Selective depletion of spinal noradrenaline abolishes post-decapitation convulsions

Previous data have suggested that spinal noradrenaline (NA) might be important in the normal expression of post-decapitation convulsions. This hypothesis was tested by selective depletion of spinal NA through stereotaxic infusions of 6-hydroxydopamine into the medulla in adult rats. This treatment was found to substantially reduce spinal NA and to abolish the post-decapitation convulsions. The results are discussed in terms of the mechanism underlying the involvement of NA in this reflex.     

The effect of 5,6-dihydroxytryptamine on post-decapitation convulsions

Previous data (1) have shown that L-DOPA increases the duration of the clonic phase of post-decapitation convulsions (PDC) in mice. It was suggested that this effect is produced by depleting 5-hydroxytryptamine (5-HT) in the inhibitory bulbospinal pathways and thus enhancing reflex activity in the spinal cord. If this were true then L-DOPA administration should not influence clonic PDC in animals whose 5-HT pathways were destroyed. We therefore tested the effects of L-DOPA on mice 3 weeks after pretreatment with the 5-HT neurotoxin, 5,6-dihydroxytryptamine (5, 6-DHT) (50 μg/kg, intracerebroventricularly). All mice were given the peripheral decarboxylase inhibitor, Ro 4-4602. 5,6-DHT halved the brain 5-HT levels and significantly increased the duration of clonic PDC. The administration of L-DOPA (320 mg/kg i.p.) to 5,6 DHT treated mice did not produce any further significant increases in duration. The administration of 5-hydroxytryptophan (5-HTP) (100 mg/kg, i.v.) to 5,6-DHT treated mice, however, increased 5-HT to above control levels and reduced convulsions to control levels. Administration of both 5-HTP and L-DOPA to 5,6-DHT treated mice resulted in 5-HT levels and convulsion times which were also not significantly different from the controls. These data give additional indication that intact 5-HT nerve terminals are necessary for L-DOPA to prolong the duration of clonic PDC.     

Postictal behavioral arrest in the rat: “catalepsy” or “catatonia”?

A period of immobility following chemically (picrotoxin, metrazol) or electrically-activated (maximal electroshock) convulsions was demonstrated to possess features of neuroleptic-type catalepsy. During postictal immobility rats had vivid righting and corneal reflexes and responded t to the tail-oinch. Like haloperidol-pretreated animals they were able to remain on the vertical grid or horizontal bar for 15–60 sec or longer. Ten-fifteen minutes after seizure when catalepsy was minimal or not detectable, animals became totally unresponsive to pressure applied to the tail (“delayed analgesia”). Systematically administered haloperidol (0.25–2 mg/kg) did not affect postictal catalepsy while naloxone (5–10 mg/kg) and apomorphine (10 mg/kg) reduced the duration of the immobility period. Unlike naloxone, apomorphine diminished the intensity of cataleptic behavior. Higher doses of naloxone (20–70 mg/kg) when injected during the postictal period induced violent convulsions. None of the two drugs antagonized delayed analgesia.Daily administration of electroshock caused a build up of postictal rigidity and analgesia, coexisting with symptoms of catalepsy. Naloxone antagonised rigidity but failed to interfere with catalepsy and analgesia.     

The behavioural effects of systemically administered kainic acid: A pharmacological analysis

Systemic injection of kainic acid (KA), a powerful neuroexcitant and structural analogue of glutamate, induced a complex behaviour in the rat characterized by early “wet-dog-shakes” (WDS and delayed convulsions. 1) The WDS syndrome was antagonized by serotonin blockers (mianserin and cyproheptadine) and by GABAmimetic agents, which decrease serotonergic transmission; in contrast, WDS were potentiated by compounds which enhance serotonin-mediated events (fluoxetine, fenfluramine, imipramine and tranylcypromine) as well as by blockade of GABA receptors (bicuculline). In addition, WDS were antagonized by haloperidol (which possesses some anti-serotonin properties) whereas KA potentiated haloperidol-induced catalepsy, an effect which was blocked by cyproheptadine. This suggests that KA induces WDS and potentiates catalepsy via an increase in serotoninergic function. 2) KA induced convulsions were antagonized by GABAmimetic agents, in agreement with their broad anticonvulsant spectrum; in contrast, mianserine and cyproheptadine did not affect or even potentiated seizures. Thus KA seizures respond differently to pharmacological treatment than do WDS, and may me related to the nwuro-excitatory action of KA.     

