Preoptic projections to Barringon's nucleus and the pericoerulear region: Architecture and terminal organization

Abstract

The medial preoptic area (MPO), a sexually dimorphic region, plays a pivotal role in neuroendocrine function and reproductive behavior. We recently reported that MPO projects heavily to the midbrain periaqueductal gray (PAG). We also noted that MPO projects to the dorsolateral pontine tegmentum. Here we identified the cells of origin of the MPO-->tegmental projection and delineated the terminal organization of MPO projections to Barrington's nucleus, locus coeruleus (LC), and the rostromedial pericoerulear region (pLCrm). Correlative cyto- and chemoarchitectonic studies were done to define better the nuclear groups of the dorsolateral pontine tegmentum. Retrograde tracing revealed that MPO neurons projecting to the dorsolateral pontine tegmentum are preferentially distributed in distinct subregions of MPO, including the sexually dimorphic medial preoptic nucleus (MPN). Anterograde tracing with wheat germ agglutinin-horseradish peroxidase or Phaseolus vulgaris leucoagglutinin demonstrated considerable target specificity in projections from MPO to the dorsolateral pontine tegmentum. Barrington's nucleus receives a dense focal input along its entire rostrocaudal axis. In addition, pLCrm is heavily targeted by MPO inputs; pLCrm contains a concentrated plexus of extranuclear dendrites of LC neurons. The lateral dorsal tegmental (LDT) nucleus and LC proper receive only sparse input from MPO. MPO projections to Barrington's nucleus could regulate micturition reflexes during reproductive behavior. The MPO-->pLCrm projection could influence noradrenergic LC neurons in relation to reproductive and/or gonadal steroid function. Given the strong established connections from olfactory structures to MPO, it is possible that the MPO-->LC pathway provides an anatomical substrate for olfactory modulation of arousal.

Medial preoptic area afferents to periaqueductal gray medullo-output neurons: a combined Fos and tract tracing study

“…As shown in Figure 4A, the stimulation site essentially bisected the core of the PHA-L deposit in MPO. Taken together with the finding that this injection produced a dense anterograde labeling in PAG (described below) in a pattern identical to that produced by injections restricted to the central part of MPO (Rizvi et al, 1992(Rizvi et al, , 1994, we conclude that the injection site was centered in MPO.…”

“…A 2.5% solution of PHA-L dissolved in 10 mM PB, pH 8.0, was deposited iontophoretically (+5.0 lus\ constant current pulses, 7 set on, 3 set off duty cycle for 20-30 min) into MPO from a glass micropipette (lo-12 pm tip diameter) as described previously (Rizvi et al, 1992(Rizvi et al, , 1994. Typically, two injections (7.65-7.75 mm ventral to the skull surface), separated dorsoventrally by 300 Frn, were made to increase the size of PHA-L deposit.…”

The region of the pontine parabrachial nucleus is a major target of dehydration-sensitive CRH neurons in the rat lateral hypothalamic area

“…The region medial and ventromedial to the medial aspect of the superior cerebellar peduncle consists of the pontine central gray, the dorsomedial borders of the mesencephalic sensory nucleus of the trigeminal nerve (MEV) and Barrington's nucleus, the lateral tegmental nucleus, the rostral part of the pericoerulear region, and includes the lateral dorsal tegmental area of Rizvi et al (1994). It is a very complex zone, containing afferent axon terminals and dendrites extending out from the locus coeruleus and MEV (Swanson, 1976;Rizvi et al, 1994;Shipley et al, 1996).…”

Projections from bed nuclei of the stria terminalis, magnocellular nucleus: Implications for cerebral hemisphere regulation of micturition, defecation, and penile erection

“…This region sends no direct projections to the sacral spinal cord (Schwanzel-Fukuda et al, 1984;Simerly and Swanson, 1988), but does innervate densely Barrington's nucleus (Rizvi et al, 1994;Ding et al, 1999), and the caudal raphé and adjacent reticular formation (Hermann et al, 1997).…”