The role of hypocretin neurons in modulating somatic motoneuron excitability and hence muscle tone is poorly understood. We investigated whether hypocretin neurons influence the hypoglossal and trigeminal motor pools that innervate the genioglossus and masseter muscles respectively, both of which function to maintain upper airway patency. We hypothesized hypocretin neurons facilitate motor outflow at the motor pools. We pharmacologically manipulated hypocretin neuron activity in anaesthetized mice to determine their role in somatic motoneuron excitability. We also antagonized hypocretin receptors in the hypoglossal motor pool to determine the pathway through which hypocretin neurons influence motoneuron excitability. We demonstrated that hypocretin neurons potently excite somatic motoneurons and hence facilitate genioglossus and masseter muscle tone. Furthermore, we demonstrated that an endogenous hypocretinergic drive on somatic motoneurons facilitated muscle tone under anaesthesia. These studies demonstrate that hypocretin is an excitatory neuromodulator of muscle tone and contributes to the excitatory regulation of somatic motoneurons.

The role of hypocretin neurons in modulating somatic motoneuron excitability and hence muscle tone is poorly understood. We investigated whether hypocretin neurons influence the hypoglossal and trigeminal motor pools that innervate the genioglossus and masseter muscles respectively, both of which function to maintain upper airway patency. We hypothesized hypocretin neurons facilitate motor outflow at the motor pools. We pharmacologically manipulated hypocretin neuron activity in anaesthetized mice to determine their role in somatic motoneuron excitability. We also antagonized hypocretin receptors in the hypoglossal motor pool to determine the pathway through which hypocretin neurons influence motoneuron excitability. We demonstrated that hypocretin neurons potently excite somatic motoneurons and hence facilitate genioglossus and masseter muscle tone. Furthermore, we demonstrated that an endogenous hypocretinergic drive on somatic motoneurons facilitated muscle tone under anaesthesia. These studies demonstrate that hypocretin is an excitatory neuromodulator of muscle tone and contributes to the excitatory regulation of somatic motoneurons.

Orexin A (or hypocretin 1)-immunoreactive neurons in the rat lateral hypothalamus project to several areas of the medulla oblongata that are closely associated with cardiovascular regulation. The present study was undertaken to further strengthen the hypothesis that orexin A accelerates cardiovascular response by activating sympathoexcitatory neurons in the rat rostral ventrolateral medulla (RVLM). First, immunohistochemical studies revealed the presence of orexin A-immunoreactive fibers in the RVLM. Double labeling the sections with orexin A- and tyrosine hydroxylase (TH)-antisera further showed that orexin A-immunoreactive fibers are in close proximity with TH-immunoreactive neurons, some of which may be barosensitive, bulbospinal neurons in the RVLM. Second, microinjection of orexin A (6.35, 12.7 and 38.1 μM) into the RVLM, which was verified later by histological examination, caused a significant increase of mean arterial pressure (MAP) and a moderate increase of heart rate (HR) in awake rats. L-glutamate (33.3 mM) injected into the same sites, caused a larger increase in MAP, but a decrease in HR; whereas, saline injection was without significant effect. Results from this study suggest that orexin A, which may be released from the nerve fibers originating from the neurons in the lateral hypothalamus, acting on RVLM neurons in the medulla, increases sympathetic outflow targeted to the heart and blood vessels in awake animals.

Introduction: In 2021, 2.5 million people aged 12 and older abused the addictive psychostimulant methamphetamine (MA) in the US. MA produces short-lasting euphoria, but also anxiety, erratic behavior, mood disturbance, and abnormal wakefulness. Chronic use of MA can lead to disordered sleep, particularly during withdrawal, and clinical studies have shown that sleep dysfunction is a strong predictor for drug-taking relapse. The neuropeptide hypocretin (HCRT) plays a critical role in the transition to a waking state and also modulates drug reward. Enhanced HCRT signaling in the brain underlies the sleep disorder insomnia and the HCRT-receptor antagonist lemborexant has recently been FDA-approved for treatment of insomnia in humans. Thus, in the current study we characterize sleep dysfunction associated with MA vapor withdrawal and hypothesize that HCRT signaling contributes to negative sleep outcomes. Methods: Adult male Wistar rats (N =8) were implanted with a telemetry device and electroencephalographic/electromyographic signals were recorded for 24 hours (12:12 hours, light:dark cycle). Data were analyzed prior to MA vapor exposure (baseline), and during withdrawal (after one week of MA vapor abstinence). Rats were administered lemborexant (0, and 30 mg/kg, in a counter-balanced order) during withdrawal at the beginning of the light cycle. Results: Rats showed a decrease in time spent in rapid eye movement (REM) sleep in the light cycle during withdrawal, and there was a trend for an increase in time spent in REM sleep during the dark cycle, indicating possible REM sleep rebound. There were no changes to non-REM (NREM) sleep or waking in either the light or dark cycle. The number of bouts of REM sleep decreased during the light cycle, and there was no change in average bout duration in REM sleep during withdrawal compared to baseline. The number of bouts of NREM sleep and waking increased during the dark cycle, while the average bout duration decreased during withdrawal compared to baseline, indicating periods of sleep/wake were more fragmented during the dark cycle. In addition, administration of lemborexant restored the amount of time spent in REM sleep and the number of REM sleep bouts during the light cycle. Conclusions: Overall, these findings show there is a role for HCRT neurotransmission in the observed dysregulated and fragmented sleep of male rats during MA withdrawal. Future research should look at gender differences for sleep dysfunction and MA withdrawal, as well as long-term consequences of MA use.

No description available.

