Synaptosomes brain

Wells GB, Lopez MC, Tanaka JC. (1999). The effects of ibogaine on dopamine and serotonin transport in rat brain synaptosomes. Brain Res Bull. 48(6) 641-7. 

Onali P, Olianas MC, Bunse B (1988) Evidence that adenosine A2 and dopamine autoreceptors antagonistically regulate tyrosine hydroxylase activity in rat striatal synaptosomes. Brain Res 456 302-309. 

Terrian, DM., Conner-Kerr, T.A., Privette, T.H., and Gannon, R.L. 1991. Domoic acid enhances the K( + )-evoked release of endogenous glutamate from guinea pig hippocampal mossy fiber synaptosomes. Brain Res 551, 303-307. 

Whalley, C.E., Shih, T.M. (1989). Effects of soman and sarin on high affinity choline uptake by rat brain synaptosomes. Brain Res. Bull. 22 853-8. 

Since P-endorphin is located within the hypothalamus and the pituitary, and has a relatively longer duration of action, it tends to be viewed as a neurohormone. Enkephalins, on the other hand, are more extensively distributed, are very rapidly degraded, and are primarily located in synaptosomal areas. The additional observation that enkephalin release following depolarization of brain (and intestinal) tissues is calcium dependent makes it more realistic to categorize them as neurotransmitters or modulators of synaptic function. Binding sites (receptors) for opioids are found, particularly in synaptosomal brain fractions. The enkephalins are located in neurons whose distribution correlates well with that of the receptors. In fact, regional distribution of peptides and their receptors are closely parallel, as would be predicted for a neurotransmitter system. 

Figure 4. Binding was measured in rat brain synaptosomes using a rapid centrifugation technique. Total ( ), and nonspecific ( ) binding of tritiated PbTx-3 were measured, their difference representing specific binding (A). Rosenthal analysis yields a of 2.6 nM and a B of 6.0 pmol toxin bound/mg protein.

Figure 5. Comparison of specific displacement of 10 nM tritiated saxitoxin (A) or 10 nM tritiated PbTx-3 ( ) by unlabeled competitor saxitoxin or brevetoxin, respectively, in rat brain synaptosomes. IC q in each case is 5-10 nM.

Several brevetoxins have been examined for their respective abilities to competitively displace tritiated brevetoxin PbTx-3 from its specific site of action in brain synaptosomes. Analysis of IC q values revealed no marked differences in the displacing abilities between any of the type-1 toxins, and similarly there was no apparent difference between displacing abilities of PbTx-1 or -7, both type-2 toxins. Although some specific details require correlation, a gross comparison indicates that sodium channels in brain are similar in the systems examined. In the system studied most extensively, the rat brain synaptosome, t-test analysis revealed no significant differences between PbTx-2 and PbTx-3 IC q, or between PbTx-1 and PbTx-7 IC q, but statistically significant differences were found between the two classes (P<0.01) (5). If the Cheng-Prusoff equation (15) is applied ... 

Figure 6. Effect of brevetoxins on tritiated PbTx-3 binding to rat brain synaptosomes. Incubations, in the presence of 50 fig synaptosomal protein and 16 nM tritiated PbTx-3 with increasing amounts of unlabeled PbTx-1 ( ), PbTx-2 ( ), PbTx-3 ( ), PbTx-5 (A), PbTx-6 ( ), or PbTx-7 (o) were for 1 hr at 4 C. Each point represents the mean of three triplicate determinations.

Synaptosomes are pinched-ofP nerve terminals which become severed from the parent axon during gentle homogenisation of brain tissue and then subsequently reseal. They... 

Much evidence supports this scheme. For example, neuronal depolarisation increases the amount of free synapsin in the cytosol and microinjection of CAM kinase II into the terminals of the squid giant axon or brain synaptosomes increases depolarisation-evoked transmitter release. By contrast, injection of dephosphorylated synapsin I into either the squid giant axon or goldfish Mauthner neurons inhibits transmitter release. 

ATP certainly fulfils the criteria for a NT. It is mostly synthesised by mitochondrial oxidative phosphorylation using glucose taken up by the nerve terminal. Much of that ATP is, of course, required to help maintain Na+/K+ ATPase activity and the resting membrane potential as well as a Ca +ATPase, protein kinases and the vesicular binding and release of various NTs. But that leaves some for release as a NT. This has been shown in many peripheral tissues and organs with sympathetic and parasympathetic innervation as well as in brain slices, synaptosomes and from in vivo studies with microdialysis and the cortical cup. There is also evidence that in sympathetically innervated tissue some extracellular ATP originates from the activated postsynaptic cell. While most of the released ATP comes from vesicles containing other NTs, some... 

Richelson, E and Pfenning, M (1984) Blockade by antidepressants and related compounds of biogenic amine uptake into rat brain synaptosomes most antidepressants selectively block noradrenaline uptake. Eur. J. Pharmacol. 104 277-286. 

It could not be anticipated that the extension of the alpha-methyl of MDMA to an alpha-ethyl would also attenuate the effects of the compound on dopaminergic pathways in the brain. In contrast to MDMA, MBDB has no significant effect either on inhibition of uptake of dopamine into striatal synaptosomes (Steele et al. 1987) or on release of dopamine from caudate... 

A variety of side-chain modified analogs of MDMA and MBDB have begun to be examined. Very early studies were of the a,a-dimethyl analog, 3,4-methylenedioxyphentermine (figure 8a) and its N-methyl derivative (figure 10). This latter compound proved to lack MDMA-like activity (Shulgin, unpublished). Interestingly, this compound also lacked the ability to stimulate the release of [ H] serotonin from prelabeled rat brain synaptosomes (Nichols et al. 1982). 

G.K.W. Effects of certain hallucinogenie amphetamine analogs on the release of [ H]serotonin from rat brain synaptosomes. J Med Chem 25 530-535, 1982. 

Steele, T.D. Nichols, D.E. and Yim, G.K.W. Stereochemical effects of 3,4-methylenedioxymethamphetamine (MDMA) and related amphetamine derivatives on inhibition of uptake of [ H]-monoamines into synaptosomes from different regions of rat brain. Biochem Pharmacol 36 2297-2303, 1987. 

Knapp, S. Mandell, A.J. and Geyer, M.A. Effects of amphetamines on regional tryptophan hydroxylase aetivity and synaptosomal conversion of tryptophan to 5-hydroxytryptamine in rat brain. J Pharmacol Exp Ther 189 676-689, 1974. 

Preliminary experiments to delineate the optimum conditions for [ H]MDA and [ HJMDMA binding to rat brain membranes indicated that the best signal-to-noise ratio was found using a crude synaptosomal preparation incubated at 4 °C. While most experiments employed 50 mM Tris-HCl (pH 7.1) as the incubation medium, we found that the addition of 0.27 M sucrose to the incubation medium increased the specific binding approximately fivefold. Subsequent experiments were carried out under both conditions. Other preliminary experiments suggested that [ H]MDA and... 

H]MDMA interacted with multiple sites in rat brain. A low affinity pH]MDA binding site (apparent Kd>1.0 mM) was found to be resistant to boiling of the synaptosomal preparation for 15 minutes. This site was saturable, as indicated by a 30 pereent inhibition of [ H]MDA binding to boiled synaptosomes by 1.0 mM MDA and a 56 pereent inhibition of the binding by 0.1 mM of the serotonin uptake bloeker paroxetine. The indication of a saturable, nonspecific binding site for [ H]MDA in boiled membranes necessitated that we use boiled tissue to assess nonspecific binding in all subsequent experiments. 

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