Katuya Zyo

Comparative anatomical study of the tegmentomammillary projections in some mammals: a horseradish peroxidase study.

Mammillary projections from each subnuclei of Gudden s tegmental nuclei were investigated by retrograde transport of horseradish peroxidase (HRP) in the cat, rat, guinea pig, golden hamster and house shrew (Suncus murinus, Insectivora). The dorsal tegmental nucleus of Gudden (TD) is composed of the pars dorsalis (TDD) and the pars ventralis ( TDV ) in the cat, rat, guinea pig, and golden hamster, but the TD of the house shrew can not be divided. The ventral tegmental nucleus of Gudden (TV) is composed of the pars principalis (TVP) and the pars suprafascicularis ( TVS ) in the golden hamster and house shrew, but the TVS is not recognized in the cat, rat and guinea pig. The TDV projects to the lateral mammillary nucleus, and the TVP projects to the medial mammillary nucleus ipsilaterally in the cat, rat, guinea pig and golden hamster. The TVS of the golden hamster projects to the medial mammillary nucleus. The TVP and TVS of the house shrew project to the medial mammillary nucleus, and the TVS also to the lateral mammillary nucleus. In addition, the pars compacta of the nucleus centralis superior projects to the medial mammillary nucleus in the rat, guinea pig and golden hamster. However, the TDD sends no fibers to the mammillary nuclei in these 5 species of mammals.

Neuroanatomical study of afferent projections to the supramammillary nucleus of the rat

We examined the regions projecting to the supramammillary nucleus of the rat with retrograde transport of WGA-HRP and WGA, and anterograde transport of Phaseolus vulgaris leucoagglutinin. The supramammillary nucleus receives major descending afferents from the infralimbic cortex, the dorsal peduncular cortex, the nucleus of the diagonal band of Broca, the medial and lateral preoptic nuclei, bilaterally. The major ascending afferents come from the pars compacta of the nucleus centralis superior, the ventral tegmental nucleus, and the laterodorsal tegmental nucleus. The supramammillary nucleus also receives a few (but distinct) fibers from the anterior and lateral hypothalamic nuclei, the ventral premammillary nucleus, the interpeduncular nucleus, the cuneiform nucleus, the dorsal raphe nucleus, the incertus nucleus, and the C3 region including the prepositus hypoglossi nucleus. All descending fibers run through the medial forebrain bundle. Almost all ascending fibers from the pars compacta of the nucleus centralis superior and the laterodorsal tegmental nucleus run through the mammillary peduncle, and terminate throughout the supramammillary nucleus. A few fibers from the laterodorsal tegmental nucleus and the C3 region run through the fasciculus longitudinalis dorsalis and terminate in the dorsal part of the supramammillary nucleus including the supramammillary decussation.

Organization of the habenulo-interpeduncular connections in cats: A horseradish peroxidase study

The afferent fiber connections to the interpeduncular (IP) complex were demonstrated by the retrograde axonal transport of horseradish peroxidase (HRP) in cats. The HRP was injected into each nucleus of the IP complex, that is the central nucleus (IPC), the paramedian nucleus (IPP), the apical nucleus (IPA), and the posterior nucleus (IPN) including the outer division (IPO) and the inner division (IPI), and surrounding areas of the IP complex, using a ventral or dorsal surgical approaches. Most of the labeled neurons were in the medial habenular nucleus (MH) and each of the sub-nuclei of the IP complex was related to a specific part of the MH. Thus, the mediodorsal part of MH projected to the IPC, the medioventral part of MH projected to the IPI, the laterodorsal part of MH projected to the IPA, and the lateroventral part of MH projected to the IPP and the IPO. There were a few labeled cells in the accessory dorsal tegmental nucleus, the nucleus raphe dorsalis (RD), the nucleus centralis superior, the nucleus of the locus coeruleus, the gray matter of the floor of the fourth ventricle, and the nucleus of diagonal band of Broca, but there were no obvious patterns in the projections of these nuclei to the different sub-nuclei of the IP complex. When the area of the HRP injection involved the midbrain reticular formation adjacent to the IP complex and the nucleus reticularis tegmenti pontis (RT) but not the IP complex itself, there were many labeled cells in the lateral habenular nucleus and the medial and lateral mammillary nuclei, but there were no labeled cells in the medial habenular nucleus.

Ultrastructural study of ascending projections to the lateral mammillary nucleus of the rat.

