THE OBSERVATIONS ON 5-HT-, SP-, AND LENK-LIKE IMMUNOREACTIVE ULTRASTRUCTURES OF THE VENTROLATERAL SUBDIVISION OF MIDBRAIN PERIAQUEDUCTAL GRAY IN THE RAT / 解剖学报

ABSTRACT

5-HT-, SP- and L-ENK-like (5-HT-LI, SP-LI and L-ENK-LI) immunoreactive ultrastructures of the ventrolateral subdivision (VLS) of midbrain periaqueductal gray (PAG) in the rat were observed by immunoelectron microscopical technique in the present study. 5-HT-LI neuronal cell bodies were frequently seen in the VLS of the PAG. 5-HT-LI dendrites were found to form axo-dendritic synapses with non-immunoreactive axon terminals, and the major form of this kind of synapse was asymmetric. A few 5-HT-LI axon terminals formed axo-axonic synapses with non-5-HT-LI axon boutons. 5-HT-LI and non-5-HT-LI axon boutons formed axo-dendritic and axo-somatic synapses with 5-HT-LI dendrites, non-5-HT dendrites and 5-HT-LI neuronal cell bodies, respectively. SP-LI fusiform neuronal cell bodies were only a few and formed axo-somatic synapses with non-SP-LI synaptic boutons which contained pleomorphic vesicles. SP-LI dendrites formed axo-dendritic synapses with non-SP-LI axon terminals, this kind of synapse was the main form of synapses formed by SP-LI structures. SP-LI axon boutons formed axo-somatic and axo-dendritic synapses with non-SP-LI neuronal cell bodies and SP-LI dendrites. L-ENK-LI neuronal cell bodies were also limited. The most common form of synapses of L-ENK-LI structures was L-ENK-LI dendrites formed axo-dendritic synapses with non-L-ENK axon terminals. Non-L-ENK-LI axon terminals constituted axo-somatic synapses with L-ENK-LI neuronal cell bodies. A few L-ENK-LI axon terminals formedaxo-dendritic synapses with L-ENK-LI dendrites. The majority of the synapses mentioned above contained spherical clear vesicles, but some were mixed with a few flat, oval and granular vesicles. The immunoreacrive products were located on the surface of vesicles or on the surface of membranous organelles in the cytoplasm.