The Relationship Between Plasma Oxytocin and Executive Functioning in Huntington's Disease: A Pilot Study

Oxytocin in Huntington’s disease and the spectrum of amyotrophic lateral sclerosis-frontotemporal dementia

Neurodegenerative disorders (NDDs) such as Huntington’s disease (HD) and the spectrum of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterized by progressive loss of selectively vulnerable populations of neurons. Although often associated with motor impairments, these NDDs share several commonalities in early symptoms and signs that extend beyond motor dysfunction. These include impairments in social cognition and psychiatric symptoms. Oxytocin (OXT) is a neuropeptide known to play a pivotal role in the regulation of social cognition as well as in emotional behaviors such as anxiety and depression. Here, we present an overview of key results implicating OXT in the pathology of HD, ALS and FTD and seek to identify commonalities across these NDDs. OXT is produced in the hypothalamus, a region in the brain that during the past decade has been shown to be affected in HD, ALS, and FTD. Several studies using human post-mortem neuropathological analyses, measurements of cerebrospinal fluid, experimental treatments with OXT as well as genetic animal models have collectively implicated an important role of central OXT in the development of altered social cognition and psychiatric features across these diseases. Understanding central OXT signaling may unveil the underlying mechanisms of early signs of the social cognitive impairment and the psychiatric features in NDDs. It is therefore possible that OXT might have potential therapeutic value for early disease intervention and better symptomatic treatment in NDDs.

Oxytocin-Cholinergic Central Interaction: Implications for Non-Social Memory Formation

Oxytocin (OT) and vasopressin (AVP) are two closely related neuropeptides implicated in learning and memory processes, anxiety, nociception, addiction, feeding behavior and social information processing. Regarding learning and memory, OT has induced long-lasting impairment in different behaviors, while the opposite was observed with AVP. We have previously evaluated the effect of peripheral administration of OT or its antagonist (AOT) on the inhibitory avoidance response of mice and on the modulation of cholinergic mechanisms. Here, we replicate and validate those results, but this time through central administration of neuropeptides, considering their poor passage through the blood-brain barrier (BBB). When we delivered OT (0.10 ng/mouse) and its antagonist (0.10 ng/mouse) through intracerebroventricular (ICV) injections, the neuropeptide impaired and AOT enhanced the behavioral performance on an inhibitory avoidance response evaluated 48 h after training in a dose-dependent manner. On top of that, we investigated a possible central interaction between OT and the cholinergic system. Administration of anticholinesterases inhibitors with access to the central nervous system (CNS), the activation of muscarinic acetylcholine (Ach) receptors and the increase of evoked ACh release using linopirdine (Lino) (3-10 µg/kg, IP), reversed the impairment of retention performance induced by OT. Besides, either muscarinic or nicotinic antagonists with unrestricted access to the CNS reduced the magnitude of the performance-facilitating effect of AOT's central infusion. We suggest that OT might induce a cholinergic hypofunction state, resulting in an impairment of IA memory formation, a process for which the cholinergic system is crucially necessary.

Neural Functions of Hypothalamic Oxytocin and its Regulation

Oxytocin (OT), a nonapeptide, has a variety of functions. Despite extensive studies on OT over past decades, our understanding of its neural functions and their regulation remains incomplete. OT is mainly produced in OT neurons in the supraoptic nucleus (SON), paraventricular nucleus (PVN) and accessory nuclei between the SON and PVN. OT exerts neuromodulatory effects in the brain and spinal cord. While magnocellular OT neurons in the SON and PVN mainly innervate the pituitary and forebrain regions, and parvocellular OT neurons in the PVN innervate brainstem and spinal cord, the two sets of OT neurons have close interactions histologically and functionally. OT expression occurs at early life to promote mental and physical development, while its subsequent decrease in expression in later life stage accompanies aging and diseases. Adaptive changes in this OT system, however, take place under different conditions and upon the maturation of OT release machinery. OT can modulate social recognition and behaviors, learning and memory, emotion, reward, and other higher brain functions. OT also regulates eating and drinking, sleep and wakefulness, nociception and analgesia, sexual behavior, parturition, lactation and other instinctive behaviors. OT regulates the autonomic nervous system, and somatic and specialized senses. Notably, OT can have different modulatory effects on the same function under different conditions. Such divergence may derive from different neural connections, OT receptor gene dimorphism and methylation, and complex interactions with other hormones. In this review, brain functions of OT and their underlying neural mechanisms as well as the perspectives of their clinical usage are presented.