Hypoplasia of dopaminergic neurons by hypoxia-induced neurotoxicity is associated with disrupted swimming development of larval zebrafish

Hypoxic injury to the developing brain increases the risk of permanent behavioral deficits, but the precise mechanisms of hypoxic injury to the developing nervous system are poorly understood. In this study, we characterized the effects of developmental hypoxia (1% pO₂ from 24 to 48 h post-fertilization, hpf) on diencephalic dopaminergic (DA) neurons in larval zebrafish and the consequences on the development of swimming behavior. Hypoxia reduced the number of diencephalic DA neurons at 48 hpf. Returning zebrafish larvae to normoxia after the hypoxia (i.e., hypoxia-recovery, HR) induced reactive oxygen species (ROS) accumulation. Real-time qPCR results showed that HR caused upregulation of proapoptotic genes, including p53 and caspase3, suggesting the potential for ROS-induced cell death. With HR, we also found an increase in TUNEL-positive DA neurons, a persistent reduction in the number of diencephalic DA neurons, and disrupted swimming development and behavior. Interestingly, post-hypoxia (HR) with the antioxidant N-acetylcysteine partially restored the number of DA neurons and spontaneous swimming behavior, demonstrating potential recovery from hypoxic injury. The present study provides new insights for understanding the mechanisms responsible for motor disability due to developmental hypoxic injury.

Dopaminergic Co-Regulation of Locomotor Development and Motor Neuron Synaptogenesis is Uncoupled by Hypoxia in Zebrafish

Hypoxic injury to the developing human brain is a complication of premature birth and is associated with long-term impairments of motor function. Disruptions of axon and synaptic connectivity have been linked to developmental hypoxia, but the fundamental mechanisms impacting motor function from altered connectivity are poorly understood. We investigated the effects of hypoxia on locomotor development in zebrafish. We found that developmental hypoxia resulted in decreased spontaneous swimming behavior in larva, and that this motor impairment persisted into adulthood. In evaluation of the diencephalic dopaminergic neurons, which regulate early development of locomotion and constitute an evolutionarily conserved component of the vertebrate dopaminergic system, hypoxia caused a decrease in the number of synapses from the descending dopaminergic diencephalospinal tract (DDT) to spinal cord motor neurons. Moreover, dopamine signaling from the DDT was coupled jointly to motor neuron synaptogenesis and to locomotor development. Together, these results demonstrate the developmental processes regulating early locomotor development and a requirement for dopaminergic projections and motor neuron synaptogenesis. Our findings suggest new insights for understanding the mechanisms leading to motor disability from hypoxic injury of prematurity.

Hypoxia and connectivity in the developing vertebrate nervous system

The developing nervous system depends upon precise regulation of oxygen levels. Hypoxia, the condition of low oxygen concentration, can interrupt developmental sequences and cause a range of molecular, cellular and neuronal changes and injuries. The roles and effects of hypoxia on the central nervous system (CNS) are poorly characterized, even though hypoxia is simultaneously a normal component of development, a potentially abnormal environmental stressor in some settings, and a clinically important complication, for example of prematurity. Work over the past decade has revealed that hypoxia causes specific disruptions in the development of CNS connectivity, altering axon pathfinding and synapse development. The goals of this article are to review hypoxia's effects on the development of CNS connectivity, including its genetic and molecular mediators, and the changes it causes in CNS circuitry and function due to regulated as well as unintended mechanisms. The transcription factor HIF1α is the central mediator of the CNS response to hypoxia (as it is elsewhere in the body), but hypoxia also causes a dysregulation of gene expression. Animals appear to have evolved genetic and molecular responses to hypoxia that result in functional behavioral alterations to adapt to the changes in oxygen concentration during CNS development. Understanding the molecular pathways underlying both the normal and abnormal effects of hypoxia on CNS connectivity may reveal novel insights into common neurodevelopmental disorders. In addition, this Review explores the current gaps in knowledge, and suggests important areas for future studies.

Summary: The nervous system's exposure to hypoxia has developmental and clinical relevance. In this Review, the authors discuss the effects of hypoxia on the development of the CNS, and its long-term behavioral and neurodevelopmental consequences.

Approach to Management of Eyes with no Light Perception after Open Globe Injury

Loss of light perception (LP) after open globe injury (OGI) does not necessarily mean the patient will have permanent complete visual loss. Findings that seem to be associated reliably with permanent profound vision loss after OGI include optic nerve avulsion, optic nerve transection, and profound loss of intraocular contents, which can be identified with CT/MRI imaging albeit with varying degrees of confidence. Eyes with NLP after OGI that undergo successful primary repair with intact optic nerves may be considered for additional surgery, particularly if there is: (1) recovery of LP on the first day after primary repair; (2) treatable pathology underlying NLP status (e.g., extensive choroidal hemorrhage, dense vitreous and subretinal hemorrhage); (3) NLP in the fellow eye. We counsel patients that the chance of recovering ambulatory vision under these circumstances is very low (~5%).

Solar optics-based active panel for solar energy storage and disinfection of greywater

Smart city and innovative building strategies are becoming increasingly more necessary because advancing a sustainable building system is regarded as a promising solution to overcome the depleting water and energy. However, current sustainable building systems mainly focus on energy saving and miss a holistic integration of water regeneration and energy generation. Here, we present a theoretical study of a solar optics-based active panel (SOAP) that enables both solar energy storage and photothermal disinfection of greywater simultaneously. Solar collector efficiency of energy storage and disinfection rate of greywater have been investigated. Due to the light focusing by microlens, the solar collector efficiency is enhanced from 25% to 65%, compared to that without the microlens. The simulation of greywater sterilization shows that 100% disinfection can be accomplished by our SOAP for different types of bacteria including Escherichia coli. Numerical simulation reveals that our SOAP as a lab-on-a-wall system can resolve the water and energy problem in future sustainable building systems.

Temporal Dysynchrony in brain connectivity gene expression following hypoxia

Background

Despite the fundamental biological importance and clinical relevance of characterizing the effects of chronic hypoxia exposure on central nervous system (CNS) development, the changes in gene expression from hypoxia are unknown. It is not known if there are unifying principles, properties, or logic in the response of the developing CNS to hypoxic exposure. Here, we use the small vertebrate zebrafish (Danio rerio) to study the effects of hypoxia on connectivity gene expression across development. We perform transcriptional profiling at high temporal resolution to systematically determine and then experimentally validate the response of CNS connectivity genes to hypoxia exposure.

