Sleep is related to neuron numbers in the ventrolateral preoptic/intermediate nucleus in older adults with and without Alzheimer's disease

Abstract

Fragmented sleep is a common and troubling symptom in ageing and Alzheimer's disease; however, its neurobiological basis in many patients is unknown. In rodents, lesions of the hypothalamic ventrolateral preoptic nucleus cause fragmented sleep. We previously proposed that the intermediate nucleus in the human hypothalamus, which has a similar location and neurotransmitter profile, is the homologue of the ventrolateral preoptic nucleus, but physiological data in humans were lacking. We hypothesized that if the intermediate nucleus is important for human sleep, then intermediate nucleus cell loss may contribute to fragmentation and loss of sleep in ageing and Alzheimer's disease. We studied 45 older adults (mean age at death 89.2 years; 71% female; 12 with Alzheimer's disease) from the Rush Memory and Aging Project, a community-based study of ageing and dementia, who had at least 1 week of wrist actigraphy proximate to death. Upon death a median of 15.5 months later, we used immunohistochemistry and stereology to quantify the number of galanin-immunoreactive intermediate nucleus neurons in each individual, and related this to ante-mortem sleep fragmentation. Individuals with Alzheimer's disease had fewer galaninergic intermediate nucleus neurons than those without (estimate -2872, standard error = 829, P = 0.001). Individuals with more galanin-immunoreactive intermediate nucleus neurons had less fragmented sleep, after adjusting for age and sex, and this association was strongest in those for whom the lag between actigraphy and death was <1 year (estimate -0.0013, standard error = 0.0005, P = 0.023). This association did not differ between individuals with and without Alzheimer's disease, and similar associations were not seen for two other cell populations near the intermediate nucleus. These data are consistent with the intermediate nucleus being the human homologue of the ventrolateral preoptic nucleus. Moreover, they demonstrate that a paucity of galanin-immunoreactive intermediate nucleus neurons is accompanied by sleep fragmentation in older adults with and without Alzheimer's disease.

Keywords: Alzheimer’s disease; human; hypothalamus; intermediate nucleus; sleep.

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Figures

Figure 1

The intermediate nucleus of the hypothalamus. (A) Representative low power view of the anterior hypothalamus stained immunohistochemically for galanin. The box indicates the counting frame used to define the intermediate nucleus. The long axis of the box is parallel to the lateral wall of the third ventricle. The inferomedial corner of the box is at the midpoint of a line, parallel to the base of the brain, connecting the angle between the base of the brain and the chiasmatic region inferolateral to the supraoptic nucleus to the lateral wall of the third ventricle. 3V = third ventricle; IN = intermediate nucleus; DBB = nucleus of the diagonal band of Broca; OT = optic tract; OC = optic chiasm. (B) Representative high power view of intermediate nucleus of the hypothalamus stained for galanin.

Figure 2

The presence of Alzheimer’s disease (AD) is associated with fewer galanin-immunoreactive neurons in the intermediate nucleus (IN) (n = 45).

Figure 3

The number of galanin-immunoreactive neurons in the intermediate nucleus is associated with sleep fragmentation as assessed by actigraphy. (A) Association between galanin-immunoreactive neuron counts and sleep fragmentation in subjects who died within 1 year of actigraphy (n = 19). (B) Participants who died over 1 year after actigraphy (n = 26). All panels show partial regression plots of models adjusted for age, sex, and presence/absence of Alzheimer’s disease. r indicates the partial correlation coefficient between the number of galanin-immunoreactive neurons and sleep fragmentation measured using kRA. Briefly, kRA is the probability per 15-s epoch of having an arousal, as indicated by movement (defined as a non-zero activity count) after a long (about ≥5 min) period of rest (i.e. sleep), with a higher kRA indicating greater sleep fragmentation. The association between the number of galanin-immunoreactive neurons and actigraphically measured sleep fragmentation is significantly stronger the shorter the time lag between actigraphy and death (interaction P = 0.019). Gal = galanin; IN = intermediate nucleus.

Figure 4

The association between number of galanin-immunoreactive neurons in the intermediate nucleus and sleep fragmentation does not differ by the presence/absence of Alzheimer's disease. (A) Association between galanin-immunoreactive neuron counts and sleep fragmentation considering participants without Alzheimer’s disease who died within 1 year of actigraphy (n = 13). (B) Participants with Alzheimer’s disease who died within 1 year of actigraphy (n = 6). All panels show partial regression plots of models adjusted for age and sex. r indicates the partial correlation coefficient between the number of galanin-immunoreactive neurons and sleep fragmentation measured using kRA. The association between the number of galanin-immunoreactive neurons and sleep fragmentation does not differ in those with and without Alzheimer’s disease (interaction P = 0.64). AD = Alzheimer’s disease; Gal = galanin; IN = intermediate nucleus.

Figure 5

Secondary outcomes. We considered a number of secondary outcomes in participants with and without Alzheimer’s disease who died within 12 months of their actigraphic recordings. (A) Total hours per day spent in bouts of rest of 10 min duration or longer (n = 19). (B) Proportion of total rest time spent in bouts ≥10 min (n = 19). All panels show partial regression plots of models adjusted for age and sex. r indicates the partial correlation coefficient between the number of galanin-immunoreactive neurons and the indicated outcome. Abbreviations: Gal = galanin; IN = intermediate nucleus.

Figure 6

The numbers of AVP-immunoreactive and VIP-immunoreactive neurons in the suprachiasmatic nucleus are not associated with sleep fragmentation as assessed by actigraphy. (A) VIP-immunoreactive suprachiasmatic nucleus neuron counts (n = 22). (B) AVP-immunoreactive suprachiasmatic nucleus neuron counts (n = 22). All panels show partial regression plots of models adjusted for age, sex, and presence/absence of Alzheimer's disease. r indicates the partial correlation coefficient between the number of neurons and sleep fragmentation measured using kRA). SCN = suprachiasmatic nucleus.