The bradycardic and hypotensive responses to serotonin are reduced by activation of GABAA receptors in the nucleus tractus solitarius of awake rats

Cardiovascular Autonomic Responses in the VCD Rat Model of Menopause: Effects of Short- and Long-Term Ovarian Failure

After menopause, hypertension elevates the risk of cardiac diseases, one of the major causes of women's morbidity. The gradual depletion of ovarian follicles in rats, induced by 4-vinylcyclohexene diepoxide (VCD), is a model for studying the physiology of menopause. 4-Vinylcyclohexene diepoxide treatment leads to early ovarian failure (OF) and a hormonal profile comparable to menopause in humans. We have hypothesized that OF can compromise the balance between sympathetic and parasympathetic tones of the cardiovascular system, shifting toward dominance of the former. We aimed to study the autonomic modulation of heart and blood vessels and the cardiovascular reflexes in rats presenting short-term (80 days) or long-term (180 days) OF induced by VCD. Twenty-eight-day-old Wistar rats were submitted to VCD treatment (160 mg/kg, intraperitoneally) or vehicle (control) for 15 consecutive days and experiments were conducted at 80 or 180 days after the onset of treatment. Long-term OF led to an increase in the sympathetic activity to blood vessels and an impairment in the baroreflex control of the heart, evoked by physiological changes in arterial pressure. Despite that, long-term OF did not cause hypertension during the 180 days of exposure. Short-term OF did not cause any deleterious effect on the cardiovascular parameters analyzed. These data indicate that long-term OF does not disrupt the maintenance of arterial pressure homeostasis in rats but worsens the autonomic cardiovascular control. In turn, this can lead to cardiovascular complications, especially when associated with the aging process seen during human menopause.

Serotonin and blood pressure regulation

5-Hydroxytryptamine (5-HT; serotonin) was discovered more than 60 years ago as a substance isolated from blood. The neural effects of 5-HT have been well investigated and understood, thanks in part to the pharmacological tools available to dissect the serotonergic system and the development of the frequently prescribed selective serotonin-reuptake inhibitors. By contrast, our understanding of the role of 5-HT in the control and modification of blood pressure pales in comparison. Here we focus on the role of 5-HT in systemic blood pressure control. This review provides an in-depth study of the function and pharmacology of 5-HT in those tissues that can modify blood pressure (blood, vasculature, heart, adrenal gland, kidney, brain), with a focus on the autonomic nervous system that includes mechanisms of action and pharmacology of 5-HT within each system. We compare the change in blood pressure produced in different species by short- and long-term administration of 5-HT or selective serotonin receptor agonists. To further our understanding of the mechanisms through which 5-HT modifies blood pressure, we also describe the blood pressure effects of commonly used drugs that modify the actions of 5-HT. The pharmacology and physiological actions of 5-HT in modifying blood pressure are important, given its involvement in circulatory shock, orthostatic hypotension, serotonin syndrome and hypertension.

Neuroanatomic relationships between the GABAergic and serotonergic systems in the developing human medulla

gamma-Amino butyric (GABA) critically influences serotonergic (5-HT) neurons in the raphé and extra-raphé of the medulla oblongata. In this study we hypothesize that there are marked changes in the developmental profile of markers of the human medullary GABAergic system relative to the 5-HT system in early life. We used single- and double-label immunocytochemistry and tissue receptor autoradiography in 15 human medullae from fetal and infant cases ranging from 15 gestational weeks to 10 postnatal months, and compared our findings with an extensive 5-HT-related database in our laboratory. In the raphé obscurus, we identified two subsets of GABAergic neurons using glutamic acid decarboxylase (GAD65/67) immunostaining: one comprised of small, round neurons; the other, medium, spindle-shaped neurons. In three term medullae cases, positive immunofluorescent neurons for both tryptophan hydroxylase and GAD65/67 were counted within the raphé obscurus. This revealed that approximately 6% of the total neurons counted in this nucleus expressed both GAD65/67 and TPOH suggesting co-production of GABA by a subset of 5-HT neurons. The distribution of GABA(A) binding was ubiquitous across medullary nuclei, with highest binding in the raphé obscurus. GABA(A) receptor subtypes alpha1 and alpha3 were expressed by 5-HT neurons, indicating the site of interaction of GABA with 5-HT neurons. These receptor subtypes and KCC2, a major chloride transporter, were differentially expressed across early development, from midgestation (20 weeks) and thereafter. The developmental profile of GABAergic markers changed dramatically relative to the 5-HT markers. These data provide baseline information for medullary studies of human pediatric disorders, such as sudden infant death syndrome.