Stereotaxic injection of tetanus toxin in rat central nervous system causes alteration in normal levels of monoamines

Monoclonal antibodies against a dopamine-releasing protein (DARP) arrest fetal development, decrease brain catecholamines, and increase adrenal weight of neonatal rats

Monoclonal antibodies (MAb) were produced against a partially purified dopamine-releasing protein (DARP) to examine the feasible physiological role of this factor during the development of the rat. These IgM isotype MAbs, and not other IgM antibodies (controls), induced a remarkable increase in fetal resorption and stillbirth rate and impaired the developmental increase of catecholamine concentration in the corpus striatum and hypothalamus of newborn rats. Neonatal injections of the anti-DARP MAb (a single injection of 200 mug, 24 h after birth or 40 mug on alternate days during the first 10 days) decreased the dopamine (DA) concentration of the corpus striatum by 30% on Day 10 and 15% on Day 25 and drastically impaired (by 43% on Day 25) the developmental increase in hypothalamic DA. Furthermore, in the hypothalamus, there was a marked decrease in epinephrine and an increase in norepinephrine (NE) concentration, suggesting an impairment in PNMT function. Neonatal anti-DARP injections also resulted in increased adrenal weight (45 and 44% on Days 10 and 25, respectively) and elevated NE content (anti-DARP, 315 +/- 12 ng, vs control, 223 +/- 16 ng, n = 6). Intrafetal injection of anti-DARP MAb (40 mug) on E 17 resulted in increased resorption and stillbirth accounting for 83% fetal loss. A 10-mug dose of the antibody produced 33% of fetal resorption or stillborn fetuses, whereas control injections resulted in only 4.4% of fetal loss. These data strongly suggest that DARP may be a neurotrophic factor involved in the growth and differentiation of central catecholaminergic neurons and probably necessary for the maturation of PNMT during the early development of rat brain.

Gliosis in the mouse hippocampus without neuronal death after systemic administration of high dosage of tetanus toxin

Tetanus toxin (TeT), an exotoxin, has been studied to cause tetanus in mammalian brains, and it can block the release of some neurotransmitters and affect seizure propagation. In the present study, we investigated neuronal damage/death and glial changes in the mouse hippocampus after systemic administration (intraperitoneal injection) of TeT 10 and 100 ng/kg. In both the 10 and 100 ng/kg TeT-treated groups, no neuronal death occurred in any subregions of the mouse hippocampus until 24 h post-treatment; however, there were changes in glia in the hippocampus depending on time course and dosage. The morphology of GFAP-immunoreactive astrocytes and Iba-1-immunoreactive microglia was apparently changed in the 100 ng/kg TeT treated-group compared to the 10 ng/kg TeT treated-group. In the 100 ng/kg TeT treated-group, they were increased in size and their immunoreactivity was distinctively increased from 12 h post-treatment. We also found that their protein levels were increased in the hippocampus at 12 h post-treatment of 100 ng/kg TeT. In conclusion, these results indicate that the systemic administration of 100 ng/kg TeT induced a distinctive microglia changes in the mouse hippocampus without any neuronal death/damage.

Evidence for different exocytosis pathways in dendritic and terminal dopamine release in vivo

Although dendritic release was first proposed in the 1970s, the mechanism of release is still subject to debate. We have used in vivo microdialysis to study the acute effects of botulinum toxin A, B and tetanus toxin injected in the substantia nigra or striatum of freely moving rats. Spontaneous and evoked dopamine release decreased in both regions after treatment with the SNAP-25 (synaptosome-associated protein of 25 kDa) cleaving protease botulinum toxin A (1000 mouse lethal doses, MLD). Tetanus toxin (4000 MLD) did not significantly change spontaneous or evoked dopamine release in striatum or in the substantia nigra. Another synaptobrevin cleaving protease, botulinum toxin B, inhibited release in the striatum by 55% but did not affect dopamine release when injected in the substantia nigra. The results indicate that both terminal and somatodendritic dopamine release need intact SNAP-25 to occur, but somatodendritic dopamine release in contrast to terminal release depends on a botulinum toxin B resistant pathway.