Acute action of DSP-4 on central norepinephrine axons: biochemical and immunohistochemical evidence for differential effects

Previous immunohistochemical studies of the long-term effects of the noradrenergic neurotoxin DSP-4 have demonstrated a remarkably selective vulnerability of norepinephrine (NE) axons of the locus coeruleus (LC). NE axons originating in non-LC NE neurons appear to be largely resistant to the neurotoxic action of DSP-4. We conducted this study to evaluate the acute effects of DSP-4 on NE axons in four different brain regions: cerebral cortex, cerebellum, ventral forebrain, and hypothalamus. NE levels were determined by high-performance liquid chromatography (HPLC) 6 and 24 hr and 14 days after DSP-4 administration. NE axons in these brain regions were visualized in brain sections at 6 and 24 hr after drug treatment, using a specific antiserum to NE. HPLC assays revealed profound reductions of NE levels in cerebral cortex and cerebellum, but only minor decreases in ventral forebrain and hypothalamus. NE immunohistochemistry showed dramatic differences in the acute effects of DSP-4 on NE axon staining: nearly complete loss of staining in cortex and cerebellum, in contrast to an almost unchanged staining pattern in ventral forebrain and hypothalamus. This study demonstrates that NE immunohistochemistry is a valuable tool to assess the acute effects of DSP-4 on NE axons in different brain regions. The results provide the first direct evidence that NE axons are not uniformly acted on by DSP-4 and suggest that the acute effects of DSP-4 are restricted to LC axons.     

Nisoxetine prevents the 6-hydroxydopamine induced decrease in post-decapitation convulsions

Intraventricular injection of 6-hydroxydopamine (60HDA) to rats caused a marked reduction in post-decapitation convulsions (PDC), which was also observed in rats given 60HDA systemically at birth. The reduction in PDC and norepinephrine (NE) content in brain and spinal cord was completely prevented by pretreatment with the selective norepinephrine uptake inhibitor, nisoxetine, but not by fluoxetine, a specific serotonin uptake inhibitor. Presumably nisoxetine prevented the reduction in PDC and NE levels by blocking the entry of 60HDA into the neuron via the membrane uptake pump, and thus preventing subsequent NE depletion and neuron degeneration. These data imply that NE neurons are involved in the neurological mechanism of PDC, although this does not exclude a role for other neurotransmitters such as serotonin (5HT) and dopamine (DA).     

Electroencephalographic study of the effect of neurotoxin DSP-4 in iron model of chronic focal epilepsy.

The effect of the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) on electroencephalographic activity (EEG) was studied in the model of chronic focal epilepsy induced by intracortical injection of FeCl3 in the rat. EEG activity was recorded from the epileptogenic focus (ipsilateral and contralateral) in chronic experiments before and after DSP-4 treatment. In some experiments EEG activity was also simultaneously recorded from the cortical epileptogenic focus and locus coeruleus before and after DSP-4 treatment to study the effect of iron-induced seizure activity and of DSP-4 on the locus coeruleus electrical activity. The results showed that DSP-4 aggravated the iron-induced epileptiform activity as well as the locus-coeruleus electrical activity. The data also showed that, induction of epilepsy by FeCl3 is accompanied by enhancement of the locus coeruleus electrical activity. Our study demonstrates that DSP-4 intensifies and modifies the epileptic activity in the iron-induced chronic epilepsy model and that the effects of toxin persist for a longer duration.     