Results

We characterized mRNA changes during development, comparing the effects of chronic hypoxia exposure at different time-points. We focused on changes in expression levels of a subset of 1270 genes selected for their roles in development of CNS connectivity, including axon pathfinding and synapse formation. We found that the majority of CNS connectivity genes were unaffected by hypoxia. However, for a small subset of genes hypoxia significantly affected their gene expression profiles. In particular, hypoxia appeared to affect both the timing and levels of expression, including altering expression of interacting gene pairs in a fashion that would potentially disrupt normal function.

Conclusions

Overall, our study identifies the response of CNS connectivity genes to hypoxia exposure during development. While for most genes hypoxia did not significantly affect expression, for a subset of genes hypoxia changed both levels and timing of expression. Importantly, we identified that some genes with interacting proteins, for example receptor/ligand pairs, had dissimilar responses to hypoxia that would be expected to interfere with their function. The observed dysynchrony of gene expression could impair the development of normal CNS connectivity maps.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2638-x) contains supplementary material, which is available to authorized users.

Methamphetamine-, d-Amphetamine-, and p-Chloroamphetamine-Induced Neurotoxicity Differentially Effect Impulsive Responding on the Stop-Signal Task in Rats

Abused amphetamines, such as d-amphetamine (AMPH) and methamphetamine (METH), are highly addictive and destructive to health and productive lifestyles. The abuse of these drugs is associated with impulsive behavior, which is likely to contribute to addiction. The amphetamines also differentially damage dopamine (DA) and serotonin (5-HT) systems, which regulate impulsive behavior; therefore, exposure to these drugs may differentially alter impulsive behavior to effect the progression of addiction. We examined the impact of neurotoxicity induced by three amphetamines on impulsive action using a stop-signal task in rats. Animals were rewarded with a food pellet after lever pressing (i.e., a go trial), unless an auditory cue was presented and withholding lever press gained reward (i.e., a stop trial). Animals were trained on the task and then exposed to a neurotoxic regimen of either AMPH, p-chloroamphetamine (PCA), or METH. These regimens preferentially reduced DA transporter levels in striatum, 5-HT transporter levels in prefrontal cortex, or both, respectively. Assessment of performance on the stop-signal task beginning 1 week after the treatment revealed that AMPH produced a deficit in go-trial performance, whereas PCA did not alter performance on either trial type. In contrast, METH produced a deficit in stop-trial performance (i.e., impulsive action) but not go-trial performance. These findings suggest that the different neurotoxic consequences of substituted amphetamines are associated with different effects on inhibitory control over behavior. Thus, the course of addiction and maladaptive behavior resulting from exposure to these substances is likely to differ.

Apolipoprotein B: novel indicator of elevated intraocular pressure

PURPOSE

Many studies have reported associations between elevated intraocular pressure (IOP) and systemic health parameters, which suggest a common mechanism links IOP elevation and various related cardiometabolic risk factors. Furthermore, according to a recent study, serum apolipoprotein B (APO B) level is a predictor of coronary artery disease. This study was undertaken to analyse the relationship between serum apolipoprotein levels and IOP.

METHODS

Healthy people (28,852) who attended a community hospital for a health checkup between January 2011 and December 2013 were enroled in the study. We measured age, body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP), serum levels of total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and apolipoprotein A1 (APO A1) and APO B, APO B/APO A1 ratios, and IOP.

RESULTS

Univariate regression analysis showed IOP was positively correlated with BMI, SBP, DBP, TC, LDL-C, TG, APO B, and APO B/APO A1 (P<0.001), and negatively correlated with HDL-C (P<0.001). On the other hand, multivariate regression analysis adjusted for age, BMI, SBP, and DBP, revealed IOP was positive correlated with TC, TG, LDL-C, APO B, and APO B/APO A1, and negatively correlated with HDL-C (all <0.05).

CONCLUSIONS

Among the various lipid profiles investigated, APO B was found to be most strongly correlated with IOP, regardless of sex. Additional studies are required to confirm the validity of apolipoprotein level as an index for predicting IOP.

Perseverative behavior in rats with methamphetamine-induced neurotoxicity

Methamphetamine induces monoamine depletions thought to contribute to cognitive and behavioral dysfunctions. Previously, we reported that methamphetamine-induced neurotoxicity is associated with impaired formation of stimulus-response associations. Additionally, subjective observations suggested that behavioral flexibility might be affected. Thus, the present study examined whether methamphetamine neurotoxicity induces perseverative behavior. Rats were pretreated with (±)-methamphetamine (4 × 10 mg/kg, 2-hr intervals) or saline. Three weeks later, rats were trained to press a lever on one side of an operant chamber and then retrieve the reinforcer from a magazine on the opposite side until they reached criterion (>50 reinforcers/30-min). After four consecutive sessions performing the task at criterion, rats were sacrificed and brains removed for monoamine determinations. Methamphetamine-pretreated rats had ∼50% loss of striatal dopamine and prefrontal serotonin. Methamphetamine- and saline-pretreated rats were not different in the number of sessions required to reach criterion or in the total numbers of lever presses and/or head entries made across the four consecutive sessions at criterion-level performance. However, methamphetamine-pretreated rats earned fewer reinforcers, because they made extra lever-presses and head entries when they should have been retrieving the reinforcer or returning to the lever. Latencies for methamphetamine-pretreated rats to switch between the two behaviors also were significantly slower than latencies for controls. Interestingly, the degree of additional lever-presses negatively correlated with serotonin-transporter binding in the prefrontal cortex, even in saline-pretreated controls. These data suggest that methamphetamine-induced partial monoamine toxicity is associated with perseveration and that the degree of perseveration may depend on serotonin innervation of the frontal cortex.

Impaired formation of stimulus-response, but not action-outcome, associations in rats with methamphetamine-induced neurotoxicity

Methamphetamine (METH) induces neurotoxic changes, including partial striatal dopamine depletions, which are thought to contribute to cognitive dysfunction in rodents and humans. The dorsal striatum is implicated in action-outcome (A-O) and stimulus-response (S-R) associations underlying instrumental learning. Thus, the present study examined the long-term consequences of METH-induced neurotoxicity on A-O and S-R associations underlying appetitive instrumental behavior. Rats were pretreated with saline or a neurotoxic regimen of METH (4 × 7.5-10 mg/kg). Rats trained on random ratio (RR) or random interval (RI) schedules of reinforcement were then subjected to outcome devaluation or contingency degradation, followed by an extinction test. All rats then were killed, and brains removed for determination of striatal dopamine loss. The results show that: (1) METH pretreatment induced a partial 45-50% decrease in striatal dopamine tissue content in dorsomedial and dorsolateral striatum; (2) METH-induced neurotoxicity did not alter acquisition of instrumental behavior on either RR or RI schedules; (3) outcome devaluation and contingency degradation similarly decreased responding in saline- and METH-pretreated rats trained on the RR schedule, suggesting intact A-O associations guiding behavior; (4) outcome devaluation after training on the RI schedule decreased extinction responding only in METH-pretreated rats, suggesting impaired S-R associations. Overall, these data suggest that METH-induced neurotoxicity, possibly due to impairment of the function of dorsolateral striatal circuitry, may decrease cognitive flexibility by impairing the ability to automatize behavioral patterns.

