Hideo Minagawa

Ontogeny of substance P-containing neuron system of the rat: Immunohistochemical analysis—I. Forebrain and upper brain stem

The ontogeny of substance P-containing neuron system in the forebrain and upper brain stem of the rat was investigated by means of the indirect immunofluorescence technique. Substance P-positive structures first appeared in the primordium of the epithalamus and the area which surrounded the commissura posterior of the rat fetus corresponding to gestational day 14 (10-12 mm embryos). On and after gestational day 14, substance P-positive structures gradually made their appearance in various areas of the forebrain and upper brain stem. Substance P-positive structures thus continued to increase in number and in density during the fetus and perinatal stage and showed histochemically maximum content at the stage between postnatal days 5 and 15. After then, substance P-positive neurons tended to decrease in number as the rats grew, while substance P-positive fibers maintained in general their strong immunoreactivity even in the adult rats. The present study demonstrates that substance P-positive structures appear at a very early ontogenetical stage. This suggests that substance P might play an important role in the development of the forebrain and upper brain stem in addition to its neurotransmitter or neuromodulator functions.

Evidence for the existence of a substance P-containing pathway from the nucleus laterodorsalis tegmenti (Castaldi) to the lateral septal area of the rat.

The existence of a long ascending substance P (SP)-containing neuron system from the nucleus laterodorsalis tegmenti of Castaldi to the lateral septal area was demonstrated in this study. The destruction of the n. laterodorsalis tegmenti resulted in a marked reduction of SP-positive fibers in the ipsilateral lateral septal area.

Ontogeny of neurotensin-containing neuron system of the rat: Immunohistochemical analysis—II. Lower brain stem

The ontogeny of the neurotensin neuron system in the lower brain stem of the rat was investigated by means of indirect immunofluorescent method. Neurotensin-like immunoreactivity-containing cells first appear in the primordium of the n. tractus solitarii, n. tractus spinalis nervi trigemini, reticular formation just medial to the latter nucleus, n. reticularis parvocellularis, n. laterodorsalis tegmenti, and midbrain reticular formation of the fetus at gestational day 17. At gestional day 18, neurotensin-immunoreactive cells newly appear in the n. raphe dorsalis. Between gestational day 19 and postnatal day 7, the animals show a remarkable increase in number of immunoreactive cells and fibers in various lower brain stem areas except for n. tractus spinalis nervi trigemini and n. tractus solitarii. Moreover, during this stage, neurotensin-immunoreactive cells located in the n. prepositus hypoglossi and n. vestibularis lateralis appear for the first time at birth and postnatal day 5, respectively. Since postnatal day 7, although the majority of immunoreactive cells located in the lower brain stem decrease in number as the rats grow, immunoreactive cells in the n. tractus spinalis nervi trigemini, on the contrary, increase in number from after birth until postnatal day 10, and maintain more or less their immunoreactivity even in the adult rat. In addition, neurotensin-immunoreactive cells in the nucleus of the solitary tract increase in number during the fetal period, reach the maximum content at postnatal day 7-10, and maintain their immunoreactivity even in the adult rats. Thus, the present study demonstrated that neurotensin-like immunoreactive structures appear at a very early ontogenetical stage, suggesting that neurotensin plays an important role in the development of the lower brain stem of the rat. In addition, the present study further showed that neurotensin-immuno-reactivity shows various fluctuations during the ontogeny, suggesting multiple functions of neurotensin in the central nervous system.

Pathways and terminal fields of the cochlearofugal somatostatin tracts of very young rats.

The cochlearofugal somatostatin (SRIF) neuron system of very young rats (between newborn and 1 week old) was investigated by means of the indirect immunofluorescence technique of Coons. Cochlear nuclei (both dorsal and ventral cochlear nuclei) of this stage contain numerous SRIF-positive cells which are scarcely found in adult rats. Based upon the experimental findings obtained by this study, the majority of SRIF-positive fibers originating from these nuclei reach the contralateral inferior colliculus via well-established cochlearo-inferior collicular tracts such as dorsal acoustic striae, intermediate acoustic striae and trapezoid body, respectively. The possible significance of SRIF in the development of the auditory system is briefly discussed.

New somatostatin-containing sites in the diencephalon of the neonatal rat

Using an immunohistochemical technique, the present study demonstrated several new somatostatin-containing sites in the diencephalon of neonatal rats which have not been reported in adult animals. These areas are the area just lateral to the commissura posterior, the area between the optic tract and capsula interna, pars retrolenticularis and n. peripeduncularis.

Somatostatin-like immunoreactivity in the facial, glossopharyngeal and vagal lobes of the carp

A large number of somatostatin (SRIF)-containing structures was demonstrated in the vagal and glossopharyngeal lobes of the carp by means of the indirect immunofluorescent method. The present study further showed that the facial lobe is devoid of these structures. These facts indicate that SRIF may have an important role in relaying viscerosensory information from the vagal and glossopharyngeal nerve but not from the facial nerve.