Morphometric comparison between phrenic nerve fascicles of male and female spontaneously hypertensive rats (SHR).
MORPHOMETRIC COMPARISON BETWEEN PHRENIC NERVE FASCICLES OF MALE AND FEMALE SPONTANEOUSLY HYPERTENSIVE RATS (SHR). Anaceres Rodrigues Ribeiro, Helio Cesar Salgado, Valeria Paula Sassoli Fazan; School of Medicine of Ribeirao Preto--University of Sao Paulo, Brasil.
The phrenic nerve is the main nerve involved in respiration. Nevertheless, besides the motor fiber to the diaphragm, the phrenic nerve contains sympathetic fibers that present rhythmical discharges synchronic to respiration, which are variable among different animal species. It is well known that spontaneously hypertensive rats (SHR) show sympathetic hyperactivity. This hyperactivity has been related to the hypertension development in these animals. Despite this, the morphology and morphometry of the phrenic nerve in this animal strain has never been investigated. Moreover, there are important differences in arterial pressure (AP) levels and heart rate (HR) between male and female SHR, indicating the need of a comparison between genders. In this way, the aims of the present study were to perform a descriptive, qualitative and quantitative light microscopy study of the phrenic nerve in SHR, comparing proximal and distal segments on the same side, and same levels on different sides and between gender. After the AP and HR recordings, phrenic nerves of young adult (20 week-old) male (N = 9) and female SHR (N = 10) were prepared for epoxy resin embedding and light microscopy study. Morphometric analysis was performed with the aid of a computer software (KS 400, v. 2.0). Statistical analysis was appropriately performed and differences were considered significant when p < 0.05. Our results showed an important longitudinal asymmetry (proximal vs distal segments) on both sides, for male and female SHR. Also, there was an asymmetry between sides on distal segments. Phrenic nerves were generally larger in males compared to females. Nevertheless, myelinated fiber number and density were significantly larger on females. These results suggest that the nerve size is related to the animal size, since males were larger and heavier than females. However, differences on fiber number are being described for the first time in this animal strain, suggesting the need for detailed functional studies on phrenic nerves of male and female SHR. This investigation might contribute to a better understanding of the gender differences in arterial pressure of SHR.
Support: FAPESP 02/09406-5, 04/01390-8, 04/09139-2, 06/03200-7, CNPq 501230/2003-8, CAPES and FAEPA
Key Words: Phrenic nerve; Spontaneously hypertensive rats; Gender differences; Morphometry.