Serotonergic innervation of mesencephalic trigeminal nucleus neurons: a light and electron microscopic study in the rat.

Neurons of the mesencephalic trigeminal nucleus (MTN) are considered to be homologous to mechanosensitive neurons in the sensory ganglia. The sites of origin of serotonin (5HT)-immunoreactive axons on neuronal cell bodies in the MTN were studied in the rat by combining immunofluorescence histochemical techniques with retrograde tracing of Fluoro-Gold (FG) and anterograde tracing of biotin-conjugated dextran amine (BDA). The tracing studies, which were combined with multiple-labeling immunohistochemistry and confocal microscopy, indicated that 5HT-immunoreactive axon terminals on the cell bodies of MTN neurons originated from the medullary raphe nuclei, such as the nucleus raphes magmus (RMg), alpha part of the nucleus reticularis gigantocellularis (GiA) and nucleus raphes obscurus (ROb), as well as from the mesopontine raphe nuclei, such as the nucleus raphes dorsalis (DR), nucleus raphes pontis (PnR) and nucleus raphes medianus (MnR); mainly from the RMg, GiA and DR, and additionally from the ROb, PnR and MnR. The cell bodies in close apposition to 5HT-immunoreactive axon terminals were found through the whole rostrocaudal extent of the MTN. Electron microscopically a number of axon terminals that were labeled with BDA injected into the raphe nuclei were confirmed to be in asymmetric synaptic contact with the cell bodies of MTN neurons. It was also indicated that substance P existed in some of the 5HT-containing axosomatic terminals arising from the ROb, RMg and GiA. The present results indicated that proprioceptive sensory signals from the muscle spindles or periodontal ligament might be modulated at the level of the primary afferent cell bodies in the MTN by 5HT-containing axons from the mesopontine and medullary raphe nuclei including the GiA.

Substance P receptor (NK1)-immunoreactive neurons projecting to the periaqueductal gray: distribution in the spinal trigeminal nucleus and the spinal cord of the rat.

Substance P receptor (SPR)-immunoreactive neurons projecting to the periaqueductal gray (PAG) were examined in the rat spinal trigeminal nucleus and spinal cord by a retrograde tracing method combined with immunofluorescence histochemistry. After injection of Fluoro-gold (FG) into the PAG, SPR-immunoreactive neurons labeled with FG were observed mainly in the lateral spinal nucleus and lamina I of the medullary and spinal dorsal horns and additionally in laminae V and X of the spinal cord.

Fos expression in serotonergic midbrain neurons projecting to the paraventricular nucleus of hypothalamus after noxious stimulation of the stomach: a triple labeling study in the rat.

Horseradish peroxidase (HRP) was stereotaxically injected into the paraventricular nucleus of the hypothalamus (PVH) and visceral noxious stimulation was given by an administration of formalin into the stomach. The brain sections were subjected to HRP histochemistry and immunostained with Fos and serotonin antibodies. The periaqueductal gray (PAG) and dorsal raphe nucleus (DR) contained single-labeled (Fos, 5HT, HRP), double-labeled (Fos/HRP, Fos/5HT, HRP/5HT) and triple-labeled (HRP/Fos/5HT) neurons. Triple-labeled neurons were mainly observed in the DR and in discrete areas of the PAG ipsilateral to side of the HRP injection. These findings suggest that a population of serotonergic midbrain neurons receive nociceptive visceral information and project to the PVH.

Medullary catecholaminergic neurons projecting to lateral hypothalamic area and expressing Fos after chemical stimulation of the stomach in the rat.

Catecholaminergic neurons in the medulla projecting to lateral hypothalamic area (LH) and expressing Fos were investigated in the rat by a triple labelling method, in which horseradish peroxidase (HRP) was injected into the LH, and visceral noxious stimulation was induced by formalin injection into the stomach, sections of the medulla were stained histochemically for HRP and immunohistochemically for Fos and tyrosine hydroxylase (TH). Some neurons labeled with HRP and showing both Fos- and TH-like immunoreactivities were mainly found in the nucleus tractus solitarii (NTS) and ventrolateral medulla (VLM) at the middle and caudal levels of medulla, only a few of them were located in the reticular formation between NTS and VLM. These results indicated that some medullary catecholaminergic neurons projected to the LH and some of them might be involved in the transmissing processes of stress responses to the visceral nociceptive information produced by chemical stimulation.

Fos expression in catecholaminergic medullary neurons induced by chemical stimulation of stomach projecting to the paraventricular nucleus of the hypothalamus in rats.

AIM: To determine whether medullary catecholaminergic neurons expressing Fos induced by chemical stimulation of the stomach project to the paraventricular nucleus of hypothalamus (PVH) in rats. METHODS: Horseradish peroxidase (HRP) was introduced stereotaxically into the PVH of rats. Histochemical analysis of coronal sections through the medulla were analyzed using triple-label immunohistochemistry to identify cells that were retrogradely labeled with HRP, Fos (ABC method), and tyrosin hydroxylase (TH) (PAP method). RESULTS: Seven kinds of labeled neurons were found in the nucleus tractus solitarii (NTS), the ventrolateral medulla (VLM) and the reticular formation (RF) of the medulla: Fos-like immunoreactive (FosLI) neurons, TH-like immunoreactive (TH-LI) neurons and HRP retrogradely single-labeled neurons, FosLI/HRP, FosLI/TH-LI and HRP/TH-LI double-labeled neurons, and FosLI/HRP/TH-LI triple-labeled neurons. CONCLUSION: Ascending projections from the NTS, VLM and RF to the PVH might be involved in the transmitting process of visceral noxious stimulation.