Abstract
IntroductionThe central nucleus of amygdala plays an important role mediating fear and anxiety responses. It is known that oxytocin microinjections into the central nucleus of amygdala induce hypergrooming, an experimental model of compulsive behavior. We evaluated the behavioral and cardiorespiratory responses of conscious rats microinjected with oxytocin into the central nucleus of amygdala.MethodsMale Wistar rats were implanted with guide cannulae into the central nucleus of amygdala and microinjected with oxytocin (0.5 µg, 1 µg) or saline. After 24 h, rats had a catheter implanted into the femoral artery for pulsatile arterial pressure measurement. The pulsatile arterial pressure was recorded at baseline conditions and data used for cardiovascular variability and baroreflex sensitivity analysis. Respiratory and behavioral parameters were assessed during this data collection session.ResultsMicroinjections of oxytocin (0.5 µg) into the central nucleus of amygdala produced hypergrooming behavior but did not change cardiorespiratory parameters. However, hypergrooming evoked by microinjections of oxytocin (1 µg) into the central nucleus of amygdala was accompanied by increase in arterial pressure, heart rate and ventilation and augmented the power of low and high (respiratory-related) frequency bands of the systolic arterial pressure spectrum. No changes were observed in power of the low and high frequency bands of the pulse interval spectrum. Baroreflex sensitivity was found lower after oxytocin microinjections, demonstrating that the oxytocin-induced pressor response may involve an inhibition of baroreflex pathways and a consequent facilitation of sympathetic outflow to the cardiovascular system.ConclusionsThe microinjection of oxytocin (1 µg) into the central nucleus of amygdala not only induces hypergrooming but also changes cardiorespiratory parameters. Moreover, specific oxytocin receptor antagonism attenuated hypergrooming but did not affect pressor, tachycardic and ventilatory responses to oxytocin, suggesting the involvement of distinct neural pathways.
Highlights
The central nucleus of amygdala plays an important role mediating fear and anxiety responses
A recent study from our laboratory [5] demonstrated that bilateral microinjections of oxytocin (OT) into the central nucleus of amygdala (CeA) of Wistar rats induced hypergrooming, which we proposed as an experimental model of compulsive behavior [5]
Considering that OT has an excitatory role on paraventricular hypothalamic nucleus (PVN) oxytocinergic neurons [6,7], it was suggested that stimulation of PVN OT receptors might induce a release of OT in the CeA and subsequently facilitate the induction of grooming behavior [5]
Summary
The central nucleus of amygdala plays an important role mediating fear and anxiety responses. A recent study from our laboratory [5] demonstrated that bilateral microinjections of oxytocin (OT) into the central nucleus of amygdala (CeA) of Wistar rats induced hypergrooming, which we proposed as an experimental model of compulsive behavior [5]. This behavioral response is dependent on the activation of oxytocinergic afferents from the hypothalamic grooming area, which consists of parts of the paraventricular hypothalamic nucleus (PVN) and dorsal hypothalamic area. Considering that OT has an excitatory role on PVN oxytocinergic neurons [6,7], it was suggested that stimulation of PVN OT receptors might induce a release of OT in the CeA and subsequently facilitate the induction of grooming behavior [5]
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