Central serotonin system in Dystonia musculorum mutant mice: biochemical, autoradiographic and immunocytochemical data

The autosomal recessive mutation dystonia musculorum (dt(J)/dt(J)) causes degenerative alterations of peripheral and central sensory pathways that lead to ataxia. To investigate possible changes in the central serotonin system of these mice, HPLC measurements of 5-hydroxytryptophan, 5-hydroxy-tryptamine (serotonin; 5-HT), and 5-HT metabolites were obtained from 22 brain regions and the spinal cord of wild type and dt(J)/dt(J) mutant mice. Also, 5-HT transporters were quantified by [(3)H]citalopram autoradiography in 72 brain regions, subregions, and nuclei, and the 5-HT innervation visualized by immunocytochemistry throughout the brain and spinal cord. In all brain regions measured for indoleamine content, there were no significant differences between the two genotypes. In the spinal cord, an increased tissue concentration of 5-HT (+34%), 5-hydroxyindole-3-acetic acid (+33%), 5-hydroxytryptophol (+21%), and 5-hydroxytryptophan (+45%) in dt(J)/dt(J) actually corresponded to the same total amount of each of these indoleamines in the entire spinal cord, when taking into account its reduced size in the mutants. Quantification of the binding to 5-HT transporters showed increases in the medial geniculate nucleus (+14%), medial (+24%) and lateral (+18%) hypothalamus, interpeduncular (+13%), vestibular (+22%), and deep cerebellar nuclei (+37%) of dt(J)/dt mice, and decreases in the ventral tegmental area (-13%), median and linear raphe nuclei (-20%), as well as in the solitary complex (-35%). There were no apparent differences in the distribution of 5-HT-immunostained fibers in these and other regions of brain and in the spinal cord of dt(J)/dt(J) compared to wild type mice. The bulk of these results indicates a relative sparing of the central 5-HT system in the dt(J)/dt(J) mice, even though alterations in 5-HT transporters could justify attempts at improving the sensorimotor dysfunction by administration of serotoninergic agents in these mice.

Clostridium neurotoxins influence serotonin uptake and release differently in rat brain synaptosomes

Clostridium neurotoxins produce inhibition of both basal and K(+)-evoked serotonin release in rat brain synaptosomes. To produce these effects, tetanus toxin (TeTx), as well as botulinum neurotoxin type A (BoNT/A), added to brain synaptosomes, must be incubated at 37 degrees C over a long interval (hours). This serotonin exocytosis inhibition was abolished with previous treatment with specific Zn2(+)-metalloprotease inhibitors. Nevertheless, a short incubation time produces different behavior of the indicated neurotoxins: TeTx significantly blocks the sodium-dependent, high-affinity serotonin uptake, whereas a small increase of this uptake was found with BoNT/A. Both Zn2(+)-metalloprotease active fragments, light chains of TeTx and BoNT/A, are unable to reproduce the block of the serotonin uptake, whereas the C-terminal portion of the TeTx heavy chain (Hc-TeTx), which binds specifically to the target tissue, inhibited the serotonin uptake in a dose-dependent manner. The IC50 of Hc-TeTx ranges from 0.62 to 2.08 nM. Binding of [3H]imipramine and [3H]serotonin did not change after toxin treatments, which indicates that these clostridium neurotoxins do not act on the serotonin high-affinity site at the serotonin transporter or at other serotonin high-affinity sites. These results could indicate that TeTx and Hc-TeTx bind to different targets than BoNT/A in the plasma membrane.

Inhibition by tetanus toxin of sodium-dependent, high-affinity [3H]5-hydroxytryptamine uptake in rat synaptosomes

