αCaMKII autophosphorylation controls the establishment of alcohol drinking behavior

The α-Ca(2+)/calmodulin-dependent protein kinase II (αCaMKII) is a crucial enzyme controlling plasticity in the brain. The autophosphorylation of αCaMKII works as a 'molecular memory' for a transient calcium activation, thereby accelerating learning. We investigated the role of αCaMKII autophosphorylation in the establishment of alcohol drinking as an addiction-related behavior in mice. We found that alcohol drinking was initially diminished in αCaMKII autophosphorylation-deficient αCaMKII(T286A) mice, but could be established at wild-type level after repeated withdrawals. The locomotor activating effects of a low-dose alcohol (2 g/kg) were absent in αCaMKII(T286A) mice, whereas the sedating effects of high-dose (3.5 g/kg) were preserved after acute and subchronic administration. The in vivo microdialysis revealed that αCaMKII(T286A) mice showed no dopamine (DA) response in the nucleus accumbens to acute or subchronic alcohol administration, but enhanced serotonin (5-HT) responses in the prefrontal cortex. The attenuated DA response in αCaMKII(T286A) mice was in line with altered c-Fos activation in the ventral tegmental area after acute and subchronic alcohol administration. In order to compare findings in mice with the human condition, we tested 23 single-nucleotide polymorphisms (SNPs) in the CAMK2A gene for their association with alcohol dependence in a population of 1333 male patients with severe alcohol dependence and 939 controls. We found seven significant associations between CAMK2A SNPs and alcohol dependence, one of which in an autophosphorylation-related area of the gene. Together, our data suggest αCaMKII autophosphorylation as a facilitating mechanism in the establishment of alcohol drinking behavior with changing the DA-5-HT balance as a putative mechanism.

Environmental enrichment has no effect on the development of dopaminergic and GABAergic fibers during methylphenidate treatment of early traumatized gerbils

It is widely believed, that environmental factors play a crucial role in the etiology and outcome of psychiatric diseases such as Attention-Deficit/Hyperactivity Disorder (ADHD). A former study from our laboratory has shown that both methylphenidate (MP) and handling have a positive effect on the dopaminergic fiber density in the prefrontal cortex (PFC) of early traumatized gerbils (Meriones unguiculatus). The current study was performed to investigate if enriched environment during MP application has an additional influence on the dopaminergic and GABAergic fiber densities in the PFC and amygdala in this animal model.

Animals received a single early dose of methamphetamine (MA; 50 mg/kg; i.p.) on postnatal day (PD) 14, which is known to cause multiple changes in the subsequent development of several neurotransmitter systems including the dopaminergic systems, and were then treated with oral daily applications of MP (5 mg/kg) from PD30–60. Animals treated this way were either transferred to an enriched environment after weaning (on PD30) or were kept under impoverished rearing conditions.

There was no effect of an enriched environment on the dopaminergic or GABAergic fiber density neither in the PFC nor in the amygdala. With regard to former studies these results underline the particular impact of MP in the treatment of ADHD.

Early preweaning methamphetamine and postweaning rearing conditions interfere with the development of peripheral stress parameters and neural growth factors in gerbils

Adrenal steroid hormones and neuronal growth factors are two interacting systemic factors that mediate the environment's influence on the brain's structure and function. In order to further elucidate their role and relationship in the effects of early stressful experience and isolated rearing (IR), this study measured blood corticosterone titres and relative adrenal weights and assessed nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) concentrations in brain regions of both hemispheres of young adult Mongolian gerbils injected on postnatal day 14 with a single high dose of methamphetamine (MA) or saline and raised after weaning either in an enriched or an impoverished environment. Irrespective of MA challenge, IR decreased corticosterone titres to about half, but increased relative adrenal weights. BDNF concentrations were decreased by IR in saline-injected animals in the left prefrontal and parietal cortices and right entorhinal and hippocampal cortices, and in the subcortical regions of both hemispheres. NGF concentrations were unaltered by IR in saline-injected animals, but increased in MA challenged animals in the entorhinal/hippocampal cortices and subcortical areas of both hemispheres. MA application induced shifts of the lateral asymmetry in NGF contents in prefrontal and entorhinal cortices. The results suggest that an early pharmacological traumatization can set a switch for further brain development, and that growth factor concentrations might possibly be influenced by peripheral stress hormones.

Administration of oral methylphenidate during adolescence prevents suppressive development of dopamine projections into prefrontal cortex and amygdala after an early pharmacological challenge in gerbils

The enduring effects of postweaning subchronic methylphenidate (MP) treatment and/or previous early preweaning methamphetamine (MA) application on dopamine (DA) fiber density were investigated in multiple cortical and subcortical areas of the gerbil brain. The study aimed to explore three questions: (1) is the development of DA fiber innervation in control animals sensitive to a clinically relevant subchronic treatment with MP? (2) Is the development of DA fiber innervation in the forebrain altered by a single early MA challenge? (3) If so, might the subsequent institution of a therapeutically relevant MP application scheme interfere with such early induced alternative developmental trajectories for DA fiber innervation? For this purpose, gerbils pretreated both with saline and MA (50 mg/kg, i.p.) on day 14 received either H(2)O or MP (5 mg/kg) orally on days 30 to 60. On day 90, DA fibers were immunohistochemically detected and quantified. As a result, MP on its own did not have any significant influence on the postnatal development of the DA fiber systems, whereas it prevented a previously MA triggered suppressive development of DA fiber innervation in the prefrontal cortex and amygdala complex (30% less fiber innervation in both areas). Thus, MP prevented previously initiated miswiring of DA fibers from actually being implemented in the gerbil forebrain. During earlier studies, rather complex miswiring has been documented in response to an early preweaning MA challenge. This miswiring was associated with functional deficits resembling some of the symptoms of patients with ADHD. Therefore, morphogenetic properties of MP need further attention.