Effects of Pretreatment with N-(2-Chloroethyl)-N-Ethyl-2-Bromobenzylamine (DSP-4) on Methamphetamine Pharmacokinetics and Striatal Dopamine Losses

Abstract : We recently demonstrated that pretreatment with N -(2-chloroethyl)- N -ethyl-2-bromobenzylamine (DSP-4) exacerbates experimental parkinsonism induced by methamphetamine. The mechanism responsible for this effect remains to be elucidated. In this study, we investigated whether the exacerbation of chronic dopamine loss in DSP-4-pretreated animals is due to an impairment in the recovery of dopamine levels once the neurotoxic insult is generated or to an increased efficacy of the effects induced by methamphetamine. We administered different doses of methamphetamine either to DSP-4-pretreated or to intact Swiss-Webster mice and evaluated the methamphetamine-induced striatal dopamine loss at early and prolonged intervals. As a further step, we evaluated the striatal pharmacokinetics of methamphetamine, together with its early biochemical effects. We found that previous damage to norepinephrine terminals produced by DSP-4 did not modify the recovery of striatal dopamine levels occurring during several weeks after methamphetamine. By contrast, pretreatment with DSP-4 exacerbated early biochemical effects of methamphetamine, which were already detectable 1 h after methamphetamine administration. In addition, in norepinephrine-depleted animals, the clearance of striatal methamphetamine is prolonged, although the striatal concentration peak observed at 1 h is unmodified. These findings, together with the lack of a methamphetamine enhancement when DSP-4 was injected 12 h after methamphetamine administration, suggest that in norepinephrine-depleted animals, a more pronounced acute neuronal sensitivity to methamphetamine occurs.     

Effects of DSP-4 on monoamine and monoamine metabolite levels and on beta adrenoceptor binding kinetics in rat brain at different times after administration

Effects of DSP-4 on noradrenaline (NA), 3-methoxy-4-hydroxyphenyl glycol (MHPG), serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) levels and on beta adrenoceptor binding kinetics (Bmax and K_D) in rat hippocampus, cortex and hypothalamus were studied between 24 hours and 14 days after systemic administration. Beta adrenoceptor numbers in hippocampus and cortex, but not in hypothalamus, were significantly increased after DSP-4. No significant changes in K_D values were observed in hypothalamus, but significant increases in this parameter were measured in hippocampus and cortex. NA and MHPG levels were significantly decreased in all three brain regions, but MHPG/NA ratios were increased in hippocampus, decreased in cortex and unchanged in hypothalamus. Very prominent increases in 5-HIAA levels were observed in all three brain regions, but only at one day after DSP-4. The greatest increases in 5-HIAA levels occurred in the hippocampus, but this effect of DPS-4 appeared to be slightly diminished by pre-treatment with fluoxetine. In cortex and hippocampus 5-HT levels were slightly, but significantly decreased after DSP-4.     

Differential effects of DSP-4 administration on regional brain norepinephrine turnover in rats

The effects of DSP-4 on brain NE levels and turnover in rats were investigated in six brain regions: cortex, hippocampus, cerebellum, brainstem, hypothalamus and locus coeruleus. Administration of 50 mg/kg of DSP-4 significantly decreased NE levels in all brain regions; greatest reductions occurred in the cortex (86% decrease) and in the hippocampus (91% decrease). Doses of DSP-4 less than 50 mg/kg did not significantly lower NE levels in other brain regions, except within the cerebellum. Levels of the NE metabolite 3-methoxy, 4-hydroxyphenylethylene glycol sulfate (MHPG-S04) declined in parallel with those of NE, except within the brainstem and the locus coeruleus. NE turnover, expressed as the ratio of the MHPG-S04 concentration to that of NE, was higher in the cortex and hippocampus than other regions in control animals, and NE turnover significantly increased only in these two areas after the administration of 50 mg/kg of DSP-4 (p less than 0.01). There were no significant changes in the levels of dopamine and a significant decrease of serotonin only in the striatum. These results indicate that DSP-4 is a neurotoxin with a strong predilection for noradrenergic neurons, that its effects vary according to brain region and that its administration increases NE turnover in those brain regions showing the greatest depletion of NE.     

Ceruletide, ceruletide analogues and cholecystokinin octapeptide (CCK-8): effects on motor behaviour, hexobarbital-induced sleep and harman-induced convulsions

Ten ceruletide analogues and cholecystokinin octapeptide (CCK-8) were compared with ceruletide regarding neuropharmacological effects in mice after subcutaneous administration. The effects under study were catalepsy, prolongation of hexobarbital-induced sleep and delay in onset of harman-induced convulsions. Ceruletide and several analogues were more potent than the reference drugs, diazepam and haloperidol. Desulfation, deamidation and shortening of the peptide chain by five amino acids strongly reduced or abolished the pharmacological activities of ceruletide. Other chemical modulations mostly weakened the efficacy, but to an unequal extent for the three effects, which altered the pharmacological selectivity.     

