Olfactory inputs to hypothalamic neurons controlling reproduction and fertility.

In order to gain insight into sensory processing modulating reproductive behavioral and endocrine changes, we have aimed at identifying afferent pathways to neurons synthesizing luteinizing hormone-releasing hormone (LHRH, also known as gonadotropin-releasing hormone [GnRH]), a key neurohormone of reproduction. Injection of conditional pseudorabies virus into the brain of an LHRH::CRE mouse line led to the identification of neuronal networks connected to LHRH neurons. Remarkably, and in contrast to established notions on the nature of LHRH neuronal inputs, our data identify major olfactory projection pathways originating from a discrete population of olfactory sensory neurons but fail to document any synaptic connectivity with the vomeronasal system. Accordingly, chemosensory modulation of LHRH neuronal activity and mating behavior are dramatically impaired in absence of olfactory function, while they appear unaffected in mouse mutants lacking vomeronasal signaling. Further visualization of afferents to LHRH neurons across the brain offers a unique opportunity to uncover complex polysynaptic circuits modulating reproduction and fertility.

Neurons of the rat preoptic area and the raphe pallidus nucleus innervating the brown adipose tissue express the prostaglandin E receptor subtype EP3.

The major effector organ for thermogenesis during inflammation or experimental pyrogen-induced fever in rodents is the brown adipose tissue (BAT). Prostaglandin E2 (PGE2) microinjection into the medial preoptic area (POA) of rats leads to hyperthermia through an increase in BAT thermogenesis and induces pyrogenic signal transmission towards the raphe pallidus nucleus (RPa), a brainstem nucleus known to contain sympathetic premotor neurons for BAT control. The medial POA has a high expression of prostaglandin E receptor subtype EP3 (EP3R) on POA neurons, suggesting that these EP3R are main central targets of PGE2 to mediate BAT thermogenesis. To reveal central command neurons that contain EP3R and polysynaptically project to the BAT, we combined EP3R immunohistochemistry with the detection of transneuronally labelled neurons that were infected after injection of pseudorabies virus into the BAT. Neurons double-labelled with EP3R and viral surface antigens were particularly numerous in two brain regions, the medial POA and the RPa. Of all medial POA neurons that became virally infected 71 h after BAT inoculation, about 40% expressed the EP3R. This subpopulation of POA neurons is the origin of a complete neuronal chain that connects potential PGE2-sensitive POA neurons with the BAT. As for the efferent pathway of pyrogenic signal transmission, we hypothesize that neurons of this subpopulation of EP3R expressing POA neurons convey their pyrogenic signals towards the BAT via the RPa. We additionally observed that two-thirds of those RPa neurons that polysynaptically project to the interscapular BAT also expressed the EP3R, suggesting that RPa neurons themselves might possess prostaglandin sensitivity that is able to modulate BAT thermogenesis under febrile conditions.

Sympathetic-related neurons in the preoptic region of the rat identified by viral transneuronal labeling.

The viral transneuronal labeling method was used to localize sympathetic-related neurons in the preoptic region following pseudorabies virus (PRV) injections into either the superior cervical ganglion, stellate ganglion, celiac ganglion, or adrenal gland of rats. A general pattern of infection was detected. First, neuronal labeling was found in the medial preoptic area, medial preoptic nucleus, median preoptic nucleus, and lateral preoptic area, and then it spread to the anteroventral periventricular, anteroventral preoptic, and parastrial nuclei. Finally, the forebrain circumventricular organs: organum vasculosum of the lamina terminalis (OVLT) and subfornical organ (SFO) became infected. Neuropeptide-containing preoptic neurons were analyzed following PRV injections in the stellate ganglion. Some thyrotropin-releasing hormone and neurotensin neurons were labeled, but none of the calcitonin gene-related peptide, cholecystokinin, corticotropin-releasing factor, galanin, luteinizing hormone-releasing hormone, enkephalin, substance P, or tyrosine hydroxylase neurons were PRV infected. Two major sympathetic networks appear to be represented in the preoptic region. One is linked to the OVLT, SFO, and anteroventral third ventricular (AV3V) region, sites previously implicated in fluid and electrolyte balance as well as cardiovascular control. The other descending sympathetic pathway appears to target the medial preoptic nucleus as its key nodal point, receiving inputs from infralimbic cortex and limbic regions, such as the lateral septum, medial nucleus of the amygdala, subiculum, and amygdalohippocampal area, and then, projecting caudally to the hypothalamus and brainstem. This second sympathetic network may subserve affiliative, defensive and sexual behaviors.

Efferent connections of the lamina terminalis, the preoptic area and the insular cortex to submandibular and sublingual gland of the rat traced with pseudorabies virus.

Neurones situated in the lamina terminalis (organum vasculosum of the lamina terminalis, median preoptic nucleus and subfornical organ) as well as within medial and lateral parts of the preoptic area and in the insular cortex become transneuronally labelled following pseudorabies virus injections into the submandibular or the sublingual gland. These neurones are efferently connected to a chain of central neurones directed to secretory or vascular tissue of the submandibular or the sublingual gland. By varying the postinoculation time a stepwise infection of different forebrain nuclei was registered, with the hypothalamic paraventricular nucleus and the lateral hypothalamic area being the first forebrain structures labelled. Such early infected neurones within these hypothalamic nuclei are in all likelihood third order neurones regulating salivary secretion and might have functioned as relays transmitting virus to other forebrain structures. The above mentioned forebrain areas together with several other hypothalamic nuclei as well as the bed nucleus of the stria terminalis, the central nucleus of the amygdala and the substantia innominata, seem to be the widespread anatomical basis for the central regulation of salivary gland function.