Narp immunostaining of human hypocretin (orexin) neurons: loss in narcolepsy

Abstract

Objective: To investigate whether neuronal activity-regulated pentraxin (Narp) colocalizes with hypocretin (Hcrt or orexin) in the normal human brain and to determine if Narp staining is lost in the narcoleptic human brain.

Background: Human narcolepsy is characterized by a loss of the peptide hypocretin in the hypothalamus. This loss could result from the degeneration of neurons containing hypocretin or from a more specific loss of the ability of these neurons to synthesize Hcrt. Narp has been found to colocalize with hypocretin in the rat hypothalamus.

Methods: We investigated the distribution of Narp in three normal and four narcoleptic human postmortem brains using immunohistochemistry with an antibody to Narp. Colocalization studies of Narp and hypocretin were also performed in two normal brains using immunohistochemistry with an antibody to Narp and an antibody to hypocretin.

Results: We found that Narp colocalizes with hypocretin in the lateral hypothalamic area (LHA), the dorsomedial hypothalamus (DMH), the dorsal hypothalamic area (DHA), and the posterior hypothalamic area (PHA) of the normal human. The number of Narp-positive neurons was reduced by 89% in these areas of the narcoleptic hypothalamus. In contrast, Narp staining in the paraventricular (Pa) and supraoptic nuclei (SO) of the human hypothalamus did not differ between normal and narcoleptic brains.

Conclusions: This finding supports the hypothesis that narcolepsy results from the specific loss of hypocretin neurons. Loss of hypothalamic Narp may contribute to the symptoms of narcolepsy.

Figure 1.

Narp staining with DAB in the LHA, DMH, DHA, and PHA of narcoleptic and control tissue. Left column shows low-power images of matched normal and narcoleptic LHA, DMH, DHA, and PHA. Middle and right columns show increasingly higher power images of the same area shown in the left column. Scale bars in each column apply to all panels below and within the same column.

Figure 2.

Narp staining in the SO and Pa of narcoleptic and control sections. Left column shows low-power images of the SO and Pa of matched normal and narcoleptic sections. Middle and right columns show increasingly higher-power images of the same area shown in the left column. 3V = third ventricle; opt = optic tract. Scale bars in each column apply to all panels below and within the same column.