Increase in norepinephrine turnover after tyrosine or DL-threo-3,4-dihydroxyphenylserine (DL-threo-DOPS)

The amino acids tyrosine and DL-threo-3,4-dihydroxyphenylserine (DL-threo-DOPS) were compared for their effectiveness in increasing central nervous system norepinephrine (NE) turnover in both saline and DSP-4 pretreated mice. NE was decreased significantly in cortex, hippocampus and cerebellum, and only slightly in hypothalamus and brainstem two weeks after a single intraperitoneal injection of the neurotoxin DSP-4. Levels of the major NE metabolite, 3-methoxyl-4-hydroxyphenylethylene glycol (MHPG), decreased in parallel in these five brain regions. Neither administration of tyrosine (250 mg/kg, as the ethyl ester, i.p.) nor DL-threo-DOPS (200 mg/kg, i.p.) affected regional NE concentration. However, after tyrosine administration, MHPG levels increased significantly in cortex in control mice and in cortex and hippocampus of DSP-4 pretreated mice. In all five brain noradrenergic regions MHPG level increased after DL-threo-DOPS administration and this increase was enhanced (approximately doubled) in DSP-4 pretreated mice. Thus, both amino acids may be useful as precursors of central NE when its level is depleted (e.g. following administration of DSP-4); DL-threo-DOPS producing a generalized increase in brain NE turnover, while increases following tyrosine are specific to those areas in which neuronal activity is increased i.e. cortex and hippocampus.     

Neuropharmacological spectrum of muscimol

Muscimol was tested in comparison with a series of reference compounds in a variety of situations in which GABA-related drugs are known to have an effect. Muscimol blocked the convulsions and/or lethality due to picrotoxinin, strychnine and a low dose of bicuculline. It was inactive against higher dosis of bicuculline, metrazole or electroshock convulsions. Muscimol reduced both the basal and the picrotoxin-induced multi-unit activity of the neurons of the dorsal Deiters' nucleus ; although active at low doses, the maximum effect of muscimol was relatively weak. Muscimol potentiated neuroleptic-induced catalepsy, and this effect was bicuculline sensitive ; it did not induce catalypsy in the presence of sulpiride. At high doses muscimol blocked apomorphine-induced stereotyped behaviour. It is proposed that muscimol is a GABA agonist of high affinity but of relatively low efficacy as based on its spectrum of neuropharmacological activities “in vivo”.     

Pretraining infusion of DSP-4 into the amygdala impaired retention in the inhibitory avoidance task: involvement of norepinephrine but not serotonin in memory facilitation

The present study investigated the involvement of amygdala noradrenergic (NE) and serotonergic (5-HT) systems in memory storage processing. Rats bearing chronic cannulae in the amygdala were trained on a one-trial inhibitory avoidance task and tested for retention 24 hrs later. Five days prior to training, rats received intra-amygdala infusion of vehicle or various doses of N-2-chloroethyl-N-ethyl-2-bromobenzylamine (DSP-4)-a NE-specific neurotoxin when given peripherally. Results showed that pretraining intra-amygdala infusion of 10.0 micrograms or 30.0 micrograms of DSP-4 impaired retention. Further, 30.0 micrograms of DSP-4 also abolished the memory enhancing effect of epinephrine (E) injected peripherally. However, local infusion of DSP-4 depleted not only NE but also 5-HT and DA substantially. Subsequent experiments found that the retention deficit induced by 30.0 micrograms of DSP-4 could be ameliorated by 0.2 microgram NE but not by 5-HT at a wide range of doses infused into the amygdala shortly after training, which ascribed the deficit to depletion of NE. After protecting the 5-HT terminals by a pretreatment of fluoxetine (15.0 mg/kg), pretraining intra-amygdala infusion of 30.0 micrograms DSP-4 shifted the memory-enhancing dose of E from 0.1 mg/kg to 1.0 mg/kg. In contrast, pretraining intra-amygdala infusion of 15.0 micrograms 5,7-dihydroxytryptamine (5,7-DHT) or DSP-4 with a pretreatment of desipramine (DMI, 25.0 mg/kgx2) to protect NE terminals failed to impair retention or attenuate the memory enhancing effect of 0.1 mg/kg E injected peripherally. These findings, taken together, suggest that the memory modulatory effect of peripheral E involved, at least partially, the amygdala NE system.     

