Activation of prefrontal cortical parvalbumin interneurons facilitates extinction of reward-seeking behavior.

Forming and breaking associations between emotionally salient environmental stimuli and rewarding or aversive outcomes is an essential component of learned adaptive behavior. Importantly, when cue-reward contingencies degrade, animals must exhibit behavioral flexibility to extinguish prior learned associations. Understanding the specific neural circuit mechanisms that operate during the formation and extinction of conditioned behaviors is critical because dysregulation of these neural processes is hypothesized to underlie many of the maladaptive and pathological behaviors observed in various neuropsychiatric disorders in humans.

Integrating optogenetic and pharmacological approaches to study neural circuit function: current applications and future directions.

Optogenetic strategies to control genetically distinct populations of neurons with light have been rapidly evolving and widely adopted by the neuroscience community as one of the most important tool sets to study neural circuit function. Although optogenetics have already reshaped neuroscience by allowing for more precise control of circuit function compared with traditional techniques, current limitations of these approaches should be considered. Here, we discuss several strategies that combine optogenetic and contemporary pharmacological techniques to further increase the specificity of neural circuit manipulation.

Photoperiod and reproductive condition are associated with changes in RFamide-related peptide (RFRP) expression in Syrian hamsters (Mesocricetus auratus).

To conserve scarce energetic resources during winter, seasonal breeders inhibit reproduction and other nonessential behavioral and physiological processes. Reproductive cessation is initiated in response to declining day lengths, a stimulus represented centrally as a long-duration melatonin signal. The melatonin signal is not decoded by the reproductive axis directly, but by an unidentified neurochemical system upstream of gonadotropin-releasing hormone (GnRH).

Suppression of kisspeptin expression and gonadotropic axis sensitivity following exposure to inhibitory day lengths in female Siberian hamsters.

To avoid breeding during unsuitable environmental or physiological circumstances, the reproductive axis adjusts its output in response to fluctuating internal and external conditions. The ability of the reproductive system to alter its activity appropriately in response to these cues has been well established. However, the means by which reproductively relevant cues are interpreted, integrated and relayed to the reproductive axis remain less well specified.

Environmental control of kisspeptin: implications for seasonal reproduction.

The KiSS-1 gene encodes the peptide hormone kisspeptin, which acts as a principal positive regulator of the reproductive axis by directly stimulating GnRH neuron activity. To gain insight into a potential role for kisspeptin in integrating and relaying reproductively relevant stimuli to the GnRH system, we investigated changes in kisspeptin peptide expression associated with photoperiodic changes in reproductive state as well as pituitary and gonadal responses to peripheral kisspeptin injections. Seasonally breeding rodents undergo pronounced fluctuations in reproductive state in response to changing day lengths.

Identification and characterization of a gonadotropin-inhibitory system in the brains of mammals.

Successful reproduction requires maintenance of the reproductive axis within fine operating limits through negative feedback actions of sex steroids. Despite the importance of this homeostatic process, our understanding of the neural loci, pathways, and neurochemicals responsible remain incomplete. Here, we reveal a neuropeptidergic pathway that directly links gonadal steroid actions to regulation of the reproductive system.