Signal intensities of radiolabeled cRNA probes used alone or in combination with non-isotopic in situ hybridization histochemistry

This study addressed the question of whether radioactive hybridization signal intensities are reduced in combined isotopic and non-isotopic double in situ hybridization (DISH) compared with those in single in situ hybridization (ISH). Non-isotopic digoxigenin (Dig)-labeled hybrids were detected using an alkaline phosphatase (AP) enzymatic reaction which results in nitroblue tetrazolium chloride (NBT)/5-bromo-4-chloro-3-indolyl phosphate (BCIP)-salt precipitation that could shield S35-radiation from penetrating to the surface. Sections were plastic coated of with 2% parlodion to prevent a chemical reaction between AP and developer during processing of the photosensitive emulsion, which could further reduce radioactive hybridization signal detection by autoradiography. We used DISH with a hybridization cocktail of radioactive S35- and Dig-labeled GAD67 cRNA probes. In order to avoid competition for the same complementary sequence, the probes were directed towards different sequences of the glutamic acid decarboxylase (GAD67) mRNA, resulting in co-detection of isotopic and non-isotopic hybrids in close to 100% of GAD67 positive cells. Quantitation of autoradiograms showed that there was no reduction of autoradiographic signal intensity from S35-labeled hybrids in the presence of Dig-labeled hybrids. Plastic coating of single or dual hybridized sections did not reduce the radioactive signal intensity. When mRNAs for nicotinic acetylcholine receptor (nAChR) subunits were detected with subunit specific S35-labeled cRNA probes in GAD67 hippocampal interneurons the total numbers of nAChR subunit expressing cells remained the same in single or double hybridized sections even for low abundant mRNAs. Together, these results indicate that combined radioactive and non-radioactive DISH does not interfere with the detection of the radiation signal from the S35-labeled hybrids, and neither specificity nor sensitivity is compromised.

Expression of neuronal nicotinic acetylcholine receptor subunit mRNAs in rat hippocampal GABAergic interneurons

Hippocampal inhibitory interneurons are a diverse population of cells widely scattered in the hippocampus, where they regulate hippocampal circuit activity. The hippocampus receives cholinergic projections from the basal forebrain, and functional studies have suggested the presence of different subtypes of nicotinic acetylcholine receptors (AChRs) on gamma-aminobutyric acid (GABA)ergic interneurons. Single-cell polymerase chain reaction analysis had confirmed that several nAChR subunit mRNAs are co-expressed with glutamate decarboxylase 67 (GAD67), the marker for GABAergic interneurons. In this anatomical study, we systematically investigated the co-expression of GAD67 with different nAChR subunits by using double in situ hybridization with a digoxigenin-labeled GAD67 probe and (35)S-labeled probes for nAChR subunits (alpha2, alpha3, alpha4, alpha5, alpha6, alpha7, beta2, beta3, and beta4). The results revealed that most GAD67-positive interneurons expressed beta2, and 67 % also expressed alpha7 mRNA. In contrast, mRNA expression of other subunits was limited; only 13 % of GAD67-positive neurons co-expressed alpha4, and less than 10% expressed transcripts for alpha2, alpha3, alpha5, or beta4. Most GAD67/alpha2 co-expression was located in CA1/CA3 stratum oriens, and GAD67/alpha5 co-expression was predominantly detected in CA1/CA3 stratum radiatum/lacunosum moleculare and the dentate gyrus. Expression of alpha6 and beta3 mRNAs was rarely detected in the hippocampus, and mRNAs were not co-expressed with GAD67. These findings suggest that the majority of nicotinic responses in GABAergic interneurons should be mediated by a homomeric alpha7 or heteromeric alpha7*-containing nAChRs. Other possible combinations such as alpha2beta2*, alpha4beta2*, or alpha5beta2* heteromeric nAChRs could contribute to functional nicotinic response in subsets of GABAergic interneurons but overall would have a minor role.

Postnatal expression of alpha2 nicotinic acetylcholine receptor subunit mRNA in developing cortex and hippocampus

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated cation channels composed of alpha and beta subunits. nAChR subunit expression is highly regulated during development. Previous studies have revealed increased expression of alpha3, alpha5, alpha7, and beta4 subunit mRNAs and alpha7 binding sites during hippocampal and cortical development. Here, we examined the expression of alpha2 subunit mRNA in rat cortex and hippocampus using highly sensitive radioactive in situ hybridization. alpha2 Subunit mRNA expression was first detected at P3 in cortex and hippocampus. During postnatal development the distribution of alpha2 subunit mRNA expression was spatially similar to the one found in adult, exhibiting highly restricted expression in scattered cells mostly in cortical layer V and retrosplenial cortex, and in scattered cells in CA1/CA3 stratum oriens and CA3 stratum radiatum. However, the expression intensity and number of alpha2 positive cells strongly increased to reach peak levels in both cortex and hippocampus at P7 and decreased thereafter to moderate to low to levels. Double in situ hybridization revealed that most, but not all, alpha2 mRNA expression was located in non-pyramidal GAD-positive cortical and hippocampal interneurons. Thus, similar to other nAChR subunits, alpha2 mRNA expression is transiently upregulated during postnatal development and nAChRs containing alpha2 subunits could regulate GABAergic activity during a critical period of network formation.

Quantification of digesta flow into the caeca

1. A caecal intubation technique was developed to determine the amount of digesta that enters the caeca of fed and feed-deprived chickens. 2. Dry matter intakes per day for control and caecostomised chickens were not significantly different. 3. For fed and feed-deprived roosters, water intake was significantly increased by caecostomy in control birds and was significantly increased by feeding. 4. Amount of caecal dry matter excretion was significantly increased by feeding, but no difference in caecal water excretion was observed. 5. The ratio of caecal excretion (caecal/total excretion) of dry matter and water tended to decrease in response to feeding. 6. It is concluded that dry matter entry into the caeca represents 18% or 25% of the total dry matter excretion in fed or feed-deprived birds, respectively. Corresponding values for water entry are 17 and 26%. Therefore, the caeca play an important role in water balance.

