Study of the mechanisms by which VCS induces the 10-13 days of twice-daily PRL surges, while at present incompletely understood, will help us to answer several more general neural and endocrine questions: 1) what similarities exist between the suckling-induced and VCS-induced changes in pituitary hormone release, and what central and peripheral mechanisms might be common to both; 2) how do sensory and behavioral factors initiate changes in the pattern of hormone secretion; and 3) what are the mechanisms underlying the establishment of the short-term and long-term mnemonic devices, and do alterations in neural function similar to those responsible for other types of memory underlie this memory? As the data summarized above demonstrate, a neuroethological approach to the study of these questions can be very valuable. The reasons for this are severalfold. First, using naturally occurring behavior as an inducer of PSP, it is possible to use appropriate controls that allow identification of proximal responses that are directly linked to VCS. Females exposed to intromissive stimuli from males show responses that are not shown by females receiving the same flank and perineal somatosensory input from mounts-without-intromission or the olfactory input from nonmating exposure to males. Artificial VCS may induce some nonspecific responses that may be more perceived than real. Second, VCS received by the female during mating is very different from that applied by mechanical or electrical means, and it has been shown that the natural stimuli are important for induction of the PRL surges. The fact that intromissions are normally repeated and intermittent has revealed that the female responds initially with a graded response to these stimuli and that there is a threshold that has to be met for the full response to occur. The set-point of this threshold is influenced by factors that are as yet unknown. Finally, the natural mating condition reveals the contributions of the short-term and long-term mnemonic devices, establishing the existence of a graded to all-or-nothing transition that is required for the occurrence of PSP. In each of these cases, it is clear that these phenomena are obscured when supramaximal artificial stimulation is used as a method to induce PSP. Use of behaviorally appropriate stimulation will continue to be a productive way to study this system.(ABSTRACT TRUNCATED AT 400 WORDS).