Association between body weight of newborn rats and density of serotonin transporters in the frontal cortex at adulthood

Persisting alterations in monoaminergic innervation patterns have been observed following various environmental manipulations and neuro-psychopharmacological treatments during fetal or early postnatal life. The present study investigates the question how differences in initial growth conditions at birth might interfere with subsequent development of both serotonergic and noradrenergic innervation in the rat frontal cortex (FC) and brain stem. For this purpose, newborn rat littermates were divided into two groups, a low and a high birth weight group, and the densities of both serotonin (5-HT) and norepinephrine (NE) transporters in the FC and brain stem were analyzed at adulthood. 5-HT transporter density in the FC was significantly higher in the high birth weight group as compared with the low birth weight group. No significant differences were observed between both groups in the density of 5-HT transporters in the brain stem and in the densities of NE transporters in FC and brain stem. It is discussed that differences in birth weight may affect the postnatal development of 5-HT projections to the frontal cortex.

Postnatal maturation of cortical serotonin lateral asymmetry in gerbils is vulnerable to both environmental and pharmacological epigenetic challenges

Long-term effects of postnatal differential rearing conditions and/or early methamphetamine (MA) application on serotonin (5-HT) fibre density were investigated in several cortical areas of both hemispheres of gerbils. The aim of this study was twofold: (1) Is the 5-HT fibre innervation of the cerebral cortex lateralised, and (2) if so, do postnatal environmental conditions and/or an early drug challenge interfere with development of 5-HT cerebral asymmetries? For that purpose, male gerbils were reared either under semi-natural or restricted environmental and social conditions, under both conditions once (on postnatal day 14) being treated with either a single dose of MA (50 mg/kg, i.p.) or saline. On postnatal day 110, 5-HT fibres were immunohistochemically stained and innervation densities quantified in prefrontal cortex, insular cortex, frontal cortex, parietal cortex, and entorhinal cortex. It was found that (1) 5-HT innervation in the cerebral cortex was clearly lateralised; (2) direction and extent of this asymmetry were not uniformly distributed over the different areas investigated; (3) both early methamphetamine challenge and rearing condition differentially interfered with adult 5-HT cerebral asymmetry; (4) combining MA challenge with subsequent restricted rearing tended to reverse the effects of MA on 5-HT cerebral asymmetry in some of the cortical areas investigated; and (5) significant responses in 5-HT cerebral asymmetry only occurred in prefrontal and entorhinal association cortices. The present findings suggest that the ontogenesis of cortical laterality is influenced by epigenetic factors and that disturbances of the postnatal maturation of lateralised functions may be associated with certain psychopathological behaviours.

Epigenetic factors differentially influence postnatal maturation of serotonin (5-HT) innervation in cerebral cortex of gerbils: interaction of rearing conditions and early methamphetamine challenge

The effects of disjunctive environmental deprivation combined with a single methamphetamine (MA) challenge on postnatal maturation of the serotonin (5-HT) innervation pattern in cerebral cortex of gerbils were studied. Gerbils were assigned to either enriched (ER) or impoverished (IR) environmental rearing conditions. On postnatal day 110, 5-HT was immunostained. The 5-HT innervation pattern of the brain was qualitatively evaluated and provided in graphic form. The densities of 5-HT fibres were quantified in areas of prefrontal, insular, frontal, parietal, and entorhinal cortices of the right hemisphere using digital image analysis. The early MA challenge led to an overshoot of the fibre density in medial and orbital prefrontal cortex and entorhinal cortex of ER animals. IR animals mostly resisted MA effects except of a restraint of the innervation of the insular cortex. In comparison to enriched rearing, restricted rearing caused overshoot maturation of 5-HT innervation in insular and entorhinal cortices. The present data provide evidence for a region-specific postnatal vulnerability of the maturing 5-HT innervation, namely in association cortices. In contrast, both sensory and motor cortices showed no significant changes at all. The results are discussed in context with previously presented findings of alterations of the cortical dopamine innervation depending on both epigenetic factors. In conclusion, both experimental variables together give new insight into raphe-cortical plasticity that may contribute to a better understanding of the role of 5-HT fibre systems in structural maturation of the cortex. Postnatal environment may be involved in individual vulnerability of a variety of mental disorders during adolescence and aging.

Differential influence of rearing conditions and methamphetamine on serotonin fibre maturation in the dentate gyrus of gerbils (Meriones unguiculatus)

Environmental experience and drugs are two parameters that affect the maturation of neurotransmitter systems. The influence of impoverished rearing (IR) versus enriched rearing (ER) was compared in conjunction with postnatal methamphetamine (MA) treatment. The densities of immunostained 5-HT fibres were quantified in septal and temporal regions of the hippocampal dentate gyrus (DG) in young adult gerbils. In the IR group, 5-HT fibre densities were significantly increased in the molecular, granular and polymorphic layers of the DG in the temporal plane. After postnatal MA treatment, the 5-HT fibre density in the ER group reached a level equivalent to that of the IR group in nearly all respects. Under IR conditions, the pharmacological intervention significantly increased the maturation of fibre densities in septal layers only in the right hemisphere with no significant alterations in the left hemisphere and in temporal regions of either hemisphere. According to our previous studies on hippocampal neurogenesis, adaptations of 5-HT fibre densities partly proved to be positively correlated to cell proliferation rates for each of the specific conditions. Thus, the induced MA sensitivity, caused by pharmacological intervention at day 14, was manifested as direct interaction of 5-HT fibre maturation and cell proliferation in dependence of environmental factors. Both IR and MA together give us a better understanding of raphe-hippocampal plasticity and offer new perspectives for pharmacological studies on the 5-HT participation in mental disorders.

