Synapses forms

Fig. 2 Electron micrograph of synapses. The image shows synapses formed by cultured cortical neurons from mouse. Note abundant synaptic vesicles in nerve terminals adjacent to synaptic junctions that are composed of presynaptic active zones and postsynaptic densities (open arrows point to postsynaptic densities of synaptic junctions synapse on the right contains two junctions). In addition to synaptic vesicles, two of the nerve terminals contain LDCVs (closed arrows). Calibration bar = 500 nm. (Image courtesy of Dr. Xinran Liu, UT Southwestern).

The synaptology of dopaminergic axons in the striatum also exhibits other striking and complex features (Sesack, 2003). These axons release DA at symmetric synapses formed by varicosities (Fig. 18B), acting on the DA receptors within or closely adjacent to the synapse. Some of the synaptically released DA diffuses away from the synaptic cleft, exerting parasynaptic actions on DA receptors located at a distance from the synapse. 

Hersch et al. (1995) found that D1 immunoreactive terminals presynaptic to symmetrical synapses were exceedingly rare whereas the D2 immunoreactive terminals were quite frequent. Synapses formed by D2 immunoreactive terminals were not easy to identify due to a lack of pronounced pre or postsynaptic densities, but many D2 positive presynaptic terminals made symmetrical synapses with dendritic shafts and spines. Consistent with this, many presynaptic D2 receptors were also seen in terminals which were not positive for TH, suggesting they may be heteroreceptors (Sesack et al., 1994). This is confirmed by the demonstration of the D2 positive GABA axon terminals presynaptic to symmetrical synapses (Delle Donne et al., 1997). 

Neuromuscular junctions are the synapses formed between motor neurones and muscle cells. They always use the neurotransmitter acetylcholine and are always excitatory. Motor neurones also form specialised synapses with secretory cells. 

Revy P, Sospedra M, Barbour B,Trautmann A Functional antigen-independent synapses formed between cells and dendritic cells. Nat Immunol 2001 2 925-31. 

Maxwell DJ, Kerr R, Jankowska E, Riddell JS (1997) Synaptic connections of dorsal horn group II spinal interneurons synapses formed with the interneurons and by their axon collaterals. J Comp Neurol 380 51 -69. 

Hamori J, Szentagothai J. (1968) Identification of synapses formed in the cerebellar cortex by Purkinje axon collaterals An electron microscope study. Exp. Brain Res., 5, 118-128. 

A second less frequent type of synapse forms asymmetric synapses along all portions of the dendrites of pallidal neurons. These inputs have been demonstrated, using anterograde tracing with PHA-L, to arise from the subthalamic nucleus (Kita and Kitai 1987). 

In vertebrates, most of the central neurons are neither cholinergic nor cholino-ceptive. In the spinal cord only the synapses formed by the collaterals of the motoneuron axons on the Renshaw cells have proved to be cholinergic. These synapses are part of the self-inhibitory system of motoneurons. Each impulse being pro-... 

Prophase I - the replicated chromosomes condense and pair with homologues in a process called synapsis. This forms a tetrad. Crossing over, the exchange of genetic material between homologues to further increase diversity, occurs during prophase I. 

Bishop, D. K. (1994). RecA homologs Dmcl and Rad51 interact to form multiple nuclear complexes prior to meiotic chromosome synapsis. Cell (Cambridge, Mass.) 79, 1081-1092. 

Group Three The mutation demonstrated dependence upon its homolog. These mutant bands formed puffs in heterozygous combinations when synapsis or asynapsis took place (Aschburner, 1970a, b). 

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