is very challenging to treat. Chronic constriction injury to the infraorbital nerve (ION‐CCI) by loose ligatures has proven a useful model for some types of trigeminal neuropathic pain disorder. Using ION‐CCI rats, we examined the antiallodynic effects of intrathecally administered agents which are selective for 5‐HT2C receptors. Allodynia was evaluated by applying von Frey filaments to skin innervated by the injured ION. Dose‐dependent antiallodynic effects followed administration of three 5‐HT2C receptor agonists, 6‐chloro‐2‐(1‐piperazinyl)‐pyrazine (MK212: 10, 30, and 100 μg); (S)‐2‐(chloro‐5‐fluoro‐indol‐l‐yl)‐1‐methyamine fumarate (RO 60‐0175: 10, 30, and 100 μg); (AaR)‐8,9‐dichloro‐2,3,4,4a‐tetrahydro‐1H‐pyrazino[1,2‐a]quinoxalin‐5(6H)‐one (WAY‐161503: 10, 30, and 100 μg). ED50 values for antiallodynic effects of MK212, RO 60‐0175, and WAY‐161503 were 39.62, 46.67, and 51.22 μg, respectively. Intrathecal administration of the 5‐HT2C receptor antagonist, 8‐[5‐2,4‐dimethoxy‐5‐(4‐trifluoromethylphenylsulphonamido)phenyl‐5‐oxopentyl]‐1,3,8‐triazaspiro[4,5]decane‐2,4‐dione (RS‐102221: 30 μg) did not alter the mechanical threshold. Intrathecal pretreatment with RS‐102221 (10 and 30 μg) reduced the antiallodynic effects of the highest dose of 5‐HT2C agonists. These results indicated that, in this rat model, the 5‐HT2C receptor plays a role in spinal inhibition of trigeminal neuropathic pain.

Functional reconstruction of the upper and lower lips and commissure with a forearm flap combined with a free gracilis muscle transfer.

After resection of an arterio-venous malformation of the upper and lower lips and commissure we performed reconstruction with a forearm flap combined with a free gracilis muscle transfer. First the motor nerve of the gracilis muscle was anastomsed to a buccal nerve branch in the cheek. In a second operation, the red lip was reconstructed with an oral mucosal graft, and the upper lip skin was reconstructed with a local flap. The patient obtained good oral sphincter function for eating, speaking and air inflation.

Serotonin2C receptor mRNA editing in neuropathic pain model.

We investigated the effects on 5HT(serotonin) 2C receptor RNA editing efficiency of contusive SCI (spinal cord injury). Using cloning followed by sequence analysis on spinal cord samples taken, we compared mRNA editing. Our results might be evidence of a functional adaptation mechanism in which increased expression of 5HT2C mRNA isoforms that encode receptors more sensitive to serotonin works to activate brainstem-spinal descending 5HT systems to, in effect, suppress transmission of nociceptive signals from primary afferent neurons to the spinal dorsal horn.

The role of RNA editing of the serotonin 2C receptor in a rat model of oro-facial neuropathic pain

We examined whether infraorbital nerve injury affected the RNA editing efficiency of the serotonin (5HT) 2C receptor in the cervical spinal cord, in association with increased pain thresholds, and whether a 5HT reuptake inhibitor (fluvoxamine; Depromel®, Meiji Seika, Tokyo, Japan) altered this editing. Accordingly, we injured rats with an infraorbital nerve loose ligation and examined the pain thresholds, mRNA and mRNA editing of the 5HT2C receptor. We evaluated changes in mRNA editing and 5HT2C mRNA expression using cloning along with sequence analysis and quantitative reverse transcription‐polymerase chain reaction to compare samples taken at post‐injury day 28 from spinal cord sites, including the trigeminal nucleus caudalis, in naive, sham and injured rats (groups of each type had also received fluvoxamine). 5HT2C receptor expression was maintained post‐injury. The RNA editing efficiency was statistically significantly lower at molecular sites A and B in ipsilateral spinal cord samples from injured rats than in bilateral samples from naive and sham rats, and in contralateral samples from injured rats. After injury, the proportional presence of two receptor isoforms changed, i.e. statistically significantly less VNV and significantly more INV and ISV. The proportions reverted after fluvoxamine administration. The post‐injury change might be evidence of a functional adaptation mechanism that increases the expression of 5HT2C mRNA isoforms that encode receptors that are more sensitive to 5HT. This would activate the brainstem–spinal descending 5HT systems and, in effect, suppress nociceptive signals from primary afferent neurons to the spinal trigeminal nucleus caudalis.

Breast reconstruction using the sensate latissimus dorsi musculocutaneous flap.

&NA; The authors performed immediate breast reconstruction on four patients using a sensate latissimus dorsi musculocutaneous flap accompanied by neurorrhaphy during the past 6 years. In the neurorrhaphy, the lateral cutaneous branch of the dorsal primary divisions of the seventh thoracic nerve, which controls the sensation of the myocutaneous flap, was anastomosed to the lateral cutaneous branch of the fourth intercostal nerve, which controls the sensation of the breast. The subjects consisted of four patients whose postoperative follow‐up period was 14 to 29 months, with an average of 19.3 months. The control subjects consisted of 10 cases with a latissimus dorsi musculocutaneous flap whose sensory nerve had not been reconstructed (postoperative follow‐up period, 15 to 49 months; average, 26.9 months). The sensory examination included tests of touch, pain, and temperature. The innervated musculocutaneous flap sensation showed gradual recovery at about 6 months after surgery and reached the value of the normal side after about 1 year. In the control subjects, the recovery was gradual after more than 1 year and reached the value of the normal side in only some of the control subjects. On the basis of these findings, the authors consider the present technique to be useful for the recovery of sensation in immediate breast reconstruction. (Plast. Reconstr. Surg. 109: 1897, 2002.)

