In vitro H-serotonin (5-HT) synthesis and release in BALBc and C57BL mice. II. Cell body areas

"In vitro" 3H-5-HT and 3H-5-HIAA, newly synthesized from 3H-TRP, are measured in the brainstem, the anterior raphe nuclei and the locus coeruleus of C57BL and BALBc mice. As found for the caudate nucleus and the hippocampus, higher synthesis and release are determined in C57BL than in BALBc, for the locus coeruleus and more globally, for the brainstem. But these differences disappear when the study is carried on the raphe dorsalis and the raphe centralis nuclei. Therefore the serotonergic activity could be independently regulated at the level of cell bodies and at those of terminals. However, the 5-HT metabolism of NRD of BALBc mice could be submitted to a specific autoinhibition which could explain a lower 5-HT synthesis and release at the corresponding terminal level, compared to C57BL.     

Endogenous serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) levels in large regions and in discrete brain areas of C57BL and BALBc mice at three times of the day

The serotoninergic system has been analysed in the brainstem and the forebrain of adult C57BL and BALBc mice. Endogenous 5-HT and 5-HIAA levels have also been measured in the different raphe nuclei and in the caudate nucleus and the hippocampus of these strains, using the micropunch technique and the radioenzymatic method (for 5-HT) and a new radioimmunoassay (for 5-HIAA). This investigation was performed at three times of the day: 9:00 hr; 14:00 hr; 20:00 hr to underline the differences between the strains. Most of the time, higher 5-HT and 5-HIAA levels are found in the brainstem and the raphe nuclei of the BALBc strain compared to C57BL. In the forebrain the differences are reversed, except in the caudate nucleus and the hippocampus where the levels of 5-HT are identical in the two strains. Moreover the 5-HIAA/5-HT ratio shows a higher turn-over of the amine in the C57BL strain.     

Developmental variations of brain serotonin, tryptophan, 5-hydroxyindole acetic acid, and noradrenaline and dopamine content in two inbred strains of mice

Endogenous levels of tryptophan (TRP), serotonin (5-HT), 5-hydroxyindol acetic acid (5-HIAA), noradrenaline (NA) and dopamine (DA), were measured in the brain-stem and anterior regions of C57BL and BALBc mice whose ages ranged from 1 day postnatal to 12 weeks. In C57BL mice levels of NA were found to be higher in the brainstem from week 1 onwards (except at week 3), and in the anterior region from week 6 onwards than in BALBc mice. 5-HT levels were found to be higher in C57BL mice from day 1 to week 2 in the brain-stem, and in the anterior region at week 1 and from week 5 onwards, compared to BALBc. The evolution of DA levels in the anterior region shows opposite differences before and after week 3-4. Before week 3 lower levels of DA were found in C57BL mice and the reverse is observed from week 5 onwards. Moreover during the postnatal development, the variation of the different components of the serotoninergic metabolism (TRP, 5-HT, 5-HIAA) is similar to that observed in other species.     

Distribution and quantification of 5-HT nerve cell bodies in the nucleus raphe dorsalis area of C57BL and BALBc mice. Relationship between anatomy and biochemistry

BALBc and C57BL mice have been shown to have a different 5-HT metabolism. The present study compares the number and the distribution of 5-HT cell bodies in the nucleus raphe dorsalis area (B7 + B6) of these strains. By using 5-HT immunohistochemistry, we found a higher number of 5-HT neurons in the most caudal part of NRD (B6) of BALBc mice compared to C57BL. This difference may be correlated with a higher level of endogenous 5-HT, a higher uptake capacity toward exogenous [³H]5-HT, and a lower release of the amine in this same area of BALBc mice compared to C57BL. It could also imply a significant participation of the nerve cell bodies in the regulation of 5-HT transmission inside 5-HT nuclei.     

