Neurotrophin-3 mRNA expression in rat intrafusal muscle fibres after denervation and reinnervation

We have studied the regulation of the expression of neurotrophin-3 (NT-3) mRNA in neonatal and adult rat muscle spindles after denervation and after denervation followed by reinnervation. Denervation of the intrafusal fibres did not result in an upregulation of the NT-3 mRNA expression but decreased this expression below the detection limit of the in situ hybridization method. Reinnervation of intrafusal fibres restored the NT-3 mRNA expression. The results suggest that the expression of NT-3 mRNA in postnatal muscle spindles is controlled by neuronal factors. The intrafusal fibre derived NT-3 may act as an instructive, feedback messenger for innervating neurons and may play a role in stabilizing and maintaining functional neuromuscular connections. (C) 1997 Elsevier Science Ireland Ltd

Survival and neurite formation of mesencephalic trigeminal neurones of the rat in vitro

In order to study the development and functional properties of single, isolated, rat mesencephalic trigeminal neurones, a cell-culture procedure was developed for these specific primary sensory neurones. Mesencephalic trigeminal neurones were isolated from the brainstem of 16-day-old rat embryos. Various factors thought to promote the survival and growth of these neurones in vitro were examined. Outgrowth and maintenance of mesencephalic trigeminal neurones in vitro appeared to be stimulated by a muscle-derived factor, present in muscle-conditioned medium or in muscle extract. Of the neurotrophic factors examined, brain-derived neurotrophic factor and neurotrophin-3, but not nerve-growth factor, promoted the survival of rat mesencephalic trigeminal neurones. Optimal survival of these neurones was found to occur on a monolayer of astrocytes, an effect mediated through direct cell-to-cell interactions

Immunogold localization of serotonin within synaptic terminals in the rat mesencephalic trigeminal nucleus

With the use of postembedding electron-microscopic immunogold cytochemistry, the vesicular distribution of serotonin within serotonergic synaptic terminals in the mesencephalic trigeminal nucleus was determined in order to obtain further insight into the mechanisms and function, significance of serotonin release to these jaw muscle spindle afferent neurons, Immunogold labelling was restricted to the previously described type I and type Il terminals. The distribution of immunogold particles over the synaptic terminals indicated that serotonin was stored in small round or pleomorphic (RSV) vesicles and in large granular dense-cored (DSV) vesicles. The amount of serotonin present in the DSV vesicles, which are generally considered to contain colocalized neuropeptides, showed a high degree of variation. These DSV vesicles were usually located at some distance from the synaptic area of the terminals suggesting that they represent a nondirectly releasable vesicle pool. The serotonergic RSV vesicles were,in general, irregularly distributed over the terminals, However, in about 19% of the analyzed labelled synaptic terminals serotonergic RSV vesicles were clustered together near their release site at the synaptic cleft. These synaptic terminals may represent highly active serotonergic synapses with a high release frequency and a high reuptake level, resulting in a dense concentration of vesicles containing a high amount of serotonin neat the synaptic cleft

SELECTIVE EXPRESSION OF NEUROTROPHIN-3 MESSENGER-RNA IN MUSCLE-SPINDLES OF THE RAT

The expression of neurotrophin-3 messenger RNA was studied by in situ hybridization in rat muscle spindles from the first embryonic stages of their formation until their mature appearance in adult animals. The first expression of neurotrophin-3 messenger RNA in developing muscles was observed at E19 in the firstly formed intrafusal fiber, the nuclear bag2 fiber. High levels of neurotrophin messenger RNA were found in the equatorial region of these intrafusal fibers in thin lines of cytoplasma around and between the packed-up nuclei. From E21 on, neurotrophin-3 messenger RNA was also present in the nuclear bag1 type intrafusal fiber. The expression of neurotrophin-3 messenger RNA in nuclear chain fibers, which were found in muscle spindles from day 6 after birth, was low and insignificant in comparison to the expression in the nuclear bag fibers. After completion of muscle spindle formation around the third week after birth, high levels of neurotrophin-3 messenger RNA remained present in the intrafusal fibers throughout life. During the entire period of muscle formation, examined from E15 on, as well as in mature muscles, no neurotrophin-3 messenger RNA could be detected in extrafusal fibers by in situ hybridization. The exclusive intramuscular expression of neurotrophin-3 messenger RNA in intrafusal fibers during development as well as in mature stages suggests the involvement of neurotrophin-3 in the formation and the maintenance of muscle spindles

Ultrastructural localisation of intramuscular expression of BDNF mRNA by silver-gold intensified non-radioactive in situ hybridisation

A non-radioactive in situ hybridisation method is described for the detection of low intramuscular levels of brain-derived neurotrophic factor (BDNF) mRNA at the electron microscope level. Application of high-grade silver-gold intensification of the diaminobenzidine end product of in situ hybridisation revealed that in adult rat muscle the constitutive expression of muscular BDNF is confined to the myofibres; satellite cells, Schwann cells, endothelial cells, fibroblasts or axons do not appear to contribute to BDNF production in normal muscle. Although muscular BDNF is a neurotrophic factor for innervating motoneurons and supposedly released only at the motor endplates, the production of BDNF mRNA appears to occur along the entire length of the myofibres and is not confined to nuclei in the postsynaptic regions

CYCLIC-NUCLEOTIDES AND GROWTH-REGULATION OF THE MANDIBULAR CONDYLAR CARTILAGE OF THE RAT INVITRO

By exogenous interference in the intracellular level of cAMP and cGMP during growth in vitro without and with compression, an indication was obtained for the mediatorial involvement of these cyclic nucleotides in the major growth-processes in the mandibular condylar cartilage of 4-day-old rats. Raising the intracellular level of cAMP reduced proliferative activity in the prechondroblast zone, did not affect matrix synthesis by the functional chondroblasts and stimulated the process of hypertrophy. Intracellular elevation of cGMP had an antagonistic effect; it stimulated proliferation as well as matrix synthesis, but had no effect on hypertrophy. In this specific type of cartilage, cGMP can be considered as a major secondary intracellular messenger for proliferation-stimulating continuous biomechanical stimuli