Substance P in Dorsal Root Ganglion Neurons in Young and Adult Rats, after Nociceptive Stimulation during the Neonatal Period.

The nervous system is highly plastic during the neonatal period, being sensitive to noxious stimuli, which may cause short- and long-term pain responsivity changes. Understanding plasticity in peripheral pain pathways is crucial, particularly when the nervous system is still under development and remodeling process. Substance P (SP) is widely used as a marker for peripheral neurons with unmyelinated and small myelinated fibers. We investigated the number of SP immunoreactive neurons in the dorsal root ganglion (DRG) of male and female Wistar rats, 15 and 180 days after nociceptive stimulation during the neonatal period. Right and left 5th lumbar (L5) DRG were incubated in rabbit polyclonal anti-substance P primary followed by biotinylated donkey anti-rabbit secondary antibodies. Reaction was revealed with a nickel-diaminobenzidine solution. Labeled neurons were counted and compared between ages, genders and groups. Gender differences were present in both ages, with the number of SP-positive DRG neurons being larger in 15-days-old males on both sides. After 180 days, males showed a larger number of SP-positive neurons than females only on the nociceptive stimulated side. An increased number of SP-positive neurons in the DRG on the stimulated side was present in females, immediately after nociceptive stimulation, but not after 180 days. In conclusion, neonatal noxious stimulation caused a permanent increase in SP-positive DRG neurons in males that was not observed in females, suggesting that differences in pain processing/responsivity between genders could be related to morphological alterations of the nervous system. Anat Rec, 301:849-861, 2018. © 2017 Wiley Periodicals, Inc.

Recurrent laryngeal nerve alterations in developing spontaneously hypertensive rats.

OBJECTIVES/HYPOTHESIS: It is well known that the recurrent laryngeal nerve not only innervates the larynx but also contains baroreceptor fibers, as demonstrated by physiological studies. Because hypertension has a negative impact on both peripheral nerve morphology and the baroreflex, we investigated the recurrent laryngeal nerve morphological alterations related to the development of hypertension. METHODS: We compared morphological and morphometric aspects of different segments of the recurrent laryngeal nerve in male and female spontaneously hypertensive rats in different ages: 5, 8, and 20 weeks (n = 6 per group). Blood pressure and heart rate were recorded in anesthetized animals, followed by removal of the right and left recurrent laryngeal nerves for epoxy resin embedding and light microscopy analysis. Computer software was used for morphometric analysis. RESULTS: The blood pressure was significantly higher in 20-week-old animals compared to those at 5 weeks. Body weight increased significantly with age, as did the nerve fascicles. For the myelinated fibers and respective axons, there was a reduction of fiber size, more evident on the axon, associated with a reduction of the small myelinated fibers percentage in animals with high blood pressure. Also, 20-week-old animals showed a significant reduction of the blood vessel percentage of occupancy compared to younger ages. No differences were observed between genders. CONCLUSION: Hypertension development impaired axon growth, affecting mainly the small myelinated fibers. Males and females were affected equally. The alterations of the endoneural blood vessels probably played an important role on the small fibers alterations.