Effect of acute binge cocaine on levels of extracellular dopamine in the caudate putamen and nucleus accumbens in male C57BL/6J and 129/J mice

Levels of dopamine, both basal and after binge-pattern cocaine administration, were measured in the caudate putamen and nucleus accumbens of C57BL/6J and 129/J mice by in vivo microdialysis. Six-week old males were surgically implanted with a CMA guide cannula into the caudate putamen or nucleus accumbens. After 4 days recovery, dialysis probes were lowered into the caudate putamen or the nucleus accumbens and mice were placed in individual microdialysis chambers. The next morning experiments were carried out on freely moving animals. Experimental animals received 1-day binge cocaine administration (15 mg/kgx3, i.p. at hourly intervals) while control animals received saline in the same pattern. Dialysates were collected every 20 min and dopamine content was determined by HPLC with electrochemical detection. Basal levels of dopamine in the dialysate of the caudate putamen were 4.2+/-0.2 nM in C57BL/6J mice and 5.0+/-0.3 nM in 129/J mice. In the nucleus accumbens, basal levels of dopamine were 0.65+/-0.04 nM in the C57BL/6J mice and 0.75+/-0.03 nM in 129/J mice, with no significant differences between strains in either region. Binge cocaine administration significantly increased mean dopamine levels in the caudate putamen in the C57BL/6J mice (with a 3-h mean of 6.80 nM) and in the 129J mice (9.94 nM). In this region, 129/J mice had significantly higher levels of cocaine-induced dopamine than did C57BL/6J mice. In the nucleus accumbens, administration of cocaine also significantly increased dopamine levels in both strains (1.32 nM in C57BL/6J and 1.43 nM in 129/J), but with no difference between strains.     

Mouse strain differences in locomotor,sensitisation and rewarding effect of heroin; association with alterations in MOP‐r activation and dopamine transporter binding

There is growing agreement that genetic factors play an important role in the risk to develop heroin addiction, and comparisons of heroin addiction vulnerability in inbred strains of mice could provide useful information on the question of individual vulnerability to heroin addiction. This study examined the rewarding and locomotor‐stimulating effects of heroin in male C57BL/6J and DBA/2J mice. Heroin induced locomotion and sensitisation in C57BL/6J but not in DBA/2J mice. C57BL/6J mice developed conditioned place preference (CPP) to the highest doses of heroin, while DBA/2J showed CPP to only the lowest heroin doses, indicating a higher sensitivity of DBA/2J mice to the rewarding properties of heroin vs C57BL/6J mice. In order to investigate the neurobiological substrate underlying some of these differences, the effect of chronic ‘intermittent’ escalating dose heroin administration on the opioid, dopaminergic and stress systems was explored. Twofold higher μ‐opioid receptor (MOP‐r)‐stimulated [³⁵S]GTPγS binding was observed in the nucleus accumbens and caudate of saline‐treated C57BL/6J mice compared with DBA/2J. Heroin decreased MOP‐r density in brain regions of C57BL/6J mice, but not in DBA/2J. A higher density of dopamine transporters (DAT) was observed in nucleus accumbens shell and caudate of heroin‐treated DBA/2J mice compared with heroin‐treated C57BL/6J. There were no effects on D₁ and D₂ binding. Chronic heroin administration decreased corticosterone levels in both strains with no effect of strain. These results suggest that genetic differences in MOP‐r activation and DAT expression may be responsible for individual differences in vulnerability to heroin addiction.     

Distinct patterns of Fos expression induced by systemic amphetamine in the striatal complex of C57BL/6JICo and DBA/2JICo inbred strains of mice

Mice from the inbred strains C57BL/6 and DBA/2 are characterized by striking differences in their behavioral response to addictive drugs. We used Fos expression as a tool to reveal strain differences in the postsynaptic effects of amphetamine (AMPH; 2.5 mg/kg) within the nucleus accumbens (NAc) (core and shell) and the dorsal caudate (dorsomedial and dorsolateral). AMPH stimulated Fos expression in all striatal regions of mice from both strains. However, while C57BL/6 showed a higher Fos response than DBA/2 mice in both NAc shell and core, the opposite was true for the dorsolateral caudate. The effects of AMPH were prevented by D1 blockade in all striatal regions of both strains and mimicked by the D1 agonist, SKF82958 (0.1 mg/kg), in both regions of the caudate and in the NAc shell, but not in the core. Our results suggest that the functional heterogeneity of the striatal complex is under genetic control and that this control may implicate DA transmission and corticostriatal interactions.     