Postnatal rearing conditions influence ontogeny of adult dopamine transporter (DAT) immunoreactivity of the striatum in gerbils

In the present study, the influence of postnatal rearing conditions on the structural maturation of the striatum of adult male gerbils (Meriones unguiculatus) was investigated. For that purpose, animals were bred and reared either grouped in an object-filled environment (EC) or isolated under restricted environmental conditions (IC). At the age of postnatal day 90, dopamine fibers were stained immunocytochemically using an antibody against the dopamine transporter (DAT). Innervation density was determined along the entire rostrocaudal axis of the ventromedial and dorsolateral part of the striatum. As a result, restricted rearing produced a significant restraint of the maturation of striatal dopamine (DA) innervation, leading to adult fiber densities which were approximately 9% below those in semi-naturally reared gerbils. Results are discussed with structural and functional alterations observed in the brain of IC animals.

A novel pharmacological concept in an animal model of psychosis

OBJECTIVE

We have analysed pharmacologically induced perturbation of functional and structural neurogenesis in the prefrontal cortex (PFC) and hippocampus.

METHOD

Juvenile gerbils received a single dose of methamphetamine (METH, 50 mg/kg, i.p.). In adults the following parameters were quantitatively investigated: prefrontal dopaminergic and GABAergic innervation densities (immunocytochemistry), morphogenesis of pyramidal cells (Golgi), dentate granule cell proliferation (BrdU-labelling), working memory and behavioural inhibition (delayed response, open-field).

RESULT

A single challenge of METH continuously suppresses granule cell proliferation in adult gerbils and initiates rewiring of neuronal networks in the PFC which run concurrently with the development of severe deficits in PFC-related behaviours.

CONCLUSION

It appears that a continuous remodelling of neuronal circuits is an inherent property of the brain, the biological significance of which seems to be to ascertain adaptive interaction between brain and environment. Learning more about drug-induced neuronal reorganization might be basic for understanding the genesis of psychotic conditions in the brain. This presentation is based both on own research and on a review of the literature.

An early methamphetamine challenge suppresses the maturation of dopamine fibres in the nucleus accumbens of gerbils: on the significance of rearing conditions

The effect of a single early methamphetamine (MA) challenge on postnatal maturation of the nucleus accumbens (NAC) was studied. Therefore, male gerbils received a single dose of MA (50 mg/kg, i.p.) on postnatal day 14. At the age of postnatal day 90, dopamine fibres were stained immunocytochemically and innervation density was determined in several test fields along the rostrocaudal extent of both core and shell of the NAC. Since we already know that the differential environment can alter ontogeny of dopamine innervation in the prefrontal cortex of gerbils, in the present study we investigated whether probable drug effects may be influenced by rearing conditions. For that purpose, animals were bred and reared either isolated in standard laboratory cages or grouped in an object-filled environment. The results showed that a single early MA challenge significantly alters maturation of dopamine fibre innervation in both subregions of the NAC. In seminaturally reared gerbils the drug challenge caused dopamine fibre densities which were about 54% below those of saline-treated controls in both the shell and core. However, in animals from restricted rearing this MA-induced effect was more pronounced in the core (-43%) but not significant in the shell (-14%). In conclusion, an early MA challenge caused a significant restraint of adult dopamine fibre density developing in the NAC postnatally. Additionally, rearing conditions significantly interfered with drug-induced alterations in maturation of dopaminergic innervation pattern of the NAC. The present results are discussed with recent findings on MA-induced impairment of prefrontal dopamine innervation and further reactive morphogenetic effects caused by the drug. In this respect, functional interactions between the prefrontal cortex and NAC are specifically considered.

Postnatal maturation of prefrontal pyramidal neurones is sensitive to a single early dose of methamphetamine in gerbils (Meriones unguiculatus)

The effect of a single methamphetamine application on postnatal maturation of the prefrontal cortex was studied using pyramidal cell morphology and spine density as parameters of systemic plasticity. Male gerbils were injected a single dose of methamphetamine (METH, 50mg/kg, i.p.) on postnatal day 14. On postnatal day 90, prefrontal cortices of METH-treated animals and saline-treated controls were processed for Golgi-staining. Dendritic arbours of layer III and V pyramidal neurones were measured to describe pyramidal cell morphology, and segmental spine counts were carried out. The results showed that a single postnatal METH-challenge significantly alters morphological differentiation of pyramidal cells towards adulthood. Cells from METH-treated animals showed a higher total dendritic length based on longer segments between subsequent dendritic branchings, with only the apical stem dendrite being shorter in METH-treated than in control subjects. The branching rate was slightly but not significantly increased in METH-treated animals. Nevertheless, spine density was significantly increased on all types of dendrites, with apical dendrites of both layers III and V showing the highest drug-induced progression of about 50% compared to control values. The present results are discussed with regard to probable clues they may provide for investigating neurobiological principles of psychotic behaviour in an animal model.

