The Interaction Between the Ventrolateral Preoptic Nucleus and the Tuberomammillary Nucleus in Regulating the Sleep-Wakefulness Cycle

Abstract

The ventrolateral preoptic nucleus (VLPO) in the anterior hypothalamus and the tuberomammillary nucleus (TMN) in the posterior hypothalamus are critical regions which involve the regulation of sleep-wakefulness flip-flop in the central nervous system. Most of the VLPO neurons are sleep-promoting neurons, which co-express γ-aminobutyric acid (GABA) and galanin, while TMN neurons express histamine (HA), a key wake-promoting neurotransmitter. Previous studies have shown that the two regions are innervated between each other, but how to regulate the sleep-wake cycle are not yet clear. Here, bicuculline (Bic), a GABA _A -receptor antagonist, L-glutamate (L-Glu), an excitatory neurotransmitter, and triprolidine (Trip), a HA₁ receptor (HRH₁) inhibitor, were bilaterally microinjected into TMN or VLPO after surgically implanting the electroencephalogram (EEG) and electromyography (EMG) electrode recording system. Microinjecting L-Glu into VLPO during the night significantly increased the NREM sleep time, and this phenomenon was weakened after selectively blocking GABA _A receptors with Bic microinjected into TMN. Those results reveal that VLPO neurons activated, which may inhibit TMN neurons inducing sleep via GABA _A receptors. On the contrary, exciting TMN neurons by L-Glu during the day, the wakefulness time was significantly increased. These phenomena were reversed by blocking HRH₁ with Trip microinjected into VLPO. Those results reveal that TMN neuron activating may manipulate VLPO neurons via HRH₁, and induce wakefulness. In conclusion, VLPO GABAergic neurons and TMN histaminergic neurons may interact with each other in regulating the sleep-wake cycle.

Keywords: GABAA-receptor; HRH1; L-glutamate; TMN; VLPO; bicuculline; sleep-wake circuitry.

FIGURE 1

The sleep-wakefulness cycle was influenced by injecting L-Glu into VLPO which could be blocked by injecting Bic into TMN. (A) Top: Schematic drawing of the location of drug injection, or aCSF into the VLPO/TMN of a rat (Red: aCSF/L-Glu into VLPO, Yellow: aCSF/Bic into TMN). Bottom: Representative traces of EEG and EMG with drug injected. Drugs were applied at 22:00 (red line), and PSG recording started from 20:00 and lasted for 24 h. (B) Time-course changes of the sleep-wakefulness cycle in rat administration with L-Glu into VLPO. (C) Time-course changes of the sleep-wakefulness cycle in rat administration with L-Glu into VLPO and Bic into TMN. Data were presented as mean ± SEM. The paired t-test was used in the statistical comparisons of two groups. *p < 0.05, **p < 0.01 is compared between two groups at the same time. The arrow shows the time of microinjection.

FIGURE 2

The 5 h cumulative amount of wakefulness, REM and NREM sleep, and TST after administration of aCSF or drugs into the TMN and VLPO of rats. (A) The 5 h cumulative amount of wakefulness. (B) The 5 h cumulative amount of REM sleep. (C) The 5 h cumulative amount of NREM sleep. (D) The 5 h cumulative amount of TST. Data were presented as mean ± SEM. The paired t-test was used in the statistical comparisons of two groups. Compared with the night group of VLPO + aCSF and TMN + aCSF group, **p < 0.01. Compared with the night group of VLPO + L-Glu and TMN + aCSF group, ^#p < 0.05, ^##p < 0.01. V, VLPO; T, TMN; G, L-Glu; B, Bic; a, aCSF.

FIGURE 3

The 5 h cumulative amounts of wakefulness, REM and NREM sleep, and TST after administration of aCSF or drugs into the TMN and VPO of rats. (A) The 5 h cumulative amount of wakefulness. (B) The 5 h cumulative amount of REM sleep. (C) The 5 h cumulative amount of NREM sleep. (D) The 5 h cumulative amount of TST. Data were presented as mean ± SEM. The paired t-test was used in the statistical comparisons of two groups. Compared with the day group of VLPO + aCSF and TMN + aCSF, **p < 0.01; Compared with the day group of VLPO + aCSF and TMN + L-Glu, ^#p < 0.05, ^##p < 0.01. V, VLPO; T, TMN; G, L-Glu; B, Bic; a, aCSF.

FIGURE 4

The sleep-wakefulness cycle was influenced by injecting L-Glu into TMN which could be blocked by injecting Trip into VLPO. (A) Top: Schematic drawing of the location of drug injection, or aCSF into the VLPO/TMN of a rat (Red: aCSF/Trip into VLPO, Yellow: aCSF/L-Glu into TMN). Bottom: Representative traces of EEG and EMG with drug injected. Drugs were applied at 10:00 (red line), and polysomnography recording started from 08:00 and lasted for 24 h. (B) Time-course changes of the sleep-wakefulness cycle in rat administration with L-Glu into TMN. (C) Time-course changes of the sleep-wakefulness cycle in rat administration with L-Glu into TMN and Trip into VLPO. Data were presented as mean ± SEM. The paired t-test was used in the statistical comparisons of two groups. *p < 0.05, **p < 0.01, ***p < 0.001 is compared between two groups at the same time. The arrow shows the time point of microinjection.