Manganese induces endoplasmic reticulum (ER) stress and activates multiple caspases in nigral dopaminergic neuronal cells, SN4741

Chronic exposure to manganese causes Parkinson's disease (PD)-like clinical symptoms (Neurotoxicology 5 (1984) 13; Arch. Neurol. 46 (1989) 1104; Neurology 56 (2001) 4). Occupational exposure to manganese is proposed as a risk factor in specific cases of idiopathic PD (Neurology 56 (2001) 8). We have investigated the mechanism of manganese neurotoxicity in nigral dopaminergic (DA) neurons using the DA cell line, SN4741 (J. Neurosci. 19 (1999) 10). Manganese treatment elicited endoplasmic reticulum (ER) stress responses, such as an increased level of the ER chaperone BiP, and simultaneously activated the ER resident caspase-12. Peak activation of other major initiator caspases-like activities, such as caspase-1, -8 and -9, ensued, resulting in activation of caspase-3-like activity during manganese-induced DA cell death. The neurotoxic cell death induced by manganese was significantly reduced in the Bcl-2-overexpressing DA cell lines. Our findings suggest that manganese-induced neurotoxicity is mediated in part by ER stress and considerably ameliorated by Bcl-2 overexpression in DA cells.

Phenotypic differentiation during migration of dopaminergic progenitor cells to the olfactory bulb

A possible source for transplantable neurons in Parkinson's disease are adult olfactory bulb (OB) dopamine (DA) progenitors that originate in the anterior subventricular zone and reach the OB through the rostral migratory stream. We used adult transgenic mice expressing a lacZ reporter directed by an 8.9 kb tyrosine hydroxylase (TH) promoter to investigate the course of DAergic differentiation. Parallel transgene and intrinsic TH mRNA expression occurred during migration of DA interneurons through the mitral and superficial granule cell layers before these cells reached their final periglomerular position. Differential transgene and calcium-calmodulin-dependent protein kinase IV expression distinguished two nonoverlapping populations of interneurons. Transgenic mice carrying a TH8.9kb/lacZ construct with a mutant AP-1 site demonstrated that this element confers OB DA-specific TH gene regulation. These results indicate that DA phenotypic determination is specific to a subset of mobile OB progenitors.

Effects of caecal ligation and colostomy on water intake and excretion in chickens

1. The effect of caecal ligation and colostomy on water intake and excretion were examined in chickens fed a low-protein diet or a low-protein diet supplemented with urea. 2. When fed a low-protein diet, the water intake and the ratio of water intake to food intake were increased by colostomy (P < 0.05) but not changed further by caecal ligation of colostomised chickens. 3. When fed a low-protein diet supplemented with urea, the amount of water intake and the ratio of water intake to food intake were not changed by either treatment. 4. Total water excretion was much higher in the colostomised plus caeca-ligated chickens than in other 3 groups fed both types of diet (P < 0.05). 5. The amount of faecal water excretion was increased by cecal ligation in colostomised chickens fed either diet (P < 0.01). 6. No effect of any treatment on water balance was observed in chickens fed either diet. 7. It is concluded that the lower intestine plays a useful role in the water economy of chickens fed a low-protein diet or a low-protein diet supplemented with urea.

Dopaminergic cell death induced by MPP(+), oxidant and specific neurotoxicants shares the common molecular mechanism

Recent etiological study in twins (Tanner et al. 1999) strongly suggests that environmental factors play an important role in typical, non-familial Parkinson's disease (PD), beginning after age 50. Epidemiological risk factor analyses of typical PD cases have identified several neurotoxicants, including MPP(+) (the active metabolite of MPTP), paraquat, dieldrin, manganese and salsolinol. Here, we tested the hypothesis that these neurotoxic agents might induce cell death in our nigral dopaminergic cell line, SN4741 (Son et al. 1999) through a common molecular mechanism. Our initial experiments revealed that treatment with both MPP(+) and the other PD-related neurotoxicants induced apoptotic cell death in SN4741 cells, following initial increases of H(2)O(2)-related ROS activity and subsequent activation of JNK1/2 MAP kinases. Moreover, we have demonstrated that during dopaminergic cell death cascades, MPP(+), the neurotoxicants and an oxidant, H(2)O(2) equally induce the ROS-dependent events. Remarkably, the oxidant treatment alone induced similar sequential molecular events: ROS increase, activation of JNK MAP kinases, activation of the PITSLRE kinase, p110, by both Caspase-1 and Caspase-3-like activities and apoptotic cell death. Pharmacological intervention using the combination of the antioxidant Trolox and a pan-caspase inhibitor Boc-(Asp)-fmk (BAF) exerted significant neuroprotection against ROS-induced dopaminergic cell death. Finally, the high throughput cDNA microarray screening using the current model identified downstream response genes, such as heme oxygenase-1, a constituent of Lewy bodies, that can be the useful biomarkers to monitor the pathological conditions of dopaminergic neurons under neurotoxic insult.

The zona pellucida-initiated acrosome reaction: defect due to mutations in the sperm glycine receptor/Cl(-) channel

The mammalian sperm acrosome reaction (AR) is essential to fertilization, and the egg zona pellucida (ZP) is generally believed to be an in vivo initiator of the fertilizing sperm AR. Previously a neuronal glycine receptor/Cl(-) channel (GlyR) was detected on the plasma membrane of mammalian sperm and earlier pharmacological studies suggested that this receptor/channel is important to the ZP-initiated AR. Here, sperm from mice with mutations in the neuronal GlyR alpha or beta subunits (spasmodic and spastic) were shown to be deficient in their ability to undergo the AR initiated in vitro by glycine or by solubilized ZP from mouse eggs. However, both spontaneous and calcium ionophore (A23187)-initiated AR were unaffected. The ZP-initiated AR in wild-type sperm was maximal after 2 h of capacitation, but capacitation of sperm from spasmodic mice for up to 3 h did not result in significant ZP-initiated AR. Similar results were observed when sperm from wild-type and spastic mice were compared. Testis from mice with the beta subunit mutation contained truncated beta subunit mRNAs. Moreover, a monoclonal antibody against GlyR completely blocked ZP initiation of AR in normal mouse sperm. Our results are consistent with an essential role for the sperm GlyR in the ZP-initiated AR.

Effect of caecectomy on growth, moisture in excreta, gastrointestinal passage time and uric acid excretion in growing chicks

1. The effect of caecectomy on nitrogen utilisation and excretion was examined in growing chicks fed on a commercial diet. 2. Caecectomy had no significant effect on food intake or body weight gain. 3. Caecectomy caused significantly higher moisture content in excreta (P<0.01). 4. Gastrointestinal passage time of digesta was significantly shorter in caecectomised chicks than in control chicks (P<0.05). 5. Caecectomy tended to improve nitrogen utilisation rate in growing chicks. 6. The treatment significantly decreased uric acid excretion (P<0.01) and excretory uric acid-N/total nitrogen excretion (P<0.01). 7. It is concluded that the effects of caecectomy on nitrogen metabolism in growing chicks are similar to those in adult chickens.