Skin-sparing mastectomy and immediate reconstruction with a deep inferior epigastric perforator flap

BackgroundIt is important for breast reconstruction after mastectomy to recreate immediately good breast symmetry with an adequate amount of soft tissue.MethodsEight patients with breast cancer underwent skin-sparing mastectomy and immediate reconstruction with a deep inferior epigastric perforator flap. This operative technique, and the results, advantages, and disadvantages of the technique were assessed.ResultsSeven patients had stage IIA disease, and one patient had stage I disease. An arc-shaped incision was made just at the lateral border of the breast in all patients. Three patients had a separate periareolar incision, and one had a cicumferential nipple incision. There was 100% flap survival, and good breast symmetry was achieved in all patients. No major perioperative complications occurred in this series. A small amount of fat necrosis occurred in one flap. One patient had slight abdominal bulging. Minor wound-healing problems at the lateral breast skin envelope occurred in two patients.ConclusionThese data indicate that skin-sparing mastectomy and immediate reconstruction with a DIEP flap is a reliable and safe technique. This method is a potentially useful surgical technique, which has achieved very promising results.

Regional differences in ultrasonic assessment of subcutaneous fat thickness in the abdomen: Effects on the TRAM flap

The authors describe the results of fat thickness patterning of the abdominal sites in 50 patients, all of whom required breast reconstruction with a transverse rectus abdominis musculocutaneous flap. The thickness of the abdominal fat was measured at 12 anatomic locations with an ultrasonic instrument. The highest value of the subcutaneous fat thickness was 29.0 ± 10.0 mm at a site 2 cm below the umbilicus at the center of the rectus abdominis muscle. The lowest value of the subcutaneous fat thickness was 17.8 ± 7.6 mm at a site 2 cm above the umbilicus on the anterior superior iliac spine. Average subcutaneous fat thickness over the abdomen of 50 patients was 24.0 ± 9.4 mm. There were 13 patients (group 1) who had an abdominal fat thickness of more than 30 mm, 19 patients (group 2) with an abdominal fat thickness less than 30 mm and more than 20 mm, and 18 patients (group 3) with an abdominal fat thickness less than 20 mm. Complications occurred in 12 of 50 flaps (24%). Among groups 1, 2, and 3 there was no significant difference (p < 0.01) in the overall flap complications (15.4: 36.8: 16.7). In summary, subcutaneous fat thickness showed the higher value at the center of the abdomen and the lower value at the lateral site. Abdominal fat thickness is not a risk factor for necrosis of pedicled transverse rectus abdominis musculocutaneous flaps in patients who are thin, average, or mildly obese. Preoperative examination of the abdominal subcutaneous fat thickness should provide useful information for detailed simulation of a reconstructive operation.

P2X4 receptor expression in a rat model of trigeminal neuropathic pain.

We investigated the P2X4 receptor (P2X4R) expression in the cervical spinal cord, trigeminal ganglion, and infraorbital nerve (ION), after a chronic constriction injury of unilateral ION and a treatment with selective serotonin reuptake inhibitor (SSRI). A recent study has showed that SSRI inhibits P2X4R expression. Injured rats had significantly lower pain thresholds. In injured and slightly injured ION, the P2X4R expression was significantly higher than in the naïve-rat ION. Injured animals with SSRI showed significantly higher pain thresholds than injured animals without the drug. Nonetheless, P2X4R expression in the ipsilateral ION remained high. Immunostaining showed that macrophages are the source of P2X4R. Our results suggest that the expression of P2X4R in our model is modulated not by neuropathic pain, but by slight nerve injury.

Serotonin 2C receptor alternative splicing in a spinal cord injury model

Spinal cord injury can have debilitating consequences, commonly resulting in motor dysfunction below the lesion site and the development of chronic pain syndromes. The serotonin pathway is important for inhibiting noxious stimuli and facilitating motor function after spinal cord injury. The serotonin 2C receptor (5HTR2C) has several characteristic features, and is regulated by the amount of serotonin 2C receptor as well as RNA editing and alternative splicing. In this study, we used a rat model of spinal contusion injury to investigate the relationship between the pain threshold and 5HTR2C alternative splicing. The pain threshold was assessed using mechanical stimulation with von Frey filaments. We then used real-time PCR to examine the RNA levels of 5HTR2C in three sections of the spinal cord: the rostral, injury-core, and caudal positions. On postoperative day 12, the pain threshold in injured rats was significantly reduced compared with sham-operated and naïve rats. The total 5HTR2C levels were significantly lower in injured rats than in naïve rats at all positions, and significantly lower in injured rats compared with sham-operated rats at injury-core and caudal positions. The ratio of exon Vb-skipped nonfunctional 5HTR2C mRNA to total 5HTR2C was significantly higher in injured rats compared with naïve rats at the injury-core and caudal positions, and significantly higher in injured rats compared with sham-operated rats at the caudal position. These results indicate that spinal contusion injury, which causes neuropathic pain, induces serotonergic dysfunction. This dysfunction appears to be mediated by decreased 5HTR2C mRNA expression, and alternative splicing. These results confirm the importance of considering splice variants when examining 5HTR2C.