Guillermo Jaim-Etcheverry

DSP-4: a novel compound with neurotoxic effects on noradrenergic neurons of adult and developing rats.

The pharmacological actions of the compound N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4) are compatible with a specific neurotoxic effect on both peripheral and central noradrenergic neurons. The systemic injection of DSP-4 to adult rats transiently alters sympathetic neurons in the periphery but in the central nervous system the compound determines a marked and prolonged reduction of noradrenaline (NA) levels in all brain regions studied. When DSP-4 was injected systemically to rats at birth in doses ranging from 6.25 to 100 micrograms/g, no changes were found in peripheral sympathetic neurons 40 days later. On the contrary, in the same conditions and in relation to the dose injected, there were marked and persistent changes in the levels of NA in different regions of the brain. In the cerebral cortex and the spinal cord, the neonatal injection of SDP-4 produced a marked and long-lasting depletion of NA levels, similar to that observed after injection of the compound to adult rats. These changes were accompanied by a moderate increase in brain stem NA and a marked elevation of the amine in the cerebellum. These changes, different from the depletion observed in both regions when the compound was given to adult rats, are however similar to those observed after the neonatal injection of the neurotoxic compounds 6-hydroxydopamine or its precursor amino acid, 6-hydroxydopa. This indicates that probably central noradrenergic neurons respond in the same manner after different chemical injuries. DSP-4 crosses the placental barrier because when it was given to pregnant rats at the end of gestation, long-term changes were found in brain NA levels in their offspring, similar to those produced by the neonatal administration of the compound. This new neurotoxic compound provides a very useful tool for the study of noradrenergic neurons both in adult animals and during ontogenesis.

Neurotoxicity of N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP 4) on noradrenergic neurons is mimicked by its cyclic aziridinium derivative

Abstract The haloalkylamine N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP 4), impairs the ability of central and peripheral noradrenergic neurons to take up exogenous noradrenaline (NA) and produces a long-lasting reduction of endogenous NA levels. Previous work has shown that DSP 4 apparently binds to the NA carrier system where it is cyclized spontaneously to an aziridinium compound that seems to trigger the degenerative changes responsible for NA depletion as a result of the alkylation and irreversible inactivation of the carrier. To establish the importance of the binding of unchanged DSP 4 for the production of these changes, the compound was injected immediately after dissolving it or after its incubation under conditions known to favor its conversion into the aziridium derivative. Endogenous NA levels were studied in the brain and heart of adult mice. DSP 4, given immediately after being dissolved, depleted heart and brain NA. When injected after being incubated, DSP 4 reduced NA levels in the periphery but not in the central nervous system. This failure was due to the inability of the aziridinium ion to pass the blood-brain barrier because it could deplete NA when given directly into the brain. Pretreatment with the uptake blocker desmethylimipramine counteracted the effects of both DSP 4 and the aziridinium derivative. Thus, fixation of DSP 4 to the carrier is not a prerequisite for the activity of the aziridinium derivative as the derivative can interact directly with the membrane NA uptake system of central and peripheral noradrenergic neurons to produce the changes characteristic of DSP 4 administration.

Regional differences in the long-term effect of neonatal 6-hydroxydopa treatment on rat brain noradrenaline

Abstract 6-Hydroxydopa (6-OH-DOPA), the precursor amino acid in the biosynthesis of 6-hydroxydopamine, traverses the blood-brain barrier and determines a permanent alteration of central adrenergic neurons after its systemic administration. When the drug is injected into newborn rats, it produces a long-lasting depletion of whole brain noradrenaline (NA). However, if different brain regions are separated for study, a marked and persistent increase in brain stem NA is observed, while in the tele-diencephalon the content of the amine is strongly reduced. A similar effect is observed in the offspring of rats injected with 6-OH-DOPA during gestation. These results most probably reflect either the impaired growth or the destruction of adrenergic nerve terminals in the forebrain as well as the accumulation of NA in preterminal axons, anomalous sprouts or cell bodies in the brain stem region.

6-hydroxydopa during development of central adrenergic neurons produces different long-term changes in rat brain noradrenaline.

6-hydroxydopa (6-OH-DOPA) administered to rats during their early development produces long-term modifications in the content of brain noradrenaline (NA) which have regional differences. An increase in brain stem NA is observed when the rats are exposed to the drug between the day 14 of gestation and the 9th postnatal day. When 6-OH-DOPA is injected subcutaneously on the 13th postnatal day or later, there is a decrease in brain stem NA. On the other hand, the content of NA in the telediencephalon is depleted for the first time in rats exposed to the drug during the day 16 of gestation, the decrease is more evident when the injection is done on days 17 or 18 and the effect is also marked when the drug is administered in the period between the day of birth and the 20th day of age. These results indicate that 6-OH-DOPA exerts different effects during the process of development and that the increase in brain stem NA is not solely dependent on the depletion produced in the forebrain because both phenomena are temporally dissociated. The adrenergic neurons injured by the drug, most probably respond in such a way that leads to an increase in brain stem NA only during the period in which they are under the influence of the factors controlling their physiologic development.

Permanent depletion of peripheral norepinephrine in rats treated at birth with 6-hydroxydopamine.

The injection of 6-hydroxydopamine to newborn rats causes the destruction of neurons in the sympathetic ganglia of the pre- and paravertebral chains and a long lasting reduction of norepinephrine in sympathetically innervated tissues and of their capacity to retain 3H-norepinephrine. A permanent partial sympathectomy is thus achieved since no recovery is observed 3 or 5 months after administration of the drug.