Effect of removal of caecal contents on nitrogen utilisation and nitrogen excretion in caecally ligated chickens fed on a low protein diet supplemented with urea

1. The effect of washing out the caecal contents on nitrogen utilisation and nitrogen excretion were examined in Single Comb White Leghorn cockerels fed on a 50 g/kg protein diet supplemented with urea. 2. Flushing out the caecal contents with saline in caecally ligated chickens produced a significantly increased nitrogen balance and increased nitrogen utilisation (P<0.05). 3. Washing out the caecal contents significantly decreased uric acid excretion but the treatment had no effect on urea and ammonia excretion. 4. Caecal bacterial contents were significantly decreased by caecal ligation and decreased further by washing out the caecal contents. 5. It is concluded that nitrogen metabolism in chickens is affected by possible changes in caecal fermentation produced by preventing substances from urine and digesta from entering the caeca.

Identification of potential compounds promoting BDNF production in nigral dopaminergic neurons: clinical implication in Parkinson's disease

Parkinson's disease (PD) is characterized by the selective loss of dopamine (DA) neurons in the substantia nigral brain region. Currently, there is no cure or treatment that prevents such neuronal loss. Brain-derived neurotrophic factor (BDNF) has been found to support the survival of DA neurons in animal models and in primary cell cultures. However, the large molecular size of BDNF, coupled with the blood brain barrier, prevents its delivery to DA neurons to promote cell survival in the PD brain. The nigral DA neurons have the ability to produce BDNF for neuroprotection via either autocrine or paracrine mechanisms. Low mol. wt compounds were tested to see whether they could increase the production of BDNF in the DA neurons. The compounds tested include neurotransmitters, neuropeptides, intracellular signaling agents, known neuroprotective agents and growth factors. Our results demonstrate that salicyclic acid, cGMP analog, okadaic acid, IBMX, dipyridamole and glutamate significantly enhance BDNF production in DA neuronal cells.

The mouse sperm glycine receptor/chloride channel: cellular localization and involvement in the acrosome reaction initiated by glycine

Previously, we reported that glycine initiates the in vitro acrosome reaction (AR) of porcine and human sperm by a mechanism that includes the glycine receptor/Cl- channel (GlyR) and that this receptor/channel is required for the zona-pellucida-initiated AR. Because mouse sperm are important tools in the study of fertilization, we investigated whether glycine initiated the mouse sperm AR and whether the sperm GlyR was involved in that initiation. Glycine (250 microM to 1 mM) initiated the AR of capacitated but not noncapacitated mouse sperm. The glycine-initiated AR was significantly inhibited by 50 nM strychnine, a neuronal GlyR antagonist. The neuronal GlyR agonists taurine and beta-alanine did not initiate the AR at 1 mM or 5 mM. A monoclonal antibody against the rat spinal cord GlyR significantly inhibited the glycine-initiated AR but not the spontaneous AR. Indirect immunofluorescence localization studies with that monoclonal antibody and postfixed live sperm detected 3 patterns of immunoreactivity involving 2 sites in the periacrosomal plasma membrane. These patterns were as follows: type A localization on the plasma membrane overlying the tip of the anterior acrosomal region; type B localization on the plasma membrane overlying the posterior part of the acrosomal equatorial segment and/or, in acrosome-reacted sperm, the posterior part of the modified equatorial segment; and type C localization that included both type A and type B. Type A and type C localization were only observed on the acrosome-intact sperm. During capacitation, the number of the sperm showing type A localization increased. Our results demonstrate that mouse sperm provide an excellent model for studying the role of the GlyR in the acrosome reaction.

Altered presynaptic gene expression in transgenic mice producing dopamine in the pineal gland

Neurotransmitters are known to play an important role in the development of the nervous system. We recently generated transgenic mice that ectopically express tyrosine hydroxylase (TH) and thereby produce dopamine (DA) de novo in pinealocytes of the pineal gland (PG). The transgenic PG also exhibited a dramatic decrease in TH-immunoreactive (IR) fibers putatively arising from the superior cervical ganglion (SCG) (Cho et al. [1996] Proc Natl Acad Sci USA 93:2862-2866). In the current study, however, we found that there was no reduction in the number of fibers immunostained for neurofilament protein or PGP9.5, markers known to be heavily localized in fibers, despite the reduction of TH fiber density. Therefore, we investigated whether the decreased TH-IR fiber density is the consequence of reduced sympathetic innervation, or a decrease in TH expression within innervating fibers. Immunohistochemical analysis comparing control and transgenic PG demonstrated no apparent differences in numbers of NPY- and aromatic-L-amino acid decarboxylase (AADC)-IR fibers, indicating that TH expression is decreased in a normal number of innervating fibers. Furthermore, presynaptic neurons in the transgenic SCG showed abnormal and heterogeneous TH immunoreactivity and reduced TH and norepinephrine transporter (NET) mRNA levels. These results show that ectopic DA production in the PG lowers TH and NET gene expression in the SCG without altering sympathetic innervation to the PG and suggest that the alteration of target neurotransmitter phenotype may influence gene expression of phenotype-specific proteins in projecting neurons.

Neuroprotection and neuronal differentiation studies using substantia nigra dopaminergic cells derived from transgenic mouse embryos

The major pathological lesion of Parkinson's disease (PD) is the selective cell death of dopaminergic (DA) neurons in substantia nigra (SN). Although the initial cause and subsequent molecular signaling mechanisms leading to DA cell death underlying the PD process remain elusive, brain-derived neurotrophic factor (BDNF) is thought to exert neuroprotective as well as neurotrophic roles for the survival and differentiation of DA neurons in SN. Addressing molecular mechanisms of BDNF action in both primary embryonic mesencephalic cultures and in vivo animal models has been technically difficult because DA neurons in SN are relatively rare and present with many heterogeneous cell populations in midbrain. We have developed and characterized a DA neuronal cell line of embryonic SN origin that is more accessible to molecular analysis and can be used as an in vitro model system for studying SN DA neurons. A clonal SN DA neuronal progenitor cell line SN4741, arrested at an early DA developmental stage, was established from transgenic mouse embryos containing the targeted expression of the thermolabile SV40Tag in SN DA neurons. The phenotypic and morphological differentiation of the SN4741 cells could be manipulated by environmental cues in vitro. Exogenous BDNF treatment produced significant neuroprotection against 1-methyl-4-phenylpyridinium, glutamate, and nitric oxide-induced neurotoxicity in the SN4741 cells. Simultaneous phosphorylation of receptor tyrosine kinase B accompanied the neuroprotection. This SN DA neuronal cell line provides a unique model system to circumvent the limitations associated with primary mesencephalic cultures for the elucidation of molecular mechanisms of BDNF action on DA neurons of the SN.