SummaryWe examined the synaptic organization of ascending projections from the pars ventralis of the dorsal tegmental nucleus of Gudden (TDV) and the laterodorsal tegmental nucleus to the lateral mammillary nucleus (LM). The LM neuropil consists of terminals containing pleomorphic synaptic vesicles and forming symmetric synaptic contact, and terminals containing round synaptic vesicles and forming asymmetric synaptic contact. They make up 63% and 37%, respectively, of all axodendritic terminals. All axosomatic terminals contain pleomorphic vesicles and make symmetric contact. Following injection of WGA-HRP into the TDV, many anterogradely labeled terminals and retrogradely labeled cells are found in the LM. Labeled terminals contact mainly proximal (more than 2 μm diameter) and intermediate (1–2 μm diameter) dendrites. Serial ultrathin sections of the LM show that 55% of axosomatic terminals are labeled anterogradely. Following injection of WGA-HRP into the laterodorsal tegmental nucleus, many anterogradely labeled terminals are found in the LM, but no retrogradely labeled cells are present. Labeled terminals contact mainly distal (less than 1 μm diameter) and intermediate dendrites as well as somata. In the LM neurons, 46% of axosomatic terminals are labeled anterogradely. All labeled terminals from these nuclei contain pleomorphic vesicles and make symmetric synaptic contact. These results indicate that almost all axosomatic terminals come from the TDV and the laterodorsal tegmental nucleus, which send inhibitory inputs to the lateral mammillary nucleus.

ULTRASTRUCTURAL CHARACTERIZATION OF PHARYNGEAL AND ESOPHAGEAL MOTONEURONS IN THE NUCLEUS AMBIGUUS OF THE RAT

The viscerotopic organization of the upper alimentary tract has been established in the nucleus ambiguus, but there is little information about the morphology of the individual neurons innervating the pharynx and esophagus. We studied the ultrastructure of pharyngeal (PH), cervical esophageal (CE), and subdiaphragmatic esophageal (SDE) motoneurons labeled by retrogradely transported wheat germ agglutinin conjugated horseradish peroxidase (WGA‐HRP) in the compact formation of the nucleus ambiguus. WGA‐HRP was injected into the lower pharynx, or the cervical and subdiaphragmatic esophagus of male rats. The retrogradely labeled PH neurons in the rostral portion of the compact formation were large (26.1 × 50.1 μm, 906.7 μm2), polygonal, and contained well‐developed cell organelles with a round nucleus. Subsurface cisterns connected with rough endoplastic reticulum were often present near the postsynaptic membrane. Both CE and SDE neurons in the compact formation were medium‐sized, round or oval, and contained well‐developed cell organelles, although the SDE neuron was significantly larger than the CE neuron (24.9 × 33.6 μm, 593.0 μm2 in the SDE neuron, and 19.5 × 30.2 μm, 440.3 μm2 in the CE neuron).

Quantitative and ultrastructural study of ascending projections to the medial mammillary nucleus in the rat

SummaryWe analyzed the termination pattern of axons from the superior central nucleus and the ventral tegmental nucleus of Gudden within the medial mammillary nucleus (MM) in the rat. The neuropil of the MM consists of two classes of terminals, that is, terminals containing round synaptic vesicles and forming asymmetric synaptic contact, and terminals containing pleomorphic synaptic vesicles and forming symmetric synaptic contact. The number of axodendritic terminals with round vesicles is almost equal to that of terminals with pleomorphic vesicles. Almost all axosomatic terminals contain pleomorphic vesicles with symmetric synaptic contact. Injection of WGA-HRP into the central part of the superior central nucleus permitted ultrastructural recognition of many anterogradely labeled terminals within the median region of MM. The labeled terminals contacted mainly intermediate (1–2 μm diameter) and proximal dendrites (more than 2 μm diameter) as well as the neuronal somata. Serial ultrathin sections of neurons of the median region of the MM revealed that 37% of the axosomatic terminals were labeled anterogradely. The pars compacta of the superior central nucleus had reciprocal connections with the median region of MM. The axon terminals from this nucleus occupied 53% of axosomatic terminals, and contacted mainly intermediate dendrites. Following injection of WGA-HRP into the ventral tegmental nucleus, many labeled terminals were found in the medial and lateral regions of MM. They contacted mainly intermediate dendrites as well as neuronal somata. In the medial region, 78% of axosomatic terminals contacting retrogradely labeled neurons were labeled anterogradely. All labeled terminals from these nuclei contained pleomorphic vesicles, and made symmetric synaptic contact.