Stimulation-depletion of serotonin and noradrenaline from vesicles of sympathetic nerves in the pineal gland of the rat

SummaryThe pineal gland of the rat receives a rich nervous supply originating from the superior cervical ganglia. These fibers contain serotonin in addition to their neurotransmitter, noradrenaline. Cytochemical studies at the ultrastructural level have shown that both amines are present in the cores of the granular vesicles that are characteristic of these nerves. It is presently shown that the bilateral electrical stimulation of the preganglionic fibers innervating the ganglia markedly reduces the number of small sites reacting cytochemically for both noradrenaline and serotonin, these sites corresponding to the cores of small granular vesicles, while the larger reactive sites (cores of large vesicles) remain unaltered. The vesicles are retained in nerve terminals after stimulation, as observed in conventionally processed tissues, although with altered sizes and shapes. Apart from these cytochemical and structural changes, nerve stimulation also reduces the endogenous noradrenaline content of the pineal gland. Thus, both noradrenaline and serotonin are released from their storage sites in pineal sympathetic nerves after electrical stimulation in vivo. This suggests the possibility that several substances with presumed transmitter or modulatory functions might be simultaneously released by nerve impulses from a given nerve terminal.

Different alterations in the development of the noradrenergic innervation of the cerebellum and the brain stem produced by neonatal 6-hydroxydopa

Abstract The administration of 6-hydroxydopa (6-OH-DOPA) to rats during their pre- or postnatal development, produced long-term modifications in the distribution of noradrenaline (NA) within the brain. In the cerebellum, the concentration of NA was increased in adult rats exposed to the drug between the day 16 of gestation and the day of birth. When injected 3 days after birth, the drug did not modify NA levels while treatment at 20 days produced a marked depletion of cerebellar NA. The concentration of NA in the brain stem showed a different pattern of response to 6-OH-DOPA. Prenatal administration elevated NA in this region and, in contrast to the response of the cerebellum, injections in the inmediate postnatal period also elevated the transmitter content. Treatment at 20 days after birth resulted in a marked depletion of NA levels in the adult brain stem. These results demonstrate the existence of temporal differences in the responses to neonatal 6-OH-DOPA in two structures innervated by noradrenergic pathways originated in neurons of the nucleus locus coeruleus.

6-Hydroxydopamine during development: Relation between opposite regional changes in brain noradrenaline☆

Abstract The perinatal injection of the neurotoxic compounds 6-hydroxydopamine and 6-hydroxydopa, persistently alters the ontogenesis of central noradrenergic neurons in rats, i.e. there is a long-lasting elevation of noradrenaline (NA) in the brain stem and the cerebellum and a reduction in the cortex and spinal cord NA. The latter has been interpreted as due to the destruction of NA-containing terminals while the increase of NA in the brain stem seems to result from a neuronal outgrowth thought to be the response to forebrain denervation. To study the importance of this process for the increase of brain stem NA, various doses of 6-hydroxydopamine were given intraventricularly at birth. Small amounts of the compound (12.5–50 μg) produced the expected effects but 75 μg, while similarly depleting cortical and spinal NA, failed to increase NA levels in the brain stem and the cerebellum. This dissociation could be due to the fact that the high dose of 6-hydroxydopamine altered the noradrenergic neurons to such an extent as to prevent their sprouting when stimulated by the denervation. However, the systematic injection of 6-hydroxydopa given at 3 days of age, increased brain stem NA to a comparable extent in non-treated rats and in those that received 75 μg of 6-hydroxydopamine at birth. These results suggest that forebrain denervation is not the sole stimulus responsible for triggering the processes leading to the increase of NA in the brain stem.

Ultrastructural evidence for monoamine uptake by vesicles of pineal sympathetic nerves immediately after their stimulation

SummaryBilateral electrical stimulation of the preganglionic fibers to the superior cervical ganglia of the rat markedly reduces the number of osmiophilic dense cores present in the nerve vesicles of the sympathetic fibers in the pineal gland. These cores owe their density to the presence of noradrenaline and serotonin in the vesicles. When sympathetic nerves of the pineal organ are exposed immediately after stimulation for a brief period to the false neurotransmitter 5-hydroxydopamine, either in vitro or in vivo, dense precipitates reappear in the electron-lucent vesicles. On the basis of these observations, it is concluded that the vesicles remaining in the nerves after releasing their neurotransmitter content have the capacity to take up and store monoamines. This provides a morphological correlate for the recent biochemical evidence suggesting that the vesicles in sympathetic nerves are reused after neurotransmitter release.

Differential effect of various 6-hydroxydopa treatments on the development of central and peripheral noradrenergic neurons

Abstract 6-Hydroxydopamine or 6-hydroxydopa injected systematically into newborn rats produced marked changes in the development of central and peripheral noradrenergic neurons. Noradrenaline concentration was elevated in the brain stem, particulary in the pons, and decreased in the cerebral cortex and the spinal cord while in the cerebellum, the effects were dependent on the mode of administration. The changes produced by 6-hydroxydopa in brain regional noradrenaline were related to the dose injected at birth. Similar modifications in the development of central noradrenergic neurons were found in the offspring of rats which had received 6-hydroxydopa at 16 days of gestation. The involvement of peripheral sympathetic neurons varied with the compound used and the form of its administration. Thus, 6-hydroxydopamine produced a permanent although partial peripheral sympathectomy, an effect which was less evident following multiple injections of 6-hydroxydopa after birth and almost minimal after a single injection. The prenatal administration of 6-hydroxydopa did not alter peripheral sympathetic neurons. It is concluded that with the appropriate treatment schedule, it is possible to lesion selectively the noradrenergic neurons in the central nervous system.