Contextual cues and vaginocervical stimuli are integrated in the medial amygdala during mating in female syrian hamsters

Deborah Nell Shelley, Purdue University

Abstract

In rodents, though ovulation is spontaneous, vaginocervical stimulation (VCS) is required for the induction of the neuroendocrine reflex (NER) that supports pregnancy, or in the case of sterile mating, pseudopregnancy. Rodents have species-specific mating stimulation requirements for NER induction. Additionally, the female receives male distal stimulation during mating (i.e. auditory, olfactory, visual), which can modulate the effects of VCS during mating processes by providing contextual cues. The overarching goal of the research was the investigation of the functional relationship between behavioral stimuli received during mating by the female Syrian hamster and subsequent physiological responses. An unexplored feature of this relationship has been the effect of male contextual cues on NER induction. To investigate the possibility that peripheral mechanisms affect rodent species differences in NER stimulation requirements, a neuronal tracing technique that resulted in discrete cervical tracer injection sites established the afferent connections of the hamster cervix to the spinal cord. Results showed that the hamster cervix afferents project solely to the lumbosacral spinal cord, whereas reportedly, rat afferents project to both the lumbosacral and the thoracolumbar spinal cord. Pseudopregnancy induction tests measured the impact of mating stimuli, particularly contextual cues, on NER induction. With our manual VCS technique, contextual cues at the time of stimulation were necessary for NER induction. c-Fos immunohistochemistry identified brain regions that were sensitive to the components of mating stimulation. Ventromedial hypothalamus neurons were activated by male-related contextual cues, while both male-related contextual cues and VCS activated medial amygdala neurons. To investigate the interplay of brain networks involved in reproductive processes, females with medial amygdala lesions were tested sequentially for ovarian cyclicity, mating behavior, pseudopregnancy induction, and the rewarding consequences of mating. It was shown that the medial amygdala is critical to pseudopregnancy induction, but no other process tested. In conclusion, (1) neuroanatomical differences may affect rodent species-specific NER stimulation requirements, (2) contextual cues provided by the male hamster during mating have an impact on NER induction, and (3) the medial amygdala, which is critical for NER induction, integrates contextual cues and VCS during mating.

Degree

Ph.D.

Advisors

Meisel, Purdue University.

Subject Area

Neurology|Anatomy & physiology|Animals

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