Hypocretin-2-Saporin Lesions of the Lateral Hypothalamus Produce Narcoleptic-Like Sleep Behavior in the Rat

Abstract

Hypocretins (Hcrts) are recently discovered peptides linked to the human sleep disorder narcolepsy. Humans with narcolepsy have decreased numbers of Hcrt neurons and Hcrt-null mice also have narcoleptic symptoms. Hcrt neurons are located only in the lateral hypothalamus (LH) but neither electrolytic nor pharmacological lesions of this or any other brain region have produced narcoleptic-like sleep, suggesting that specific neurons need to be destroyed. Hcrt neurons express the Hcrt receptor, and to facilitate lesioning these neurons, the endogenous ligand hypocretin-2/orexin B (Hcrt2) was conjugated to the ribosome-inactivating protein saporin (SAP). In vitro binding studies indicated specificity of the Hcrt2-SAP because it preferentially bound to Chinese hamster ovary cells containing the Hcrt/orexin receptor 2 (HcrtR2/OX(2)R) or the Hcrt/orexin receptor 1 (HcrtR1/OX(1)R) but not to Kirsten murine sarcoma virus transformed rat kidney epithelial (KNRK) cells stably transfected with the substance P (neurokinin-1) receptor. Administration of the toxin to the LH, in which the receptor is known to be present, eliminated some neurons (Hcrt, melanin-concentrating hormone, and adenosine deaminase-containing neurons) but not others (a-melanocyte-stimulating hormone), indicating specificity of the toxin in vivo. When the toxin was administered to the LH, rats had increased slow-wave sleep, rapid-eye movement (REM) sleep, and sleep-onset REM sleep periods. These behavioral changes were negatively correlated with the loss of Hcrt-containing neurons but not with the loss of adenosine deaminase-immunoreactive neurons. These findings indicate that damage to the LH that also causes a substantial loss of Hcrt neurons is likely to produce the multiple sleep disturbances that occur in narcolepsy.

Habenular kisspeptin modulates fear in the zebrafish

“…Three days after Kiss1-SAP administration, c-fos mRNA levels significantly decreased in the vHb and the MR, whereas Kiss1 immunoreactivity decreased only after 12 d. This indicates successful suppression of Kiss1, and in addition, it shows that the efficacy of Kiss1-SAP is different at the level of neural activity and death of Kiss1 neurons. That the incomplete ablation of Kiss1 immunoreactivity is a time course effect is also seen in hypocretin 2-SAP-treated rats (20). In our real-time PCR assay, we noted a high basal level of c-fos mRNA in the Blank-SAP and Kiss1-SAP injected fish, which could be partly a result of the inclusion of the dHb, as the whole habenula was used for mRNA quantification.…”

Cardiovascular effects of hypocretin-1 in nucleus of the solitary tract

“…On the other hand, the Hcrt projections to the NTS may function to modulate the activity of visceral afferents and/or to provide a general activation of the parasympathetic system during the digestive and absorptive phases of ingestion. However, it is now clear that orexin systems are not only involved in ingestive behaviors, but also exert an effect on a variety of physiological mechanisms involved in homeostasis (3,13,19,21,23,25,42,44,45,48). Therefore, it is possible that orexigenic pathways may function to adjust cardiovascular responses to activation of these different homeostatic mechanisms (10,12,15,33,42).…”

“…Although both Hcrt-1 and -2 have been shown to have similar physiological effects when administered centrally, Hcrt-1 appears to exert a more potent effect on most of these physiological variables (10,12,33,42,47). Hcrt-1 injections into the brain have been shown to increase feeding and drinking behaviors; produce sleep, wakefulness, and arousal disturbances; produce analgesia; activate the hypothalamic-pituitary axis; elicit gastric acid secretion; and alter temperature regulating mechanisms (3,14,19,21,23,25,42,44,45,48). Hcrt-1 neurons have been shown to contribute to an extensive innervation of forebrain, brain stem, and spinal cord structures (10,33,42,46,47), and receptors to Hcrt-1 have been demonstrated throughout the neuraxis (28).…”

Effect of microdialysis perfusion of 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol in the perifornical hypothalamus on sleep–wakefulness: Role of δ-subunit containing extrasynaptic GABAA receptors

“…For example, local administration of orexin in various brain regions produced wakefulness (Bourgin et al, 2000;Thakkar et al, 2001;Xi et al, 2001;Methippara et al, 2000). In contrast, a deficiency or reduction of orexinergic neurotransmission resulted in a reduction in wakefulness and cataplexy like episodes in rodents (Lin et al, 1999;Chen et al, 2006;Gerashchenko et al, 2001;Chemelli et al, 1999;Thakkar et al, 1999) and narcolepsy in humans (Thannickal et al, 2000;Mignot, 2004). Single unit recording studies suggest that the orexin neurons exhibited the Wake-On/REM -Off discharge pattern (W>nonREM<REM) (Alam et al, 2002;Lee et al, 2005;Mileykovskiy et al, 2005).…”