Granule cell proliferation and axon terminal degradation in the dentate gyrus of gerbils (Meriones unguiculatus) during maturation, adulthood and aging

The objective of the present study was to examine both naturally occurring degrading events in axon terminals of the dentate gyrus and granule cell proliferation in the dentate gyrus of gerbils (Meriones unguiculatus) throughout postnatal life. For that purpose, (1) a selective silver staining technique was applied to analyze neuronal lysosome accumulation (LA), indicating synaptic degradation during development. LA was quantified by counting silver grains in the inner third and outer two thirds of the molecular layer, granular layer, subgranular layer and the hilus of the dentate gyrus. (2) Proliferation of granule cells was identified by in-vivo labeling with 5-bromo-2'-desoxyuridine (BrdU). BrdU-labeled granule cell nuclei were identified in consecutive horizontal slices along the mid-septotemporal axis of the hippocampus and light-microscopically quantified 4h after the BrdU-labeling. It was found (1) that in young animals LA significantly increased within all layers and reached adult levels after about 3 months. During subsequent development LA kept on this level throughout aging with highest values within the inner molecular layer. (2) There was a highly significant temporal gradient in granule cell proliferation with numbers of BrdU-labeled cells exponentially declining during juvenile life. Nevertheless, granule cell proliferation occurred throughout adult life and aging. The present results are discussed (1) with concepts of ongoing neuroplasticity and remodeling of neuronal networks in the developing and adult brain, and (2) with regard to pharmacologically induced neuromorphogenesis.

Differential environment alters ontogeny of dopamine innervation of the orbital prefrontal cortex in gerbils

In the present study, the influence of postnatal environmental conditions on the structural ontogeny of the orbital prefrontal cortex of adult gerbils (Meriones unguiculatus) was examined. The animals were bred and reared either isolated in standard laboratory cages or grouped in an object-filled environment. At the age of postnatal day 90, dopamine fibers were stained immunocytochemically and innervation density was determined in the orbital prefrontal cortex. By comparison, restricted rearing produced a restraint of the subsequent maturation of orbital prefrontal dopamine innervation, leading to adult fiber densities that were approximately 38% below those in seminaturally reared gerbils. Results are discussed in terms of activity-dependent postnatal maturation of the cortex and adaptive neuroplasticity with regard to previously published data concerning diminished dopamine innervation in the medial prefrontal cortex (Winterfeld et al. [1998]

Adult treatment with methamphetamine transiently decreases dentate granule cell proliferation in the gerbil hippocampus

The objective of the present study was to examine whether acute treatment with the recreational drug methamphetamine influences adult granule cell proliferation in the dentate gyrus of the hippocampus. For that purpose, at the age of postnatal day 90 adult male gerbils (Meriones unguiculatus) received a single dose of either methamphetamine (25 mg/kg; i.p.) or saline. Proliferation of granule cells was identified by in-vivo labeling with 5-bromo-2'-desoxyuridine (BrdU) which was applied either simultaneously with methamphetamine or 36 h after administration of the drug. BrdU-labeled granule cell nuclei were identified in consecutive horizontal slices along the mid-septotemporal axis of the hippocampus and light-microscopically quantified 7 days after the BrdU-labeling. It was found that in both saline- and methamphetamine-treated animals there was a highly significant spatial septotemporal gradient in granule cell proliferation with numbers of BrdU-labeled cells gradually declining from the septal towards the temporal pole. The acute treatment with methamphetamine suppressed granule cell proliferation by about 28% and the septotemporal gradient of mitotic activity became significantly attenuated. It was further found that 36 h after the drug challenge granule cell proliferation rates had been restored almost to the control values along the whole septotemporal axis of the hippocampus. The present results are discussed with regard to (1) pharmacological regulation of neurogenesis in the hippocampus and (2) probable clues they may provide for both understanding the biological correlates of psychotic disorders and evolution of future concepts in neuropharmacological intervention.

A single neonatal dose of methamphetamine suppresses dentate granule cell proliferation in adult gerbils which is restored to control values by acute doses of haloperidol

A single non-invasive dose of methamphetamine (50 mg/kg; i.p.) was administered to neonatal male gerbils (Meriones unguiculatus) aged 14 days. The first objective of the present study was to examine whether this early drug challenge, which has been shown to induce suppressive postnatal maturation of prefrontal dopamine (DA) innervation (Dawirs et al., 1994), interferes with adult granule cell proliferation in the dentate gyrus. Proliferation of granule cells was identified by in-vivo labeling with 5-bromo-2'-desoxyuridine (BrdU). BrdU-labeled granule cell nuclei were identified in consecutive horizontal sections along the mid-septotemporal axis of the hippocampus and light-microscopically quantified 7 days after BrdU-labeling. It was found that a single neonatal dose of methamphetamine was a stimulus strong enough to significantly attenuate adult granule cell proliferation. This effect was clearly lateralized with significant suppression of mitotic activity becoming apparent solely in the left dentate gyrus (-34%). The second objective of the present study was to examine whether acute doses of haloperidol, which have been found to stimulate granule cell proliferation in healthy adult animals (Dawirs et al., 1988), might restore mitotic activity to control values. For that purpose, at the age of postnatal day 90 adult animals which had been challenged with methamphetamine as juveniles received 4 doses of haloperidol (5 mg/kg; i.p.). Proliferation of granule cells was identified by BrdU-labeling. It was found that this neuroleptic treatment acutely restored granule cell proliferation rates to control values. The present results are discussed with regard to (1) factors, regulating mitotic activity in the hippocampus and (2) probable clues they may provide for understanding the neurobiological basis of psychotic behavior.

A new look at embryonic development of the visual system in decapod crustaceans: neuropil formation, neurogenesis, and apoptotic cell death

In recent years, comparing the structure and development of the central nervous system in crustaceans has provided new insights into the phylogenetic relationships of arthropods. Furthermore, the structural evolution of the compound eyes and optic ganglia of adult arthropods has been discussed, but it was not possible to compare the ontogeny of arthropod visual systems, owing to the lack of data on species other than insects. In the present report, we studied the development of the crustacean visual system by examining neurogenesis, neuropil formation, and apoptotic cell death in embryos of the American lobster, Homarus americanus, the spider crab, Hyas araneus, and the caridean shrimp, Palaemonetes argentinus, and compare these processes with those found in insects. Our results on the patterns of stem cell proliferation provide evidence that in decapod crustaceans and hemimetabolous insects, there exist considerable similarities in the mechanisms by which accretion of the compound eyes and growth of the optic lobes is achieved, suggesting an evolutionary conservation of these mechanisms.

