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Synaptogenesis is the formation of synapses between neurons in the nervous system. Although it occurs throughout a healthy person's lifespan , an explosion of synapse formation occurs during early brain development , known as exuberant synaptogenesis . [ 1 ]
The synaptotropic hypothesis, also called the synaptotrophic hypothesis, is a neurobiological hypothesis of neuronal growth and synapse formation. The hypothesis was first formulated by J.E. Vaughn in 1988, [1] and remains a focus of current research efforts. [2]
Neurons in culture develop synapses that are similar to those that form in vivo, suggesting that synaptogenic signals can function properly in vitro. CNS synaptogenesis studies have focused mainly on glutamatergic synapses. Imaging experiments show that dendrites are highly dynamic during development and often initiate contact with axons.
Synaptogenesis is the formation of a synapse and in this case the Neuromuscular Junction is of interest. In this section, the focus is on the development of the NMJ from the outgrowth of axons during development. [1] As mentioned in the development section, Schwann cell precursors accompany growing axons as they reach their associated muscles.
Rats raised with environmental enrichment have thicker cerebral cortices (3.3–7%) that contain 25% more synapses. [5] [7] This effect of environmental richness upon the brain occurs whether it is experienced immediately following birth, [8] after weaning, [5] [7] [9] or during maturity. [10]
These include LTP, long-term depression (LTD), synaptic elimination, neurogenesis, and synaptogenesis. [3] The mechanisms of activity-dependent plasticity result in membrane depolarization and calcium influx, which in turn trigger cellular changes that affect synaptic connections and gene transcription .
This bi-directional trigger aids in the formation of synapses and is a key component to modifying the neuronal network. Over-expression of either of these proteins causes an increase in synapse forming sites, thus providing evidence that neurexin plays a functional role in synaptogenesis. [8]
The highest rate of synaptogenesis is during the first 3 to 6 days, at the end of which, the kitten's spinal trigeminal nucleus will have nearly half of the axo-axonic synapses present in adult cats. Later, between 16 and 27 days of age, there is another surge of axo-axonic synaptogenesis. [ 34 ]