Neuroprotective Effects of Some Monoamine Oxidase-B Inhibitors Against DSP-4-Induced Noradrenaline Depletion in the Mouse Hippocampus

Abstract: DSP-4 [ N -(2-chloroethyl)- N -ethyl-2-bromobenzylamine], a selective noradrenaline (NA) uptake blocker, is capable of inducing long-lasting depletion of NA in some noradrenergic axon terminals and of subsequently causing cell death to NA neuronal cell bodies in rodents. R (−)-Deprenyl, a selective monoamine oxidase (MAO)-B inhibitor, has been shown to be capable of protecting animals against this DSP-4-induced neuronal degeneration. Its action, however, has been claimed to be unrelated to the inhibition of MAO-B activity but rather due to competition for the NA uptake sites. The effects of several types of MAO inhibitors against DSP-4 toxicity, MAO-B activity both in vivo and in vitro, and NA uptake into the hippocampus have been assessed. N -(2-Hexyl)- N -methylpropargylamine (2-HxMP), a potent MAO-B inhibitor, for example, exerts no appreciable effect on NA uptake but is quite potent in counteracting the NA-depleting effect of DSP-4. Such results rule out the possibility that the neuroprotective effect of the MAO-B inhibitors is due mainly to their effect on NA uptake. The in vitro inhibition of MAO-B activity seems to correlate positively with their neuroprotective effects against DSP-4. In comparison to the MAO-B inhibitors, NA uptake blockers, such as desipramine and S (+)-deprenyl, exhibit relatively low efficacy in protecting the NA axon terminals from the effects of DSP-4-induced damage. The restoration of hippocampal NA levels is significantly enhanced with repeated treatments of R (−)-deprenyl or 2-HxMP even at very low doses following the DSP-4 insult. This suggests that in addition to neuroprotection, these MAO-B inhibitors may rescue some of the noradrenergic axon terminals damaged by DSP-4.     

Regional Amino Acid Distribution in Relation to Function in Insulin Hypoglycaemia

The amino acids glutamate, aspartate, gamma-aminobutyric acid (GABA), and glutamine were measured as their dansyl derivatives in whole brain and specific brain regions by a sensitive double-labelling technique at various times during the development of hypoglycaemic encephalopathy. Hypoglycaemia was induced by administration of insulin (100 i.u./kg) to 24-h fasted rats. No significant changes in glutamate, GABA, or glutamine were detected in whole brain at any time up to and including the onset of hypoglycaemic convulsions. In cerebral cortex, however, GABA levels were reduced to 65% or normal prior to the appearance of neurological symptoms of hypoglycaemia. Onset of symptoms (severe catalepsy and loss of righting reflex, but before the onset of convulsions) was accompanied by marked decreases of glutamate and glutamine in striatum and hippocampus. These regions, in addition to cerebral cortex, show the greatest vulnerability to hypoglycaemic insult, according to previous anatomical studies. Aspartate levels were significantly increased (p less than 0.01) in the cerebral cortex of convulsing animals, confirming a previous report. No changes were detectable in any of the amino acids studied in medulla-pons at any time during the progression of hypoglycaemia. Cerebral cortex and striatum showed a selective net loss of amino acids (2.2 and 3.5 mumol/g. respectively) prior to the onset of insulin-hypoglycaemic convulsions.     

Nitric Oxide as a Signaling Factor To Upregulate the Death-Specific Protein in a Marine Diatom, Skeletonema costatum, during Blockage of Electron Flow in Photosynthesis

