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The Journal of Neuroscience, September 21, 2005, 25(38):8696-8703; doi:10.1523/JNEUROSCI.1893-05.2005

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Behavioral/Systems/Cognitive
Coding for the Initiation of Pseudopregnancy by Temporally Patterned Activation of Amygdalar NMDA Receptors

Michael L. Lehmann, Heather McKellar, and Mary S. Erskine

Department of Biology, Boston University, Boston, Massachusetts 02215

Female rats modulate the number and interval between the intromissions the female receives during mating. This patterned vaginocervical stimulation (VCS) is critical for triggering long-term changes in prolactin (PRL) secretion necessary for pregnancy or pseudopregnancy (P/PSP). Previous work has shown that NMDA receptor activation in the posterodorsal medial amygdala (MEApd) is required at the time of mating for VCS to induce the twice-daily PRL surges characteristic of P/PSP. The current studies examined whether patterned activation of glutamate receptors within the MEApd induces P/PSP. In anesthetized, cycling females, three 0.27µg NMDA infusions given at 30 min intervals into the MEApd initiated P/PSP, whereas a single NMDA infusion of the same total dose (0.8 µg) had no effect. In conscious, freely behaving females, three infusions of an excitatory amino acid (EAA) mixture applied at the same interval were more effective in initiating P/PSP and nocturnal PRL surges than were single infusions at the same or higher concentrations. Infusion intervals of 5 and 60 min as well as continuous 1 h infusion did not induce P/PSP. Finally, a synergistic effect was observed between EAA and mating stimulation, because a subthreshold EAA infusion combined with subthreshold numbers of intromissions induced P/PSP. These results demonstrate that repeated, properly spaced, temporally discreet periods of glutamate receptor activation within the MEApd, which mimic mating stimulation, encode for P/PSP. Such findings suggest that single intromissions normally release individually subthreshold quanta of glutamate within the MEApd that summate to induce P/PSP.

Key words: glutamate; medial amygdala; vaginocervical stimulation; neuroendocrine memory; sensory transduction; pacing

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Received May 11, 2005; revised August 11, 2005; accepted August 12, 2005.

This article has been cited by other articles:

				L. E. Northrop and M. S. Erskine Selective Oxytocin Receptor Activation in the Ventrolateral Portion of the Ventromedial Hypothalamus Is Required for Mating-Induced Pseudopregnancy in the Female Rat Endocrinology, February 1, 2008; 149(2): 836 - 842. [Abstract] [Full Text] [PDF]

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