The effect of multiple electrical stimulation in the medial preoptic area and the medial amygdala on maternal behavior in the female rat

A set of experiments was conducted to investigate the functions of the medial preoptic area (MPOA) and the medial amygdala (MedAmyg) and their relationship with regards to maternal (and related) behavior(s) using electrical (kindling-like) stimulation. This procedure is thought to enhance the function of the substrate being stimulated and has never been used before to investigate maternal behavior. A program of repeated electrical stimulation was applied daily for 14 days using 2 second trains of biphasic square wave pulses at 60 Hz, 1 ms duration and 300--500muA. Confirmation of after discharge (AD) using these parameters was established. Electrophysiological data showed strong transfer of AD from the MedAmyg to the MPOA, but not in the other direction (suggesting unidirectional circuitry). In the first experiment, maternally experienced (but not post-partum) MedAmyg stimulated animals became maternal more slowly than did MedAmyg not stimulated animals or than MPOA stimulated animals. In the second experiment, virgin animals were used. MPOA stimulation enhanced the female's preference for pup associated environments in the conditioned place preference (CPP) paradigm. MedAmyg stimulation had no effect on CPP performance, but produced a decreased preference for pup odors in a modified hole board test and increased 'anxiety' in the open field. The third experiment investigated the interaction of electrical stimulation and pup exposure in virgin females. MPOA stimulation interacted with pup exposure to further reduce the latency to become maternal. Finally, the forth study investigated the effects of MPOA/MedAmyg stimulation in stria terminalis lesioned maternally experienced females. Results were consistent with above studies, except MedAmyg stimulation only partially attenuated maternal behavior in the lesion condition. Generally, these results confirm that the MPOA and the MedAmyg are involved in facilitating and attenuating maternal responsiveness and related (precursor?) behaviors, respectively. It appears that chronic (kindling-like) stimulation of these neural substrates enhances their functions. MPOA stimulated facilitation is further enhanced by pup experience. Also, the attenuation of maternal behavior appears to be (at least somewhat) dependent on the MedAmyg connections with the MPOA. This set of experiments clarifies our understanding of MPOA/MedAmyg functioning and their relationship with regards to maternal behavior. The technique used in this experiment is a useful tool for investigating the function of neural substrates.