To determine the physiological functions of a novel death-specific protein gene, Skeletonema costatum DSP-1 (ScDSP-1) in a marine diatom, Skeletonema costatum, the mRNA abundance of ScDSP-1 was measured in cultures subjected to light manipulation and treatments with various chemicals. When cells were transferred to a dim light intensity of 15 μmol m⁻² s⁻¹, ScDSP-1 mRNA levels showed a transient increase of 1 to 17.2 μmol (mol 18S rRNA)⁻¹ in 60 h. Furthermore, treatments with the photoinhibitors 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) resulted in high ScDSP-1 mRNA levels, which reached 943 and 72 μmol (mol 18S rRNA)⁻¹, respectively. Treatment with the nitric oxide (NO) donor diethylamine nitric oxide also induced ScDSP-1 expression, and this inducible expression was inhibited by the NO scavenger hemoglobin. Additionally, the expression of ScDSP-1 mRNA elicited by DCMU and DBMIB was efficiently reduced when cultures were pretreated with the cell-penetrating NO scavenger 2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. In contrast, treatment with another photoinhibitor, paraquat, had no effect on ScDSP-1 expression. Our results indicated that NO is the crucial secondary messenger which signals the expression of ScDSP-1 when electron flow between photosystem II and photosystem I is blocked in S. costatum cells. In addition, the discovery of a similar gene, ScDSP-2, is briefly described.     

The role of dopamine and serotonin in the prolongation of post-decapitation convulsions in mice.

L-DOPA (320 mg/kg, i.p.) increased the duration of the clonic phase of post-decapitation convulsions (PDC) by 60% in mice pretreated with the peripheral decarboxylase inhibitor, Ro 4-4602 (50 mg/kg, i.p.). Assays of brains at the time of decapitation showed a 300% increase in dopamine (DM), an 80% reduction in serotonin (5-HT) and no change in norepinephrine (NE) levels. The effect of L-DOPA on PDC was not blocked by haloperidol (0.5 – 5.0 mg/kg), a blocker of DM receptors, nor by diethyldithiocarbamate (400 mg/kg) an inhibitor of NE synthesis. Parachlorophenylalanine (300 mg/kg × 3 days) produced an 80% reduction in 5-HT and a prolongation of PDC similar to that observed after L-DOPA. Prolongation of PDC was also seen after the 5-HT antagonists methysergide (5 mg/kg) and cinanserin (10 mg/kg), but not after cyproheptadine (10 mg/kg). The 5-HT precursor, 5-hydroxytryptophan (100 mg/kg), produced no change in PDC when used alone but inhibited L-DOPA's prolongation of PDC. The results suggest that L-DOPA acts by depleting 5-HT in bulbospinal pathways and thus enhancing reflex activity in the spinal cord.     

Catalepsy induced by morphine or haloperidol: effects of apomorphine and anticholinergic drugs.

To investigate the extent of cholinergic involvement in opiate-induced catalepsy, the effects of three anticholinergic drugs were studied on morphine-induced catalepsy. Haloperidol-induced catalepsy was also examined. Maximum catalepsy in rats was obtained with 30 mg/kg morphine or 3 mg/kg haloperidol. The anticholinergic drugs atropine, benztropine, and scopolamine were unable to antagonize morphine-induced catalepsy, yet readily antagonized haloperidol-induced catalepsy. Low doses of apomorphine (7.5 mg/kg), on the other hand, readily antagonized morphine catalepsy, but 13-fold higher doses of apomorphine were needed to block haloperidol-induced catalepsy. The results are compatible with the idea that catalepsy can be mediated via the striatum or the amygdala; morphine-dopamine antagonism may occur in the amygdala, whereas morphine-dopamine-cholinergic interactions occur in the striatum.     

Monoaminergic Changes in Locus Coeruleus and Dorsal Raphe Nucleus Following Noradrenaline Depletion

The goal of our study was to assess the monoaminergic changes in locus coeruleus (LC) and dorsal raphe nucleus (DRN) following noradrenaline (NA) depletion. Seven days after a single N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) intraperitoneal administration in mice, we observed a decrease of NA in both the LC and DRN, as well as in prefrontal cortex (PFC) and hippocampus (HIPP). Moreover, an increase of serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) was detected at LC level, while no change was found in DRN. DSP-4 also caused a significant decrease of dopamine (DA) tissue content in HIPP and DRN, without affecting the LC and the PFC. A decrease of DA metabolite, homovanillic acid (HVA), was found in the DRN of NA-depleted mice. These results highlight that the neurotoxic action of DSP-4 is not restricted to LC terminal projections but also involves NA depletion at the cell body level, where it is paralleled by adaptive changes in both serotonergic and dopaminergic systems. T. Cassano and S. Gaetani have contributed equally to the present study.