Hypocretin/Orexin (HCRT) is a neuropeptide that is associated with both stress and reward systems in humans and rodents. The different contributions of signaling at hypocretin-receptor 1 (HCRT-R1) and hypocretin-receptor 2 (HCRT-R2) to compulsive alcohol drinking are not yet fully understood. Thus, the current studies used pharmacological and viral-mediated targeting of HCRT to determine participation in compulsive alcohol drinking and measured HCRT-receptor mRNA expression in the extended amygdala of both alcohol-dependent and non-dependent male rats. Rats were made dependent through chronic intermittent exposure to alcohol vapor and were tested for the acute effect of HCRT-R1-selective (SB-408124; SB-R1), HCRT-R2-selective (NBI-80713; NB-R2), or dual HCRT-R1/2 (NBI-87571; NB-R1/2) antagonism on alcohol intake. NB-R2 and NB-R1/2 antagonists each dose-dependently decreased overall alcohol drinking in alcohol-dependent rats, whereas, SB-R1 decreased alcohol drinking in both alcohol-dependent and non-dependent rats at the highest dose (30 mg/kg). SB-R1, NB-R2, and NB-R1/2 treatment did not significantly affect water drinking in either alcohol-dependent or non-dependent rats. Additional PCR analyses revealed a significant decrease in Hcrtr1 mRNA expression within the central amygdala (CeA) of dependent rats under acute withdrawal conditions compared to nondependent rats. Lastly, a shRNA-encoding adeno-associated viral vector with retrograde function was used to knockdown HCRT in CeA-projecting neurons from the lateral hypothalamus (LH). LH-CeA HCRT knockdown significantly attenuated alcohol self-administration in alcohol-dependent rats. These observations suggest that HCRT signaling in the CeA is necessary for alcohol-seeking behavior during dependence. Together, these data highlight a role for both HCRT-R1 and -R2 in dependent alcohol-seeking behavior.

Fentanyl is a potent synthetic opioid that has been shown to produce sleep disturbances, and the deterioration of sleep quality is associated with drug abuse and relapse in humans. The hypocretin/orexin neuropeptide system is a plausible pharmacological target, and dual-hypocretin antagonists such as lemborexant may mitigate sleep disturbances associated with fentanyl dependence. The current study characterizes sleep macroarchitecture (time spent asleep or awake) and microarchitecture (the number of bouts, and NREM sleep spindle characterization) prior to fentanyl vapor exposure (baseline), following one week of drug abstinence, and four weeks of drug abstinence in female and male rats. Females and males showed a reduction in the amount of time spent in rapid eye movement (REM) sleep following one week of abstinence. The pre-treatment of lemborexant the following day increased the amount of time spent in REM, compared to vehicle at both one and four weeks of abstinence. While there was no effect of fentanyl abstinence on the amount of time spent in non-rapid eye movement (NREM) sleep and wakefulness, lemborexant increased the amount time spent in NREM and decreased the amount of time spent awake. Examination of microarchitecture demonstrated a decrease in the number of NREM bouts at one week of abstinence, which lemborexant subsequently brought back to baseline levels at weeks one and four. Abstinence from fentanyl did not impact the number of NREM sleep spindles, but indicated a trend showing a decrease in intra-spindle frequency at one week of abstinence. Lemborexant, however, increased the number of spindles at weeks one and four of abstinence. Presently, findings indicate that fentanyl abstinence produces changes in sleep macroarchitecture, particularly REM sleep disruptions, which may be alleviated by lemborexant. This highlights the need for further examination of the relationship between sleep disturbances and drug abstinence, and the use of dual-hypocretin antagonists as therapeutic intervention.

Hypocretin/Orexin (HCRT) neurotransmission facilitates drug-seeking behavior. HCRT neurotransmission at HCRT-receptors 1 and 2 (HCRT-R1 and -R2, respectively) is implicated in addiction. During the shift to alcohol-dependency, adaptations in neurotransmitter systems occur in reward- and stress-related brain regions. Specifically, neurotransmission systems in the central amygdala (CeA) are modulated by alcohol drinking/exposure. Therefore, this study investigated Hcrtr1 and Hcrtr2 mRNA expression in the CeA of alcohol-dependent rats and in non-dependent controls during acute alcohol withdrawal. Fos mRNA expression in the CeA of alcohol-dependent and non-dependent rats was also determined to assess adaptations in neuronal activation. To our knowledge, this is the first study to utilize RNAscope to quantify Hcrtr1 and Hcrtr2 mRNA in a rodent model of alcohol dependence. However, Hcrtr1, Hcrtr2, and Fos mRNA levels were not found to be significantly different in alcohol-dependent rats compared to non-dependent controls, possibly due to the temporal dynamics of these neuroadaptations.

No description available.

Retrograde tract tracing combined with immunohistochemical techniques were used to identify the origin of orexin A-immunoreactive (OrA-ir) fibers in the rat medulla. One to 5 days following injection of the fluorescent dye Fluorogold into the dorsal medulla, labeled neurons were found in the lateral half of the lateral hypothalamus, paraventricular, perifornical, dorsomedial, dorsal and posterior hypothalamic nuclei. Labeling the same sections with OrA antisera revealed a concentration of OrA-ir neurons in the perifornical and dorsomedial regions of the tuberal hypothalamus. A maximum of 10% of Fluorogold-labeled hypothalamic neurons were OrA-ir and 15% of OrA-ir hypothalamic neurons contained Fluorogold. Our results demonstrate that a fraction of OrA-ir neurons in the tuberal hypothalamus project to areas of the medulla that are involved in autonomic functions.