Both the Suprachiasmatic Nucleus and the Superior Ovarian Nerve Contribute to the Processes of Ovulation and Steroid Hormone Secretion on Proestrus

Abstract

The aims of the present study were to analyze if the superior ovarian nerve (SON) plays a role in the neural signals from suprachiasmatic nucleus (SCN) that lead to ovulation and ovarian steroids secretion on proestrus day. Rats on proestrus day were treated at 11.00 to 11.30 or 17.00 to 17.30 hours with 1 of the 3 experimental procedures (1) unilateral or bilateral SON sectioning, (2) unilateral or bilateral injury to the SCN, or (3) unilateral injury to the SCN followed by unilateral sectioning of the SON ipsilateral to the treated SCN. Treatments were evaluated 24 hours after surgical procedures. Compared to laparotomized animals, right or bilateral SON sectioning treatment at 17.00 hours resulted in lower ovulation rates and number of ova shed by the right ovary. The ovaries of nonovulating animals showed early follicular luteinization signs and trapped ova. Bilateral SCN injury treatment at 11.00 hours resulted in anovulation; whereas right SCN injury treatment, with or without right SON sectioning, resulted in a lower number of ova shed. Injecting luteinizing hormone-releasing hormone to animals with bilateral SCN injury restored ovulation. In rats with unilateral or bilateral SON sectioning, or with injury to the SCN with or without unilateral sectioning of the SON, the effects on hormone levels depended of the hormone studied and the time of day treatment was performed. The present results suggest that on proestrus day, the role of the right or both SON in ovulation and steroid hormone secretion regulation takes place through different neuroendocrine mechanisms from SCN.

Stimulation of nicotinic receptors in the suprachiasmatic nucleus results in a higher number of growing follicles and ova shed

“…Ramírez et al. () showed that neural information arising from the right SCN and into the ovaries via the superior ovarian nerve (SON) played a stimulatory role in follicle reactivity to LH that results in ovulation, while the neural information arising from the left SCN did not appear essential for this process.…”

“…Previously, we showed that neural information arising from the SCN and traveling to the ovary via the SON played a physiological role in the circadian regulation of ovulation (Ramírez et al., ). In the present study, nicotine‐treated rats showed a higher number of growing small follicles, suggesting that a neuronal signal that originates in the SCN and travels through the SON and/or the vagus nerve is related to the neuroendocrine regulation of the stimulation of follicular maturation.…”

The Neural Signals of the Superior Ovarian Nerve Modulate in an Asymmetric Way the Ovarian Steroidogenic Response to the Vasoactive Intestinal Peptide

“…The sham surgery procedure was performed following a previously described methodology ( Morales-Ledesma et al, 2011 , 2012 ; Ramírez et al, 2017 ). In brief, a dorso-lateral incision on the left or right side of the abdominal wall (L-Sham or R-Sham) was performed 2 cm below the last rib.…”

“…The section of the left or right SON (L-SON or R-SON, respectively) was performed according to previously described methodology ( Morales-Ledesma et al, 2010 , 2012 ; Ramírez et al, 2017 ). In brief, the anesthetized animals were submitted to a dorso-lateral incision as described above.…”

“…Previously, we showed that in the prepubertal rat, the effects of unilateral section of the SON on steroid hormone levels were asymmetric and depend on the hormone analyzed and the elapsed time between surgery and autopsy ( Morales-Ledesma et al, 2012 ). In the adult rat, the SON modulates steroid hormones secretion in an asymmetric way, depending on the hour of day ( Ramírez et al, 2017 ) and the day of the estrous cycle ( Flores et al, 2011 ).…”