Spatial learning in two inbred strains of mice: genotype-dependent effect of amygdaloid and hippocampal lesions.

Spatial learning performance and maze-running strategies were estimated in two inbred strains of mice, C57BL/6 and DBA/2, submitted to an 8-arm radial maze task. Subsequently the genotype-dependent effect of hippocampus and amygdala on the mastering of this task was examined as a function of the different acquisition model provided by each strain. The results firstly show that unoperated C57BL/6 mice reach a higher level of performance and develop a stronger preference for adjacent arms - 45 degrees angle - turns than unoperated DBA/2 mice. In the high learner C57BL/6 strain, both hippocampal and amygdaloid lesions impair performance and modify maze-running strategies. With practice, however, the difference between amygdala-lesioned mice and controls disappears while that between hippocampus-lesioned mice and controls persists. Conversely, in the low learner DBA/2 strain, hippocampal lesions have a negative effect on a single parameter of performance, while amygdaloid lesions only affect maze-running strategies. Taken together, these results confirm the specific control exerted by the hippocampus on spatial learning. Moreover, they suggest that the amygdala can parallel the role of the hippocampus as far as the baseline level of performance of the strain considered is high.     

Comparison of the neuropathological characteristics of bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease (vCJD) in mice

Bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease (vCJD) belong to a group of diseases called the transmissible spongiform encephalopathies (TSEs). Transmission studies in inbred mice (strain typing) provided overwhelming evidence that vCJD arose from BSE. In this study, we compare the patterns of neuropathology in a panel of three inbred mouse strains (RIII, C57BL and VM) and one cross (C57BL x VM) infected with either vCJD or BSE. For each mouse strain, patterns of abnormal prion protein (PrPres) deposition, astrocytosis and vacuolation were similar in the vCJD- and BSE-challenged mice. Prion protein (PrP)-positive plaques were prominent in the VM and C57BL x VM mice in addition to diffuse PrPres accumulation, whereas only diffuse PrPres labelling was observed in the RIII and C57BL mice. The hippocampus was targeted in all mouse strains, as was the cochlear nucleus in the medulla, both showing consistent severe vacuolation and heavy PrPres deposition. Although the targeting of PrPres was similar in the BSE- and vCJD-infected brains, the amount and intensity of PrPres observed in the brains treated with formic acid during fixation was reduced considerably. The distribution of astrocytosis was similar to the targeting of PrPres deposition in the brain, although some differences were observed in the hippocampi of mice challenged with vCJD. We conclude that there are no significant differences in the targeting of neuropathological changes observed in the BSE- and vCJD-infected mice, consistent with the previous evidence of a link between BSE and vCJD.     

Fear conditioning in C57/BL/6 and DBA/2 mice: variability in nucleus accumbens function according to the strain predisposition to show contextual- or cue-based responding

The contribution of the nucleus accumbens shell, the dorsal hippocampus, and the basolateral amygdala to contextual and explicit cue fear conditioning was assessed in C57BL/6 (C57) and DBA/2 (DBA) mice showing differences in processing contextual information associated with consistent but non-pathological variations in hippocampal functionality. Mice from both strains with bilateral ibotenic acid or sham lesions located in each area were introduced in a conditioning chamber and exposed twice to the pairing of a tone (2 x 8 s, 2000 Hz, 80 dB) with a shock (2 s, 0.7 mA). On the following day, mice were first exposed to the training context then to the tone in a different context. Freezing behaviour was scored in all situations. C57 showed more freezing to the context than to the tone whereas DBA showed more freezing to the tone than to the context. In C57, both nucleus accumbens and hippocampal lesions impaired acquisition of contextual fear conditioning but paradoxically improved acquisition of cue fear conditioning, whereas amygdala lesions disrupted performance in every task. In DBA, nucleus accumbens lesions, like amygdala lesions, impaired acquisition of both contextual and cue fear conditioning, whereas hippocampal lesions did not produce any effect. The parallelism between the effect of nucleus accumbens and hippocampus lesions in C57, and between the effect of nucleus accumbens and amygdala lesions in DBA points to a variability in nucleus accumbens function according to the strain specialization to develop context- or cue-based responding.     