Regulation of tyrosine hydroxylase promoter activity by chronic morphine in TH9.0-LacZ transgenic mice

Levels of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, are known to be upregulated in specific brain regions by chronic administration of drugs of abuse. Chronic morphine administration increases TH levels in the locus coeruleus and ventral tegmental area, whereas chronic cocaine administration increases TH levels in the ventral tegmental area only. While such upregulation of TH has been related to behavioral effects of the drugs, the mechanism underlying these adaptations has remained controversial. To study the possibility that upregulation of TH occurs at the transcriptional level, we investigated the effect of chronic morphine or cocaine treatment on the activity of the TH gene promoter (9.0 kb), coupled to the LacZ reporter gene, in transgenic mice. These TH9.0-LacZ mice have been shown to exhibit correct tissue-specific expression and regulation of the reporter gene. We show here that chronic (but not acute) exposure of the TH9.0-LacZ mice to morphine increases the expression of beta-galactosidase (which is encoded by the LacZ gene) in the locus coeruleus by twofold compared with sham-treated mice. In contrast, beta-galactosidase expression in the ventral tegmental area was decreased 20-25% by chronic morphine and unaffected by chronic cocaine administration. Similar results were obtained after analysis of TH mRNA levels in these brain regions by in situ hybridization. These results suggest that chronic morphine upregulates TH expression via transcriptional mechanisms in the locus coeruleus but by post-transcriptional mechanisms in the ventral tegmental area.

Differential expression of monoamine oxidase A, serotonin transporter, tyrosine hydroxylase and norepinephrine transporter mRNA by anorexia mutation and food deprivation

The Anorexia (anx) mutation causes reduced food intake in preweanling mice, resulting in death from starvation within 3-4 weeks. We have found serotonin (5HT) hyperinnervation in the anx brain; altered noradrenergic (NE) innervation may also mediate eating disorders. We examined the expression of synthetic or catabolic monoamine enzyme genes in brainstem nuclei: serotonin transporter (5HTT) and monoamine oxidase A (MAOA) in the raphe nuclei (RN), and MAOA, norepinephrine transporter (NET), and tyrosine hydroxylase (TH) in the locus ceruleus (LC). We compared 3-week old anx with control and 24-h food-deprived wildtype littermates using in situ hybridization to measure mRNA levels by quantitative autoradiography. The anx mutation was correlated with decreased MAOA mRNA in the LC (but not RN), decreased 5HTT mRNA in the RN, and a trend towards lower NET mRNA in the LC. Food deprivation decreased MAOA mRNA in the LC (but not RN), increased TH mRNA in the LC, and did not alter NET or 5HTT mRNA levels. Thus, the effect of the anx mutation on MAOA expression in the LC paralleled the effect of food-deprivation, but the anx mutation and food-deprivation had differential effects on the expression of TH, NET, and 5HTT genes. Decreased 5HTT expression in the anx RN is consistent with upregulation of serotonergic neurotransmission that may accompany 5HT hyperinnervation. Central NE levels or innervation may be altered in anx mice by decreased expression of NET and MAOA and a lack of TH upregulation induced by food deprivation as in wild-type mice.

Neuropeptide Y mRNA and serotonin innervation in the arcuate nucleus of anorexia mutant mice

The anorexia (anx) mutation causes reduced food intake in preweanling mice, resulting in death from starvation within 3-4 weeks. In wild-type rodents, starvation induces increased neuropeptide Y (NPY) mRNA levels in the arcuate nucleus that promotes compensatory hyperphagia. Despite severely decreased body weight and food intake at 3-weeks age, anx/anx mice do not show elevated NPY mRNA levels in the hypothalamic arcuate nucleus compared to wild-type/heterozygous littermates. The NPY mRNA levels can be upregulated in normal mice at this chronological age, because 24-h food deprivation increased arcuate NPY mRNA in wild-type littermates. The unresponsiveness of NPY expression in the arcuate of anx/anx mice was paralleled by serotonergic hyperinnervation of the arcuate nucleus, comparable to the serotonergic hyperinnervation previously reported in the rest of the anx/anx brain. This result is consistent with the hypothesis that wasting disorders are accompanied by disregulation of NPY mRNA expression in the arcuate nucleus, and suggests that reduced food intake, the primary behavioral phenotype of the anx/anx mouse, may be the result of altered hypothalamic mechanisms that normally regulate feeding.

Ligation of caeca improves nitrogen utilisation and decreases urinary uric acid excretion in chickens fed on a low protein diet plus urea

1. The effect of the ligation of the caeca on nitrogen utilisation and nitrogen excretion was examined in conventional chickens fed a diet containing 50 g protein/kg plus urea. 2. Ligation of the caeca significantly improved nitrogen balance and utilisation by up to more than 2 times as much as those of controls (P < 0.05). 3. The treatment significantly decreased uric acid excretion by 77 mg nitrogen/day (P < 0.01) and also total nitrogen excretion (P < 0.05): the former decrease almost explained the latter. 4. No effect of the ligation of caeca on urea and ammonia excretion was observed. 5. It is concluded that nitrogen metabolism in chickens is affected by possible changes in caecal fermentation by preventing entry into the caeca of substances from urine and digesta.

Monitoring catecholamine differentiation in the embryonic brain and peripheral neurons using E. coli lacZ as a reporter gene

An X-gal based histochemical assay was used to detect catecholamine (CA) cells in transgenic mouse embryos, in which the expression of the lacZ reporter was driven by the tissue-specific promoter of the rat tyrosine hydroxylase (TH) gene. As the first enzyme in the biosynthetic pathway for CA neurotransmitters, TH is a specific phenotypic marker for CA cells in the central and peripheral nervous systems of adult animals. During embryogenesis, TH expression appears permanently within CA-producing cells, and transiently within several other cell types. In this study we were able to monitor TH expression in transgenic mouse embryos by following the expression of the lacZ reporter in substantia nigral dopaminergic neurons in the central nervous system, the trigeminal (V) sensory ganglia, and dorsal root ganglia in the periphery. Our results demonstrate that the rat TH promoter-lacZ transgene provides an important experimental tool for monitoring catecholaminergic lineage cells during embryogenesis.