Neurogenesis in the thoracic neuromeres of two crustaceans with different types of metamorphic development

The mode of embryonic and larval development and the ethology of metamorphosis in the spider crab and the American lobster are very different, and we took advantage of this to compare neuronal development in the two species. The goals of this study were to discover whether the differences in the maturation of the neuromuscular system in the pereopods and the metamorphic changes of motor behavior between the two species are reflected at the level of the developing nervous system ('neurometamorphosis'). Furthermore, we wanted to broaden our understanding of the mechanisms that govern neuronal development in arthropods. Proliferation of neuronal stem cells in thoracic neuromeres 4-8 of the lobster Homarus americanus and the crab Hyas araneus was monitored over the course of embryonic and larval development using the in vivo incorporation of bromodeoxyuridine (BrdU). Neuropil structure was visualized using an antibody against Drosophila synapsin. While proliferation of neuronal precursors has ceased when embryogenesis is 80 % complete (E80%) in the lobster thoracic neuromeres, proliferation of neuroblasts in the crab persists throughout embryonic development and into larval life. The divergent temporal patterns of neurogenesis in the two crustacean species can be correlated with differences in larval life style and in the degree of maturation of the thoracic legs during metamorphic development. Several unusual aspects of neurogenesis reported here distinguish these crustaceans from other arthropods. Lobsters apparently lack a postembryonic period of proliferation in the thoracic neuromeres despite the metamorphic remodeling that takes place in the larval stages. In contrast, an increase in mitotic activity towards the end of embryonic development is found in crabs, and neuroblast proliferation persists throughout the process of hatching into the larval stages. In both E20% lobster embryos and mid-embryonic crabs, expression of engrailed was found in a corresponding set of neurons and putative glial cells at the posterior neuromere border, suggesting that these cells have acquired similar specific identities and might, therefore, be homologous. None of the BrdU-labeled neuroblasts (typically 6-8 per hemineuromere over a long period of embryogenesis) was positive for engrailed at this and subsequent stages. Our findings are discussed in relation to the spatial and temporal patterns of neurogenesis in insects.

Adult treatment with haloperidol increases dentate granule cell proliferation in the gerbil hippocampus

Male gerbils were bred and reared grouped under enriched semi-natural environmental conditions. The objective of the present study was to examine the influence of an acute treatment with the neuroleptic haloperidol on adult granule cell neurogenesis in the hippocampus. For that purpose, at the age of postnatal day 90 adult animals received 4 challenges of either haloperidol (5 mg/kg, i.p.) or saline. Proliferation of granule cells was identified by in-vivo labeling with 5-bromo-2'-desoxyuridine (BrdU) which was applied 1 hour after the final dose of haloperidol. BrdU-labeled granule cell nuclei were identified in consecutive horizontal slices along the mid-septotemporal axis of the hippocampus and light-microscopically quantified 7 days after the BrdU-labeling. It was found that in both saline- and haloperidol-treated animals there was a highly significant spatial septotemporal gradient in granular cell proliferation with numbers of BrdU-labeled cells gradually declining from the septal towards the temporal pole. The acute treatment with haloperidol stimulated granule cell proliferation by about 75% and the septotemporal gradient of mitotic activity became significantly enhanced. The present results are discussed with regard to known factors regulating cell proliferation in the hippocampus and other cell systems.

Social environment alters both ontogeny of dopamine innervation of the medial prefrontal cortex and maturation of working memory in gerbils (Meriones unguiculatus)

Male gerbils (Meriones unguiculatus) were bred and reared either grouped under enriched environmental conditions or isolated under impoverished environmental conditions. The objective of the present study was to examine the influence of social environment on structural and functional ontogeny of the medial prefrontal cortex (mPFC). In this respect, we investigated the maturation of both prefrontal dopamine (DA) innervation and working memory. For that purpose, at the age of postnatal day 90, prefrontal DA fibers were stained immunocytochemically using an antibody against glutaraldehyde-conjugated DA and innervation density was determined by means of a computer controlled program for image analysis. In order to evaluate environmental effects on working memory, 90-day-old gerbils were tested for y-maze delayed alternation. It was found that, isolation produced a significant and severe restraint of the maturation of prefrontal DA innervation, leading to fiber densities which were 56% below those in group-reared gerbils. Isolation also induced a significant impairment of delayed alternation performance on the y-maze indicating that obvious deficits in working memory had developed under restricted rearing conditions. The present results are discussed with regard to activity-dependent postnatal maturation of the cortex and adaptive neuroplasticity.

A developmental study of serotonin-immunoreactive neurons in the larval central nervous system of the spider crab Hyas araneus (Decapoda, Brachyura)

Larval development in crabs is characterized by a striking double metamorphosis in the course of which the animals change from a pelagic to a benthic life style. The larval central nervous system has to provide an adequate behavioural repertoire during this transition. Thus, processes of neuronal reorganization and refinement of the early larval nervous system could be expected to occur in the metamorphosing animal. In order to follow identified sets of neurons throughout metamorphosis, whole mount preparations of the brain and ventral nerve cord of laboratory reared spider crab larvae (Hyas araneus) were labelled with an antibody against the neurotransmitter serotonin. The system of serotonin-immunoreactive cell bodies, fibres and neuropils is well-developed in newly hatched larvae. Most immunoreactive structures are located in the protocerebrum, with fewer in the suboesophaegeal ganglia, while the thoracic and abdominal ganglia initially comprise only a small number of serotonergic neurons and fibres. However, there are significant alterations in the staining pattern through larval development, some of which are correlated to metamorphic events. Accordingly, new serotonin-immunoreactive cells are added to the early larval set and the system of immunoreactive fibres is refined. These results are compared to the serotonergic innervation in other decapod crustaceans.