Altered 5-HT2A and 5-HT4 postsynaptic receptors and their intracellular signalling systems IP3 and cAMP in brains from depressed violent suicide victims

Serotonin 5-HT2A and 5-HT4 binding parameters and their second messengers 1,4,5-inositol triphosphate (IP3) and cyclic adenosyl monophosphate (cAMP) were studied in the frontal cortex, hippocampus, caudate nucleus and amygdala of 19 control subjects and 19 antidepressant-free, violent suicide victims. A significantly higher number of 5-HT4 receptors and higher second messenger cAMP concentrations were found in the frontal cortex and caudate nucleus of the depressed suicide victims as compared with the control group. Furthermore, significantly increased 5-HT2A binding sites and IP3 concentrations were noted in the caudate nucleus of the suicide victims, together with a significantly reduced number of 5-HT2A binding sites, higher binding affinity and increased IP3 concentrations in the hippocampus. No significant alterations in 5-HT4 and cAMP or in 5-HT2A and IP3 concentrations were observed in the amygdala. The caudate nucleus of depressed suicide victims seems to be the brain region with the highest alteration of the serotonergic system, and hence with the most diagnostic sensitivity. Further studies on suicidality and depression should focus on the functionality of the caudate nucleus.     

Seizures can be triggered by stimulating non-cortical structures in the quaking mutant mouse

Mutant Quaking mice (C57BL/6J) display convulsive tonic-clonic seizures that can be either spontaneous or triggered by manipulation of the animal or by auditory stimulation. Several abnormalities have been found (especially in the noradrenergic system) in the brainstem of this mutant strain. We first verified by electrophysiological recording that the cerebral cortex was not involved in the generation or in the development of these fits. Then we showed that tonic-clonic seizures similar to those obtained in the freely moving animal were triggered by low-threshold (LT, 5-50 microA) or high-threshold (HT, 55-150 microA) stimuli performed during head restraint. LT stimuli were mostly efficient in a number of ponto-bulbar and mesencephalic structures, including several reticular nuclei, the locus coeruleus, the nucleus subcoeruleus and the red nucleus, whereas HT stimuli were generally necessary to trigger fits by stimulating the nuclei pontis, the substantia nigra, the central gray area and the cerebellar nuclei. Seizures were also provoked at the diencephalic level with LT stimulation delivered in the medial thalamic area, the nucleus reticularis thalami and some subthalamic regions (zona incerta, H field of Forel). In contrast, no fits were obtained by stimulating the cerebellar cortex and the inferior colliculus, the ventral and lateral groups of thalamic nuclei or the telencephalic regions (hippocampus, amygdala, caudate nucleus, putamen and cerebral cortex), with the exception of the globus pallidus.     

Basal levels and alcohol-induced changes in nociceptin/orphanin FQ, dynorphin, and enkephalin levels in C57BL/6J mice

In order to investigate the involvement of the opioid and nociceptin/orphanin FQ (N/OFQ) system in alcohol drinking behaviour, N/OFQ and the opioid peptides dynorphin B (DYNB) and Met-enkephalin-Arg(6) Phe(7) (MEAP) were examined in the alcohol-preferring C57BL/6J mice. Basal peptide levels were compared in the brain and the pituitary gland with basal levels in the alcohol-avoiding DBA/2J mice. Furthermore, the effects of chronic alcohol self-administration on peptides were studied in the C57BL/6J mice. Compared to the DBA/2J mice, C57BL/6J mice had low immunoreactive (ir) levels of DYNB and MEAP in the nucleus accumbens, the hippocampus, and the substantia nigra, low ir-DYNB levels in the striatum and low ir-MEAP levels in the frontal cortex. Higher ir-DYNB levels in the pituitary gland and in the periaqueductal gray (PAG) and higher ir-N/OFQ levels in the frontal cortex and in the hippocampus were detected in C57BL/6J mice compared to the DBA/2J mice. After 4 weeks of voluntary alcohol consumption, only minor changes in steady-state peptide levels were identified. However, 5 days after the alcohol-drinking period, lower levels of all peptides were detected in the ventral tegmental area and ir-DYNB levels were also lower in the amygdala and in the substantia nigra. Twenty-one days after cessation of alcohol self-administration, the opioid peptides in alcohol-consuming C57BL/6J mice were lower in the PAG, the N/OFQ was lower in the frontal cortex and DYNB was higher in the amygdala and substantia nigra as compared to control C57BL/6J mice. This study demonstrates strain differences between C57BL/6J mice and DBA/2J mice that could contribute to divergent drug-taking behaviour, and it also demonstrates time- and structure-specific changes in neuropeptide levels after alcohol self-administration in the C57BL/6J mice.     

