Synapses number

Historically, varicosities have been thought to be the site of synaptic contact of dopamine axons in the striatum. The points of actual synaptic contact are so small that they are difficult to detect in a single thin electron microscopy (EM) sections serial sections are needed and synaptic specializations may only be present in one section. Studies using the serial EM have revealed that varicosities are not preferentially involved in synaptic contacts (Pickel et al., 1982 Freund et al., 1984 Groves et al., 1994). Counts of varicosities, therefore, do not necessarily reflect the dopamine synapse numbers it is necessary to use dopamine specific labels, such as antibodies to tyrosine hydroxylase (TH) or transporter-specific markers, such as 5-hydroxy-dopamine (5-OHDA) together with serial EM. 

What is renovating in your brain right now as you are learning about signaling of memory formation, a fraction of which you vdll perhaps retain in your memory for years to come The answer is neuronal plasticity, the key prelude to memory formation. It is a consequence of both, qualitative alteration in efficacy of synaptic transmission and quantitative alteration in synapse number due to synaptic growth. 

Is dendritic arborization and synapse number important for variability in cognitive ability (Anderson Donaldson 1995) Zagon has reported that postnatal administration of naltrexone, an opiate receptor antagonist, augments rat brain size and increases cortical neuron dendritic arborization (Hauser et al 1989, Zagon McLaughlin 1984). In MAM-treated rats, I showed that postnatal treatment with naltrexone could ameliorate the behavioural deficit for attention to novelty, habituation performance and response flexibility (see Fig. 5) with intermediate effects on time to perform a reasoning task. 

Barbosa AC et al (2008) MEF2C, a transcription factor that facilitates learning and memory by negative regulation of synapse numbers and function. Proc Natl Acad Sci USA 105(27) 9391-9396... 

Rett syndrome Decreased synapse number, reduced number of spines, and elevated LlNEl retrotransposon mobility [97]... 

Geinisman, Y., and Bondareff, W., 1976, Decrease in the number of synapsis in senescent brain a quantitative electron microscopic analysis of the dentate gyrus molecular layer in the rat, Mech. Ageing Dev. 5 11-23. 

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