A single dose of methamphetamine in neonatal gerbils affects adult prefrontal gamma-aminobutyric acid innervation

A single non-invasive dose of methamphetamine (50 mg/kg i.p.) was administered to neonatal male gerbils (Meriones unguiculatus) aged 14 days. At the age of postnatal day 90, the gamma-aminobutyric acid (GABA) immunoreactive profiles were electron microscopically quantified in the prelimbic area of the prefrontal cortex and compared with those of saline-treated controls. This early solitary drug challenge resulted in adult GABAergic innervation densities which were approximately 40% above those of saline-treated controls.

Immunocytochemical detection of acetylated alpha-tubulin and Drosophila synapsin in the embryonic crustacean nervous system

The caridean shrimp Palaemonetes argentinus Nobili is well suited for studying developmental aspects of the crustacean nervous system due to its rapid embryonic development and short reproductive cycle. In the present paper, we demonstrate the pattern of central axonal pathways in embryos of this species by immunohistochemical detection of acetylated alpha-tubulin. Development of the neuropil was elucidated by using an antibody to a Drosophila synapsin. In the ventral nerve cord, the segmental axonal scaffold consists of the paired lateral connectives, a median connective, and the anterior and posterior commissures. Three nerve roots were found to branch off each ganglion anlage, i.e. the main segmental nerve root, a smaller posterior nerve and the intersegmental nerve. However, this pattern is different in the mandibular segment where no intersegmental nerve and only one commissure was encountered. The anterior part of the brain consists of a tritocerebral and a deutocerebral anlage as well asthe anlage of the medial protocerebrum. The latter is connected to the eyestalk via the protocerebral tract. The sequence of development of the eyestalk ganglia was demonstrated in specimens which were stained with the anti-synapsin antibody. The medulla terminalis and medulla interna are the first neuropils to appear and are still fused in early stages. Later, the medulla interna splits off the medulla terminalis. The lamina ganglionaris is the last of the eyestalk neuropils to develop. These findings prove that immunocytochemistry against acetylated alpha-tubulin and synapsin are valuable tools for studying the development of the crustacean nervous system.

Pharmacologically induced neural plasticity in the prefrontal cortex of adult gerbils (Meriones unguiculatus)

Using a selective antibody serum against glutaraldehyde-conjugated gamma-aminobutyric acid (GABA), GABAergic neurons were identified in the medial prefrontal cortex of young adult gerbils (Meriones unguiculatus) following a single non-invasive dose of methamphetamine (25 mg/kg i.p.) applied at the age of 90 days. GABA-immunoreactive profiles were electron microscopically counted in a defined test field (0.875 mm2) covering the prefrontal prelimbic area after a single dose of either methamphetamine or saline. Within 30 days following the drug challenge the density of GABAergic innervation significantly increased by about 20%. Several lines of previous investigation indicate that a single dose of methamphetamine is an appropriate stimulus to cause selective autotoxic destruction of certain prefrontal dopamine fibres due to drug-induced hyperactivation. There is further indication of postsynaptic and transneuronal neuroplasticity since the densities of dendritic spines on prefrontal pyramidal cells went through a significant sequence of post-drug gain and loss. These structural dynamics resemble typical alterations seen after classical mechanical or chemical lesioning in other regions of the brain. The present results on drug-induced reactive neuroplasticity are discussed together with the current understanding of stimulus-induced adaptive reorganization in the mammalian central nervous system.

Dopamine and the regulation of cell proliferation in gerbil (Meriones unguiculatus) pyloric mucosa

The epithelium of the digestive system mucosa consists of a highly dynamic cell population. The conditions under which mitotic activity in the gastrointestinal epithelium is regulated is as yet poorly understood. Nevertheless, it is assumed that some biogenic amines might be involved. Having demonstrated that dopaminergic cells occur in the stomach of gerbils (Meriones unguiculatus), in the present study we examined the influence of dopamine antagonist haloperidol on the proliferation of epithelial cells in the mucosa of the stomach. Proliferating cells were detected immunocytochemically and quantified after in-vivo labeling with 5-bromo-2'-desoxyuridine in both haloperidol- and saline-treated animals. The results show that acute doses of haloperidol significantly increases the proliferation rate in the pyloric mucosa, suggesting that dopamine plays a probable modulatory role in the regulation of mitotic activity. These findings are discussed with regard to the role of paraneurons in regulating epithelial mitosis.

Demonstration of dopamine immunoreactivity in open and closed type endocrine cells of gerbil (Meriones unguiculatus) stomach

Dopamine-immunoreactive cells were identified in the stomach of gerbils using a selective antibody against glutaraldehyde-conjugated dopamine. In the pyloric area dopamine-containing cells were exclusively localized in the basal part of the mucous membrane, whereas in the fundic area dopaminergic cells were seen throughout the basodistal extent of the mucous membrane. Dopamine-containing cells belong to the class of closed and open type endocrine cells and were found in the fundic area and in the pyloric area respectively. These findings are discussed along with the likely modulatory function of dopamine in peripheral tissues.