Genetic studies of daily variations of first-step enzymes of monoamines metabolism in the brain of inbred strains of mice and hybrids. I. Daily variations of tryptophan hydroxylase activity in the nuclei raphe dorsalis, raphe centralis and in the striatum

A daily variation of tryptophan hydroxylase (TrH) activity was observed in the raphe dorsalis (RD), raphe centralis (RC) and striatum (St) of 3 inbred strains of mice (BALB/c, C57BL/6, C57BR) and of the reciprocal hybrids obtained from Balb/c and C57BL6. Significant differences of the characteristics of these rhythms have been found in the same strain between different structures and for the same structure between different strains. In RD and RC hybridization led to less defined daily variations which, in the striatum, remained well synchronized and could be controlled by a dominant genetic mechanism part. These results help to discuss evidence for selective control mechanisms of regulation responsible for daily variation of TrH in the 5-HT cell bodies and terminals and their relative independence.     

Acute 'binge' cocaine administration elevates dynorphin mRNA in the caudate putamen of C57BL/6J but not 129/J mice

Preprodynorphin mRNA was measured in the nucleus accumbens (NAc) and caudate putamen (CPu) after 3-day 'binge' pattern cocaine administration in C57BL/6J and 129/J mice, strains which differ in behavior and in dopamine increases in the CPu after 'binge' cocaine. In the CPu, there was increased preprodynorphin mRNA in C57BL/6J (P<0.05), but not in 129/J mice, with no differences in the NAc. Thus, 129/J mice are hyporesponsive to the preprodynorphin activating effects of acute 'binge' cocaine in the CPu.     

Increased c-Fos protein in the brains of scrapie-infected SAMP8, SAMR1, AKR and C57BL mice

Scrapie is a neurodegenerative disease that occurs naturally in sheep and goats. The histopathological changes include vacuolation, neuronal apoptosis and astrocytosis. The mechanisms involved in neuronal apoptosis are still unknown. Recently, we observed that activated p38 immunohistostaining was increased in scrapie-infected mice. In many neurodegenerative diseases, activation of the p38 pathway and of the immediate-early gene termed c-Fos appears to be required for the initiation of apoptosis. There are similarities in histopathological changes seen in scrapie-infected mice and in an uninfected senescence-accelerated mouse strain (SAMP8). This led us to investigate c-Fos protein levels in the brains of both uninfected and scrapie-infected SAMP8, SAMR1, AKR and C57BL mice using immunohistochemical methods. The SAMR1 strain served as a control in that it is a mouse strain that does not show accelerated ageing, but has a background that is similar to the SAMP8 strain. AKR was used because it is one of the progenitor strains of both SAM strains and, finally, C57BL is a completely unrelated strain. The results showed a low basal c-Fos expression in controls and a marked increase in c-Fos staining in scrapie-infected mice. In scrapie-positive mice, c-Fos immunoreactivity was observed in neurones in the cortex, hippocampus, thalamus, hypothalamus, medulla, midbrain, brainstem, paraterminal body, internal capsule and cerebellar Purkinje cells. Immunoreactivity of c-Fos was also observed in astrocytes in many brain areas of scrapie-infected mice, particularly in the hippocampus and cortex. Our results show that normal mouse brain (NMB)-injected AKR and SAMP8 mice had more c-Fos production than NMB-injected SAMR1 or C57BL mice; scrapie-infection induces significant increases in c-Fos immunoreactivity in all four mouse strains. Our study suggests that the increase in c-Fos levels may play a role in the neuronal apoptosis observed in scrapie-infected mice.     

Proton magnetic resonance spectroscopic imaging of the brain in childhood autism.

