Male rats received normal chow or high-fat diets rich in dextrose (HFD) or sucrose (HFS). Half of the rats received 90-day unrestricted access to their diet prior to training, whereas the other half were food restricted throughout the study. We evaluated the effects of these dietary manipulations on discrimination and reversal performance and on post-training levels of brain-derived neurotrophic factor (BDNF) in the prefrontal cortex and the ventral and dorsal hippocampus. Neither diet nor restriction condition affected discrimination acquisition. However, prior unrestricted access to the HFD diet impaired discrimination reversal learning and reduced BDNF in the prefrontal cortex and ventral hippocampus. Also, rats given the HFD diet responded more than controls to the previously rewarded cue at the outset of discrimination reversal. The results suggest that consumption of the HFD diet may have had enduring effects on learning processes, some of which may contribute to the control of intake regulation.

The neurobiology of female sexual behavior has largely focused on mechanisms of hormone action on nerve cells and how these effects translate into the display of copulatory motor patterns. Of equal importance, though less studied, are some of the consequences of engaging in sexual behavior, including the rewarding properties of sexual interactions and how sexual experience alters copulatory efficiency. This review summarizes the effects of sexual experience on reward processes and copulation in female Syrian hamsters. Neural correlates of these sexual interactions include longterm cellular changes in dopamine transmission and postsynaptic signaling pathways related to neuronal plasticity (e.g., dendritic spine formation). Taken together, these studies suggest that sexual experience enhances the reinforcing properties of sexual behavior, which has the coincident outcome of increasing copulatory efficiency in a way that can increase reproductive success.

Drugs of abuse produce long-term changes in dopamine neurotransmission and receptor-effected intracellular signaling. Similar changes in neuronal activity are mediated by motivated behaviors. To explore cellular mechanisms underlying these neuroadaptations following sexual experience, cyclic AMP accumulation following stimulation of D1 dopamine receptors, G-proteins, and adenylate cyclase was compared in the nucleus accumbens and caudate nucleus of sexually naive and experienced female hamsters following sexual behavior. Direct stimulation of adenylate cyclase with forskolin or indirectly by activation of G-proteins with Gpp(NH)p produced dose-dependent increases in the formation of cyclic AMP in the nucleus accumbens and caudate nucleus, with no effects of sexual experience on these measures. Specific D1 receptor stimulation increased Gpp(NH)p-induced adenylate cyclase activity in the nucleus accumbens and caudate nucleus of all animals. Interestingly, this stimulation was further enhanced only in membranes from the nucleus accumbens, but not from the caudate nucleus, of sexually experienced hamsters compared to the response of naive females. These results demonstrate that sexual behavior experience can sensitize mesolimbic dopamine pathways and that this sensitization occurs through an increase in D1 receptor-mediated signaling.

These results show that repeated activation of D2-like receptors in vivo can produce changes in feeding behavior and sensory processing that is associated with sensitization of D1 dopamine receptor-mediated signaling in the caudate-putamen.