Tetanus toxin (TeTx) is a powerful clostridial neurotoxin that inhibits Ca2+-dependent neurotransmitter secretion as do the botulinum neurotoxins (BoNTs). We found that TeTx (but not BoNT/A) produced a specific time- and dose-dependent inhibition of Na+-dependent [3H]5-hydroxytryptamine (serotonin, 5-HT) uptake in rat CNS synaptosomes. This effect was found in all CNS tryptaminergic areas, being maximal in the hippocampus and occipital cortex. TeTx produced the maximum reduction in [3H]5-HT uptake after 30 min of preincubation, being significant also at lower doses (10(-12) M) or shorter incubation times (10 min). Serotonin transport inhibitors such as fenfluramine (IC50, 11.0 +/- 0.9 microM), paroxetine (IC50, 33.5 +/- 0.1 microM), and imipramine (IC50, 89.9 +/- 5.7 microM) were 3 or 4 orders of magnitude less potent than TeTx (IC50, 8.7 +/- 1.0 nM). Of the two fragments of TeTx, (the C-terminal portion of the neurotoxin heavy chain, which is responsible for the binding to the nerve tissue) was consistently more effective than the L-H(N) fragment (the light neurotoxin chain disulfide linked to the N-terminal portion of the heavy chain, which is responsible for the toxic metalloprotease action) as inhibitor of [3H]5-HT uptake in synaptosomal preparations (56 +/- 5% and 95 +/- 3% with respect to control, respectively). Antagonism of the toxin-induced [3H]5-HT uptake blockade could not be reversed by zinc chelators but did have the ability to antagonize the TeTx inhibition of basal and K+-evoked [3H]5-HT release in rat synaptosomes. The reduction in serotonin accumulation induced by TeTx could be responsible for some tetanic symptoms that have been related to the serotonergic system.

Effect of tetanus toxin on basal and evoked release of 5-hydroxytryptamine and dopamine in rat hippocampus in vivo

Tetanus toxin is a potent neurotoxin which produces seizures and usually death in mammals. In the present study, we have investigated the effect of tetanus toxin on extracellular basal and evoked release of 5-hydroxytryptamine (5-HT), dopamine (DA) and their metabolites in vivo, 7 days after toxin injection into the hippocampus of rats. Tetanus toxin decreased both basal and evoked release of 5-HT and DA. The 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) was not significantly decreased in the extracellular space. Of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) concentration was decreased while that of homovanillic acid (HVA) was unchanged. These findings are considered in light of the possible contributory role that a decrease in monoamine concentration in the hippocampus might have in the effects of tetanus toxin.

Tetanus toxin inhibits depolarization-induced [3H]serotonin release from rat brain cortex synaptosomes

The effects of tetanus toxin on depolarization-induced [3H]serotonin release from superfused rat brain cortex synaptosomes was investigated. Two hours' preincubation of the synaptosomes with tetanus toxin resulted in a concentration-dependent decrease of K(+)-stimulated release, with an IC50 of about 30 nM (4.5 micrograms/ml); this inhibitory effect was blocked by a previous incubation of the tetanus toxin with antitoxin serum. Tetanus toxin had no effect on reserpine-induced release, a model of Ca(2+)-independent release. These results indicate that tetanus toxin is able to alter the exocytotic machinery of serotoninergic terminals, in agreement with results obtained with other neurotransmitters. They also indicate that serotoninergic terminals possess the receptor for tetanus toxin. These findings are in line with in vivo observations suggesting a role for serotoninergic system in tetanus intoxication.

Tetanus toxin alters 5-hydroxytryptamine, dopamine, and their metabolites in rat hippocampus measured by in vivo microdialysis

Tetanus toxin is a potent neurotoxin, the mode of action of which is unknown, although it is widely considered to be mediated by loss of inhibitory neurotransmission. In the present study we have investigated the effect of a single unilateral injection of tetanus toxin in the hippocampus on extracellular concentrations of 5-hydroxytryptamine (5-HT), dopamine and their metabolites in freely moving rats. Tetanus toxin treatment caused a progressive decline in hippocampal dialysate 5-hydroxytryptamine over the 3-day period following the injection. After 3 days the level of 5-HT on the injected side was only 20% of the control side. On the second day of observation the level of dopamine was found to be elevated by more than 2-fold but this was not the case for either of the other 2 days studied. The 5-hydroxytryptamine metabolite, 5-hydroxyindoleacetic acid declined in a manner similar to that of the parent transmitter, but to a lesser extent. Of the dopamine metabolites, 3,4-dihydroxyphenylacetic acid was decreased on the second and third days of observation, whilst homovanillic acid was not significantly altered during the period of observation.