BACKGROUND: Autism is a developmental disorder of unknown neurologic basis. Based on prior work, we used proton magnetic resonance spectroscopic imaging ((1)H- MRSI) to investigate brain structures, including cingulate and caudate, that we hypothesized would reveal metabolic abnormalities in subjects with autism. METHODS: In 22 children with autism, 5 to 16 years old, and 20 age-matched healthy control subjects, (1)H-MRSI assessed levels of N-acetyl compounds (NAA), choline compounds (Cho), and creatine plus phosphocreatine (Cr) at 272 msec echo-time and 1.5 T. RESULTS: In subjects with autism compared with control subjects, Cho was 27.2% lower in left inferior anterior cingulate and 19.1% higher in the head of the right caudate nucleus; Cr was 21.1% higher in the head of the right caudate nucleus, but lower in the body of the left caudate nucleus (17.9%) and right occipital cortex (16.6%). CONCLUSIONS: Results are consistent with altered membrane metabolism, altered energetic metabolism, or both in the left anterior cingulate gyrus, both caudate nuclei, and right occipital cortex in subjects with autism compared with control subjects.     

Neuroanatomy and psychomimetic-induced locomotion in C57BL/6J and 129/X1SvJ mice exposed to developmental vitamin D deficiency

Evidence from epidemiology suggests that developmental vitamin D (DVD) deficiency is associated with an increased risk of schizophrenia. DVD deficiency in rats is associated with altered brain morphology and enhanced hyperlocomotion in response to MK-801 and amphetamine. The aim of this study was to determine if similar phenotypes were associated with DVD deficiency in two strains of mice (C57BL/6J, 129/X1SvJ). Brains from neonatal (P0) and adult (P70) mice were imaged using MRI and the volumes of the cerebrum, hippocampus, striatum, septum, cortex and ventricles measured, as well as the widths of white matter tracts. Locomotor sensitivity to 5mg/kg d-amphetamine, 0.5mg/kg MK-801 or saline was examined in a separate group of mice in an open field. DVD deficiency altered brain morphology in C57BL6/J mice, such that C57BL/6J female DVD-deficient neonatal mice had a smaller hippocampus compared to female controls. In addition, adult C57BL/6J male DVD-deficient mice had smaller lateral ventricles compared to controls, which may have been compressed by the enlarged striatum seen in these DVD-deficient mice. However, in contrast to the behavioural phenotypes found in DVD-deficient rats, there was no significant effect of maternal diet on amphetamine or MK-801-induced locomotion in either strain. These data indicate that not only species, but also strain of mouse, moderates the impact of DVD deficiency on neuroanatomical and behavioural phenotypes in rodent animal models.     

Effect of chronic "binge cocaine" on basal levels and cocaine-induced increases of dopamine in the caudate putamen and nucleus accumbens of C57BL/6J and 129/J mice

In vivo microdialysis was used to measure the effect of chronic "binge" pattern cocaine administration on basal and cocaine-induced dopamine levels in the caudate putamen and nucleus accumbens of C57BL/6J and 129/J mice. Mice were implanted with a guide cannula in the caudate putamen or nucleus accumbens and after 4 days recovery, one group received "binge" pattern cocaine administration for 13 days (15 mg/kg x 3, i.p. at hourly intervals) while another group received saline in the same pattern. On the day before microdialysis, dialysis probes were lowered into the caudate putamen and nucleus accumbens. The next morning, after baseline dopamine collection, all animals received "binge" cocaine administration. Dialysates were collected every 20 min and dopamine content was determined by HPLC with electrochemical detection. In the basal condition, the mean level of dopamine in the dialysate from both brain regions of mice pretreated with "binge" pattern cocaine administration was significantly lower than that of the mice pretreated with saline administration. The absolute levels of dopamine achieved following "binge" pattern cocaine challenge were lower in the mice that had received chronic cocaine administration. However, when expressed as percent increase over baseline, the dopamine response to cocaine in the nucleus accumbens was significantly higher in mice that received chronic than in mice that received acute cocaine administration. Chronic cocaine administration led to a lowering of both basal dopamine and the absolute levels of cocaine-induced increases of dopamine in the two brain regions, but enhanced the percent increases over the baseline in response to cocaine in the nucleus accumbens of both mouse strains.