Preoptic area systems

Figure 2.4 Flip-flop switch model of wake and slow wave sleep active systems. Mutually inhibitory connections exist between GABAergic/Galaninergic slow wave sleep active neurons in the ventrolateral preoptic area (VLPO) of the anterior hypothalamus and aminergic neurons in the hypothalamus (histamine (HA) neurons in the tuberomammillary nucleus (TMN)) and brainstem (serotonin (5-HT) neurons in the dorsal raphe (DR) and noradrenaline (NA) neurons in the locus coeruleus (LC)). Orexinergic neurons in the perifornical hypothalamus (PFH) stabilize the waking state via excitation of the waking side of the flip-flop switch (aminergic neurons).

Table 7.1 Major dopaminergic modulatory systems of the brain. Abbreviations MPO, medial preoptic area.

Immunohistochemical and electrophysiological studies of the hypothalamic preoptic area (POA), which plays a major role in sleep promotion, have identified a subset of sleep-active ventrolateral POA (VLPO) neurons (Sherin et al. 1996 Szymusiak et al. 1998). A tightly clustered group of VLPO neurons appears to promote non-REM sleep, by suppression of the histaminergic arousal system, which... 

By contrast, the accessory olfactory system is thought to be involved in the detection of odors that influence a variety of reproductive and aggressive behaviors (Keverne 1999). Sensory neurons are located in the vomeronasal organ (VNO) and detect pheromones which gain access to the VNO by a pumping mechanism (Meredith and O Connell, 1979). VNO neurons send projections to the accessory olfactory bulb (AOB). Mitral cells of the AOB project in turn to the medial nucleus of the amygdala olfactory information is then dispatched to several hypothalamic regions such as the bed nucleus of the stria terminalis, the medial preoptic area and the ventromedial hypothalamus (Scalia and Winans 1975). 

Swann, Rahaman, F., Bijak, T. and Fiber, J. (2001) The main olfactory system mediates pheromone-induced fos expression in the extended amygdala and preoptic area of the male Syrian hamster. Neuroscience 105, 695-706. 

Angiotensin II produces changes in body hydration and thirst by a direct action in the central nervous system. The administration of angiotensin II into the septal, anterior hypothalamic, and medial preoptic areas stimulates drinking behavior in several species. Part of the volume response also may be caused by the antinatriuretic and antidiuretic effects of angiotensin II. 

Most injection studies have been performed in projection areas of the serotonergic system and in the raph nuclei from which serotonergic fibers emanate. HiUegaart et al. [42] reported that 8-OH-DPAT ii jected into the nucleus accumbens produced a facilitation of the male rat sexual behavioiir, as evidenced by a decrease in number of mounts and intromissions to ejaculation, as well as by a decrease in the postejaculatory interval. Injections into the olfactory tubercle had no effects on sexual behaviour. Femdndez-Guasti et al. [43] confirmed the stimulatory effects of 8-OH-DPAT after local application into the nuclear accumbens, but edso found similar effects for medial preoptic area injections. They foimd no effects after dorsal raph4 administration, in line with HiUegaart et al. 

Figure 2. Schematic diagram of the nasal cavities and forebrain of a salamander, illustrating the central projections of the olfactory and vomeronasal systems in dorsal view. Anterior is toward the top of the figure, and only ipsilateral projections are shown. The medial (A) and lateral (B) olfactory tracts arise from the olfactory bulb. (C) The extra-bulbar ol ctory pathway bypasses the olfactory bulb and projects directly to the anterior preoptic area. (D) The accessory olfactory bulb, which receives input from the vomeronasal organ, projects to the lateral amygdala (la). Other abbreviations apoa = anterior preoptic area dp = dorsal pallium Ip = lateral pallium mp = medial pallium ma = medial amygdala s = septum sir = striatum. Based on descriptions in Hetrick, 1927,1933,1948 Kokoros and Northcutt, 1977 and Schmidt and Roth, 1990.

Studies of c-fos expression in the accessory olfactory system have been performed almost exclusively in the context of sexual behavior of animals (Fiber, Adames Swann, 1993 Schellinck, Smyth, Brown Wilkinson, 1993 Baum, Brown, Kica, Rubin, Johnson Papaioannou, 1994 Femandez-Fewell and Meredith, 1994 Rajendren and Moss, 1994 Bressler and Baum, 1996). Many studies show that c-fos is expressed in the vomeronasal projection circuit (i.e. the anterior olfactory bulb, the medial amygdala, the posterior medial bed nucleus of the stria terminalis, or the medial preoptic area) after mating behavior. Importantly, there have been no reports of specific c-fos expression in the VNO. 

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