Two distinct P2 purinergic receptors, P2Y and P2U, are coupled to phospholipase C in mouse pineal gland tumor cells

We found that extracellular ATP can increase the intracellular Ca2+ concentration ([Ca2+]i) in mouse pineal gland tumor (PGT-beta) cells. Studies of the [Ca2+]i rise using nucleotides and ATP analogues established the following potency order: ATP, adenosine 5'-O-(3-thiotriphosphate) > or = UTP > 2-chloro-ATP > 3'-O-(4-benzoyl)benzoyl ATP, GTP > or = 2-methylthio ATP, adenosine 5'-O-(2-thiodiphosphate) (ADP beta S) > CTP. AMP, adenosine, alpha,beta-methyleneadenosine 5'-triphosphate, beta,gamma-methyleneadenosine 5'-triphosphate, and UMP had little or no effect on the [Ca2+]i rise. Raising the extracellular Mg2+ concentration to 10 mM decreases the ATP- and UTP-induced [Ca2+]i rise, because the responses depend on the ATP4- and UTP4- concentrations, respectively. The P2U purinoceptor-selective agonist UTP and the P2Y purinoceptor-selective agonist ADP beta S induce inositol 1,4,5-trisphosphate generation in a concentration-dependent manner with maximal effective concentrations of approximately 100 microM. In sequential stimulation, UTP and ADP beta S do not interfere with each other in raising the [Ca2+]i. Costimulation with UTP and ADP beta S results in additive inositol 1,4,5-trisphosphate generation to a similar extent as is achieved with ATP alone. Pretreatment with pertussis toxin inhibits the action of UTP and ATP by maximally 45-55%, whereas it has no effect on the ADP beta S response. Treatment with 1 microM phorbol 12-myristate 13-acetate inhibits the ADP beta S-induced [Ca2+]i rise more effectively than the ATP- and UTP-induced responses. These results suggest that P2U and P2Y purinoceptors coexist on PGT-beta cells and that both receptors are linked to phospholipase C.

Induction of interferon-gamma inducing factor in the adrenal cortex

Interferon-gamma inducing factor (IGIF) is a recently identified cytokine also called interleukin-1gamma (IL-1gamma) or interleukin-18 (IL-18). Its biological activity is pleiotropic, and, so far, it has been shown to induce interferon-gamma production in Th1 cells, to augment the production of granulocyte-macrophage-CSF, and to decrease that of interleukin-10 (IL-10). We first detected newly synthesized IGIF mRNA by differential display in the adrenal gland of reserpine-treated rats and then isolated two transcripts by reverse transcription polymerase chain reaction. They were identified as rat IGIF on the basis of the high homology with mouse: 91% at both the nucleotide and the amino acid level. Subsequently, we investigated the effects of stress on IGIF mRNA levels and found that acute cold stress strongly induced IGIF gene expression. In situ hybridization analysis showed that IGIF is synthesized in the adrenal cortex, specifically in the zona reticularis and fasciculata that produce glucocorticoids. The presence of IGIF mRNA was also detected in the neurohypophysis although induction by stress was not significant. Our results call for more attention to the role of the adrenal gland as a potential effector of immunomodulation and suggest that IGIF itself might be a secreted neuroimmunomodulator and play an important role in orchestrating the immune system following a stressful experience.

Genetically engineered neural transmission

Neural transmission is a communication between neurons and target cells, resulting in behavioral and physiological changes. Defective or altered neural transmission is thought to occur in neuropsychiatric and neurodegenerative illnesses. To probe the biological consequences of defective or altered neural transmission, various genetically engineered transgenic mouse models have been developed, together with conventional pharmacological manipulation. Via genetic manipulation, we are able to engineer specific neurotransmitters, receptors, inactivation of neurotransmitters or neural innervation density. Moreover, recently developed molecular genetic techniques make it possible to induce either a gene knock out event or transgene expression at a discrete time point in a specific neuronal population in both embryos and adult animals. In conjunction with pharmacological manipulation, these sophisticated genetic manipulations of neural transmission will provide new tools to control neural transmission in both normal and pathophysiological conditions.

Prolonged in vivo gene expression driven by a tyrosine hydroxylase promoter in a defective herpes simplex virus amplicon vector

A 9.0-kb fragment of the tyrosine hydroxylase (TH) promoter, previously shown to direct tissue-specific expression in transgenic mice, was fused to an Escherichia coli LacZ reporter gene in a defective herpes simplex virus type-1 (HSV-1) amplicon vector (THlac). The HSV immediate early (IE) 4/5 promoter (HSVlac) was used as a control. LacZ gene expression was visualized by X-Gal histochemical and TH immunocytochemical analysis. Two days and 10 weeks after THlac injection into rat caudate nucleus (CN), X-Gal-stained cells were observed in the substantia nigra (SN) and locus ceruleus (LC) ipsilateral to the injection site. These blue cells were TH-positive neurons as evidenced by double labeling with immunocytochemistry. Moreover, the number of X-Gal+, TH+ (double-positive) neurons in the SN increased at 10 weeks as compared to that seen 2 days after THlac injection. In marked contrast, few double-positive nigral neurons were observed either 2 days or 10 weeks after direct injection of THlac into SN. However, neither nigral nor striatal injection of HSVlac resulted in prolonged gene expression. These results suggest that a neuronal, but not a viral, promoter in an HSV vector can produce cell-type-specific, prolonged, and stable gene expression following retrograde transport. In addition, THlac produced infrequent gene expression in TH-negative cells (CN and dorsal to SN) after THlac injection into CN and SN, respectively. Overall, these results suggest that in some in vivo contexts cell-type-preferred expression can be achieved by a cellular promoter in an amplicon vector. Moreover, they underscore the need for the careful and systematic study of neuronal promoters in HSV vectors.

A transgenic mouse model to study transsynaptic regulation of tyrosine hydroxylase gene expression

Previous studies demonstrated that 9 kb of the rat tyrosine hydroxylase (TH) 5' flanking sequence directed appropriate spatiotemporal expression of a lacZ reporter gene to catecholaminergic cells in the CNS of transgenic mice. In the present study, specificity of transgene expression was further extended to demonstrate cell type-specific functional regulation of lacZ expression using manipulations known to alter endogenous TH expression. Alterations in lacZ reporter expression should parallel changes in endogenous TH levels if the DNA elements mediating these functional changes of TH expression in vivo reside within the 9 kb of the TH promoter region. Naris closure induced an activity-dependent decrease of TH expression in dopaminergic periglomerular cells in the olfactory bulb that was paralleled by down-regulation of lacZ expression in the transgenic mice. Densitometry and image analysis were used to quantify lacZ expression following acute reserpine administration (5 mg/kg s.c.), which up-regulates endogenous TH. At 48 h postinjection, analysis of OD values indicated a significant increase of X-gal staining in the locus coeruleus and ventral tegmental area but not in the substantia nigra or olfactory bulb of reserpine-treated transgenic animals. These data showed that the 9-kb sequence also mediates cell type-specific transsynaptic regulation of reporter gene expression. Analysis of this transgenic animal offers a useful model system to study in vivo regulation of TH gene expression.