Neurogenesis in the developing crab brain: postembryonic generation of neurons persists beyond metamorphosis

A considerable amount of information is available about the structure and function of the central nervous system in adult crustaceans. However, little effort has been directed toward understanding embryonic and larval neurogenesis in these animals. In the present study we recorded neurogenesis in the brain of laboratory-reared larvae of the spider crab Hyas araneus. Proliferating cells were detected immunocytochemically after in vivo labeling with 5-bromo-2'-deoxyuridine. This method has already been used to study the proliferation of neuroblasts in the ventral nerve cord of spider crab larvae. In the brain, a set of mitotically highly active neuroblasts was found in newly hatched zoea 1 larvae. These neuroblasts are individually identifiable due to their position and therefore a schematic map of the cerebral neuroblasts could be established. The number of active neuroblasts is high from hatching throughout the molt to the zoea 2. This proliferative action then decreases dramatically and has ceased at the time of first metamorphosis toward the megalopa larva. However, many ganglion mother cells born by unequal division of neuroblasts then go through their final division throughout the subsequent megalopa stage. In the brain, all mitotic activity has ceased at the time of second metamorphosis with the exception of a cluster of labeled nuclei within the olfactory lobe cells. In this cluster, the generation of neurons persists beyond the second metamorphosis into the crab 1 stage. Meanwhile, the neuropil volume of the olfactory lobes increases 10-fold from hatching to the crab 1. These results are discussed with regard to reports on neuronal proliferation during adult life in insects and rodents.

Ontogeny of PFC-related behaviours is sensitive to a single non-invasive dose of methamphetamine in neonatal gerbils (Meriones unguiculatus)

A single dose of methamphetamine (50 mg/kg; i.p.) was administered to neonatal male gerbils (Meriones unguiculatus) aged 14 days, and adult prefrontal cortex (PFC)-related behaviours were analysed and compared with saline-treated controls at the age of postnatal day 90. For that purpose, animals were tested for open-field activities and y-maze delayed alternation. This solitary and non-invasive drug challenge, which has recently been found to initiate serious restraint in maturation of the mesoprefrontal dopamine (DA)-system (Dawirs et al., 1994), induces a significant delayed alternation impairment as well as significant increases in open-field motor activity and emotionality. Since an undisturbed development of the prefrontal DA-innervation seems to be a precondition for the maturation of normal PFC-related behaviours, a single early methamphetamine impact may be a suitable animal model for further investigation of structural and functional aspects of non-invasively induced behavioural deficits in rodents. The present results are discussed with regard to the assumption that hypofunctional mesoprefrontal DA-systems might be basic to schizophrenic behaviours in man.

The postnatal maturation of dopamine innervation in the prefrontal cortex of gerbils (Meriones unguiculatus) is sensitive to an early single dose of methamphetamine. A quantitative immunocytochemical study

Dopamine (DA)-immunoreactivity was investigated in the prefrontal cortex (PFC) of 90 day old adult male gerbils (Meriones unguiculatus) after they had received a single dose of either methamphetamine (50 mg/kg; i.p.) or saline at the age of postnatal day 14. For that purpose, a selective and sensitive antibody directed against glutaraldehyde-conjugated dopamine was applied. All detectable fragments of dopamine-immunoreactive fibres were identified in consecutive frontal sections of the pregenual prefrontal cortex, and their total numbers and total length were determined in the medial (mPFC) and orbital prefrontal cortex (oPFC). The results indicate that a single application of methamphetamine during early postnatal development caused a significant and severe restraint of the subsequent maturation of the prefrontal dopamine-innervation. Although, on postnatal day 14, the total dopamine-immunoreactivity had only attained about 4% (mPFC) and 7% (oPFC) of the regular adult values, this solitary pharmacological challenge entailed final adult innervation densities which were about 38% (mPFC) and 50% (oPFC) below those of the controls. Considering the pivotal role which mesoprefrontal dopaminergic afferents play in morphogenesis and regular functioning, the present results are discussed with current understanding of structural and functional plasticity during maturation of the prefrontal cortex.

Indication of methamphetamine-induced reactive synaptogenesis in the prefrontal cortex of gerbils (Meriones unguiculatus)

A single dose of methamphetamine (25 mg/kg i.p.) was administered to young adult gerbils (Meriones unguiculatus) aged 90 days and the number of spices was determined along 40-microns segments of basal, lateral and apical dendrites of pyramidal cells in layers III and V of the prefrontal cortex, after 1.5, 7, 20 and 30 days. The density of spines rapidly increased by more than 80% within 7 days after drug challenge, and subsequently returned to the original normal values within about 2 weeks. Thirty days after drug administration the density of dendritic spines was slightly, but significantly, less than control values (about 5%). The density of spines was likewise affected in layer III and V neurones, irrespective of the spatial domain of their dendritic ramifications. Since several lines of investigation indicate that methamphetamine can cause the destruction of dopaminergic nerve terminals in the mammalian forebrain, the present results are discussed against the background of current concepts about reactive synaptic reorganization and adaptive remodelling of neural circuits in the central nervous system.

Demonstration of dopamine-immunoreactive cells in the proximal convoluted tubule of gerbil (Meriones unguiculatus) kidney

We investigated dopamine immunoreactivity in the kidney of gerbils (Meriones unguiculatus). For that purpose a sensitive and selective antibody against glutaraldehyde-conjugated dopamine was applied. Dopamine-immunoreactive cells were found in the epithelium of the proximal convoluted tubule, where these cells revealed a typical segment-like distribution pattern. Dopamine-immunoreactive precipitates were small and concentrated at the apical pole of the labeled cells. This study has directly identified dopamine as a constituent of certain cells of the proximal convoluted tubule in gerbils. The functional significance of dopamine in these cells is discussed in relation to the present view of renal dopaminergic actions.