Synaptic organization of afferent projections to the supramammillary nucleus of the rat

We studied the fine structure of afferent terminals from the preoptic area, the nucleus of the diagonal band of Broca, the infralimbic cortex and the laterodorsal tegmental nucleus within the supramammillary nucleus (SUM) using the anterograde tracing method of horse-radish peroxidase conjugated with wheat germ agglutinin (WGA-HRP). Injection of WGA-HRP into the preoptic area permitted ultrastructural recognition of many anterogradely labeled terminals in the SUM. Almost all labeled terminals (99%) contained clear round synaptic vesicles and formed asymmetric synaptic contacts (Grays type I). About 86% of labeled terminals from the nucleus of the diagonal band were asymmetric (Grays type I), whereas 14% contained pleomorphic synaptic vesicles and formed symmetric synaptic contacts (Grays type II). Almost all labeled terminals from the infralimbic cortex were located in the ventral part of the SUM, and 95% of labeled terminals were Grays type I. The majority of labeled terminals (90%) from the laterodorsal tegmental nucleus were Grays type I, and the remaining (10%) were Grays type II. The percentage of labeled terminals with dense-cored vesicles was very high in terminals from the preoptic area (70%), and low in terminals from the infralimbic cortex (19%). Labeled terminals in all cases contacted mainly intermediate-sized dendrites (0.5–1.0 μm diameter). All cases had only a few labeled axosomatic terminals. The cases of injections into the preoptic area and the diagonal band nucleus had some reciprocal connections at the ultrastructural level.

Fine structural survey of Gudden's tegmental nuclei in the rat: cytology and axosomatic synapses

SummaryThe fine structure of neuronal somata and axosomatic synapses in each subnucleus of Guddens tegmental nuclei was studied by use of electron microscopy. The pars principalis of the ventral tegmental nucleus of Gudden (TVP) is composed of oblong or triangular, medium sized neurons (11.8x22.6 μm, 211.4 μm2) containing many mitochondria, lysosomes, Golgi apparatus, and rough endoplasmic reticulum composing Nissl bodies. The light oval nucleus with a prominent nucleolus is centrally situated, and indentations of its nuclear envelope are recognized in all neurons. The neuron in the pars ventralis of the dorsal tegmental nucleus of Gudden (TDV) is similar to that in the TVP, but its average size is significantly smaller (10.0x18.8 μm, 151.4 μm2), and its organelles are also less well developed. The pars dorsalis of the dorsal tegmental nucleus of Gudden (TDD) is composed of spindle shaped, small neurons (6.9x16.2 μm, 85.1 μm2) characterized by their irregular shaped nucleus with its invaginated envelope. These neurons have a thin rim of cytoplasm, poorly developed organelles and no Nissl bodies. The average number of axosomatic terminals in a sectional plane is 9.9 in the TVP, 9.6 in the TDV and 2.6 in the TDD, and the bouton covering ratio is 24.3% in the TVP, 26.5% in the TDV and 7.4% in the TDD. The respective percentages of round, flat and pleomorphic type axosomatic terminals were estimated, and the flat type terminals were found to be dominant in the TVP, the pleomorphic type terminals in the TDV, and the round type terminals in the TDD.

1617 Synaptic organization of afferents from the nucleus tractus solitarii to the esophageal motoneurons in the nucleus ambiguus

To investigate the genesis of respiratory neural rhythm in the mammalian spinal cord, we experimentally induced the spinal respiratory rhythm in rib-attached spinal cord preparations (decerebrated at the upper cervical level) isolated from neonatal rats (0 3 days). Phrenic burst discharges were recorded unilaterally from a phrenic nerve by a suction electrode. Serotonin (54-R, 50 w) was bath-applied for 5 min into the recording chamber with a perfusate (modified Krebs’, 25 27 ‘C). From 1 to 2 minutes after the 5-HT application, tetanic contraction of the rib cage occurred and then followed by rhythmic contraction-relaxations of flexors of neck and the rib cage with a period of 10 30 s. Concomitantly with the muscle contraction-relaxation cycles, the phrenic bursts were recorded with a duration of 5 10 s. These bursts synchronized with the contraction rhythm locked to the relaxation phase. These results clearly demonstrate that the spinal cord has an ability for generating respiratory rhythm.