Coding for the Initiation of Pseudopregnancy by Temporally Patterned Activation of Amygdalar NMDA Receptors

Abstract

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 0.27 g 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 g) 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.

Urine Scent Marking (USM): A Novel Test for Depressive-Like Behavior and a Predictor of Stress Resiliency in Mice

“…Female mice were maintained in a separate room, and the estrous stage was determined by visual inspection as previously described [36], [37] and confirmed by evaluating vaginal cytology [38], [39]. Experimental procedures used for collecting female urine and for blotting were adopted from previous reports [40]–[42].…”

Morphological and Functional Features of the Sex Steroid-Responsive Posterodorsal Medial Amygdala of Adult Rats

“…Moreover, our first experimental approach has been applied to test the behavior of adult males to avoid confounding variations due to cyclical changes in circulating sex hormones [40,65,133]. However, this approach does not preclude the role of the MePD in females [32,33,40,134,135].…”

Glial and axonal perikaryal coverage and somatic spines in the posterodorsal medial amygdala of male and cycling female rats

“…In addition, it is noteworthy that sex steroids can remarkably alter the function of the MePD cells by concomitantly affect the number of dendritic spines (for review see Rasia‐Filho et al, ) and the synaptic inputs in both dendritic shafts and spines of cycling female rats (Brusco et al, ). That provides the female MePD with a changeable somatic and dendritic processing of the incoming synaptic activity and a local switch in the neurotransmission depending on the levels of the ovarian hormones (Micevych et al, ; Oro et al, ; Polston and Erskine, ; Lehmann and Erskine, ; Lehmann et al, ; de Castilhos et al, ). We hypothesize that the morphological and synaptic rearrangement in the left MePD can change the inhibitory impact of output projections on hypothalamic circuits during the proestrus phase to disinhibit the activity both in the VMH, involved in lordosis behavior, and in the MPOA, for the display of proreceptive behavior (Pfaus and Heeb, ; for additional data and comments see Rasia‐Filho et al, ; Brusco et al, ).…”