Demonstration of dopamine-immunoreactive cells in the gastrointestinal tract of gerbils (Meriones unguiculatus)

We investigated dopamine immunoreactivity in the small intestine of gerbils (Meriones unguiculatus), using a sensitive and selective antibody against glutaraldehyde-conjugated dopamine. Dopamine-immunoreactive cells were found within the mucosal epithelium along the entire extent of the small intestine. Labeled cells were regularly distributed in the upper half of the intestinal villi, basally attached to the basement membrane and always reaching as far as the epithelial surface. Dopamine-containing cells revealed a spindle-like shape, and both light and electron microscopic characteristics relate them to typical open-type gut endocrine cells. Thus, this current study directly identified dopamine as a probable secretory product in basal granulated cells of the small intestine. The functional significance of these cells is discussed in relation to the current view of dopaminergic actions in peripheral tissues.

Naturally occurring degrading events in axon terminals of the dentate gyrus and stratum lucidum in the spiny mouse (Acomys cahirinus) during maturation, adulthood and aging

The naturally occurring dynamics of presynaptic axon terminals were investigated in the dentate gyrus and stratum lucidum of the spiny mouse (Acomys cahirinus) during maturation, adulthood and aging. A sensitive and selective silver-staining technique was applied to analyze neuronal lysosome accumulation (LA), indicating synaptic degradation during development. LA was quantified by counting silver grains in the inner third and outer two thirds of the molecular layer, granular layer, and the infragranular layer of the dentate gyrus, and in the strata oriens, pyramidale, lucidum and radiatum of the medial and distal regio inferior on postnatal days 21, 28, 95, 730, and 1,460. In young and adult animals, LA was most abundant within the inner molecular layer. When animals grew older, LA densities obviously decreased in the inner molecular layer but increased in the outer molecular layer. Within the stratum lucidum only the distal regio inferior showed an extremely high LA density on postnatal day 21, dramatically decreasing thereafter and reaching adult low values during the first postnatal month. By electron microscopy in the inner molecular layer we found LA in large synaptic boutons and small terminals both with distinct synaptic contact zones. Degrading presynaptic profiles may further accumulate dense bodies, zones with completely disorganized cytoplasm, and lamellarly organized whorled membrane debris. In the distal regio inferior comparable phenomena were observed in typical mossy fiber boutons. Despite these degrading events, no electron-dense degenerating terminals were found. These results on naturally occurring nondegenerative synaptic degradation are discussed with current concepts of synaptic turnover and remodelling in the developing, adult and aging brain.

Age-related toxicity in prefrontal cortex and caudate-putamen complex of gerbils (Meriones unguiculatus) after a single dose of methamphetamine

Single, intermediate to large doses (6-60 mg/kg) of methamphetamine were applied to study the acute neurotoxic effects in developing male gerbils (up to 24 months). A sensitive silver-staining method was used to analyze the toxicity of methamphetamine by light and electron-microscopy. It was shown that treatment with the drug degraded synaptic components, as well as a small population of neurones in the caudate-putamen complex accompanied by accumulation of lysosomes in fibers and axon terminals. In juveniles, methamphetamine in doses of 25-60 mg/kg, resulted in accumulation of lysosomes, selectively in the prefrontal cortex. In young adults, only about half of these doses were sufficient to produce consistent and/or additional effects in the caudate-putamen complex. When the gerbils grew older than 8 months, treatment with drug led to accumulation of lysosomes, exclusively in the caudate-putamen, with acute doses ranging from 6 to 12 mg/kg. Acute neurotoxicity with methamphetamine has thus been induced by doses, which hitherto have been claimed to produce behavioural sensitization. Since dopamine (DA) seems the most likely transmitter to be affected, age-related differences in methamphetamine-induced neurotoxicity are discussed in relation to the background of developing DA-response systems, which are still changing in pattern during ageing.

Single doses of methamphetamine cause changes in the density of dendritic spines in the prefrontal cortex of gerbils (Meriones unguiculatus)

Single doses of methamphetamine (25 mg/kg) were administered to adult gerbils. All detectable spines were counted along defined segments of basal, apical and lateral dendrites of Golgi-impregnated pyramidal cells in the medial prefrontal cortex (layers III and V) and the parietal cortex (layer V). These two areas were selected because previous investigations had shown methamphetamine-induced neurotoxicity in prefrontal cortex but not in parietal cortex. The frequencies of dendritic spines in methamphetamine-treated gerbils were found to be significantly increased in the prefrontal cortex, while no significant change was found in the parietal cortex.

Neuronal lysosome accumulation in degrading synapses of sensory-motor and limbic subsystems in the duck Anas platyrhynchos: indication of rearrangements during avian brain development?

Brains of developing duck embryos and ducklings were analysed daily by light microscopy after complete serial brain sectioning and lysosome staining (Gallyas technique), providing insight into synaptic degradation and degeneration during short periods of synaptogenesis. Both regional and temporal shifting pattern of lysosome accumulation (LA) in degraded synapses were detected in sensory-motor pathways during the course of development. LA occurred in sensory projections of embryos, and proceeded from forebrain sensory fields toward limbic regions and finally motor projections. LA disappeared from these structures at the age of 4-6 weeks. LA was analysed ultrastructurally in selected sensory, limbic and motor regions indicating that lysosomes selectively accumulated in transient synapses, leaving parts of either pre- or postsynaptic elements untouched. In no case did denervated neurons exhibit any signs of cell death. Apparently, the LA phenomenon seems critical in terms of both irreversible elimination and remodelling of persisting synapses. Thus, neuronal rearrangement mediated by lysosomal degradation, i.e. degeneration of synaptic components, is supposed to be an integral constituent of synaptogenesis during adaptive processes in sensory-motor systems. These results are discussed with regard to developing brain functions during behavioural adaptation of this precocious bird.