Reduced sympathetic innervation after alteration of target cell neurotransmitter phenotype in transgenic mice

Neurotransmitters play a variety of important roles during nervous system development. In the present study, we hypothesized that neurotransmitter phenotype of both projecting and target cells is an important factor for the final synaptic linkage and its specificity. To test this hypothesis, we used transgenic techniques to convert serotonin/melatonin-producing cells of the pineal gland into cells that also produce dopamine and investigated the innervation of the phenotypically altered target cells. This phenotypic alteration markedly reduced the noradrenergic innervation originating from the superior cervical ganglia. Although the mechanism by which the reduction occurs is presently unknown, quantitative enzyme-linked immunoassay showed the presence of the equivalent amounts of nerve growth factor (NGF) in the control and transgenic pineal glands, suggesting that it occurred in a NGF-independent manner. The results suggest that target neurotransmitter phenotype influences the formation of afferent connections during development.

Immortalization of neuroendocrine pinealocytes from transgenic mice by targeted tumorigenesis using the tryptophan hydroxylase promoter

Tryptophan hydroxylase (TPH) is the first enzyme in both serotonin and melatonin biosynthesis in neuroendocrine cells of the pineal gland. The lack of immortalized neuroendocrine pineal cell lines has been a major obstacle to the study of the tissue-specific and circadian regulation of TPH gene expression in the pineal gland. Previously, we demonstrated that a 6.1 kb 5' upstream region of the mouse TPH gene directs the restricted expression of a lacZ reporter gene to the pineal gland and the raphe nuclei of transgenic mice. Therefore, to develop TPH-expressing pineal cell lines we first established transgenic mice carrying a construct consisting of 6.1 kb of 5' flanking region fused to the SV40 T-antigen. These animals developed highly invasive pineal tumors and died at 12-15 weeks of age. The pineal tumors obtained from the transgenic mice were utilized to establish the immortalized pinealocyte-derived cell lines. These cells express two marker enzymes, TPH and serotonin N-acetyltransferase (NAT). In pineal gland TPH and NAT expressions have been known to be regulated during circadian cycle. The two established cell lines therefore promise to be a valuable in vitro model system for the study of the rhythmic nature of the pineal function at molecular level in mammal.

Early ontogeny of catecholaminergic cell lineage in brain and peripheral neurons monitored by tyrosine hydroxylase-lacZ transgene

As the first and rate limiting enzyme in the biosynthetic pathway for catecholamine (CA) neurotransmitters, tyrosine hydroxylase (TH) is a specific phenotypic marker for CA cells in the central and peripheral nervous systems of adult animals. During embryogenesis, TH expression appears permanently within cells destined to be CA-secreting during adult life, and transiently in several cell types that will not express TH in adulthood. In this study, we examined the early ontogeny of TH expression in transgenic mouse embryos by following the expression of a lacZ reporter, driven by the tissue-specific promoter of the rat TH gene. The lacZ reporter product, beta-galactosidase (beta-gal), visualized by X-gal staining, first became apparent in primordia of sensory ganglia serving the glossopharyngeal (IX) and vagal (X) cranial nerves at embryonic day (E)9.0. Between E9.5 and E10.5, beta-gal expression extended to the remaining cranial sensory ganglia serving the trigeminal (V) and facial (VII) nerves, dorsal root ganglia, ventrolateral neural tube and sympathetic ganglion primordia. During that same period, the first beta-gal expression in the embryonic brain also appeared within distinct regions, such as the ventral prosencephalon, the ventral and dorsolateral mesencephalon and the rostral and caudal rhombencephalon. The level of beta-gal expression in all these tissues decreased at E13.5, but a distinct adult pattern of beta-gal expression started to emerge in the substantia nigra and ventral tegmental area in the central nervous system and the adrenal medulla in the periphery. Our findings indicate that the proximal 9.0 kb of the 5' promoter region of the rat TH gene encodes sufficient information to direct development of the appropriate catecholaminergic lineage cells in the central and most peripheral nervous systems during embryogenesis.

Alternate promoters in the rat aromatic L-amino acid decarboxylase gene for neuronal and nonneuronal expression: an in situ hybridization study

Aromatic L-amino acid decarboxylase (AADC) is found in both neuronal cells and nonneuronal cells, and a single gene encodes rat AADC in both neuronal and nonneuronal tissues. However, two cDNAs for this enzyme have been identified: one from the liver and the other from pheochromocytoma. Exons 1a and 1b are found in the liver cDNA and the pheochromocytoma cDNA, respectively. In the third exon (exon 2), there are two alternatively utilized splicing acceptors specific to these exons, 1a and 1b. Structural analysis of the rat AADC gene showed that both alternative promoter usage and alternative splicing are operative for the differential expression of this gene. To demonstrate whether alternative promoter usage and splicing are tissue specific and whether the exons 1a and 1b are differentially and specifically transcribed in nonneuronal and neuronal cells, respectively, in situ hybridization histochemistry for the rat brain, adrenal gland, liver, and kidney was carried out using these two exon probes. The exon 1a probe specifically identified AADC mRNA only in nonneuronal cells, including the liver and kidney, and the exon 1b probe localized AADC mRNA to monoaminergic neurons in the CNS and the adrenal medulla. Thus, both alternative promoter usage and differential splicing are in fact operative for the tissue-specific expression of the rat AADC gene.

5' upstream DNA sequence of the rat tyrosine hydroxylase gene directs high-level and tissue-specific expression to catecholaminergic neurons in the central nervous system of transgenic mice

Tyrosine hydroxylase (TH), the first and rate-limiting enzyme in the biosynthesis of catecholamine neurotransmitters, is expressed within central and peripheral catecholaminergic cells. To delineate DNA sequences necessary for tissue-specific expression of the rat TH gene, transgenic mice were produced containing 0.15 kb, 2.4 kb, and 9.0 kb of 5' flanking sequence fused to the E. coli lacZ (beta-galactosidase) reporter gene. The reporter gene expression in the transgenic animals was monitored by both X-gal histochemical staining and beta-galactosidase immunohistochemistry and compared to TH mRNA and protein expression. Transgenic mice bearing 9.0 kb, but not the smaller constructs with either 2.4 kb or 0.15 kb of 5' flanking sequence, fused to lacZ were able to direct high level expression of beta-galactosidase at levels equivalent to the endogenous TH in central catecholaminergic cells, and to a lesser degree to adrenal gland. Previously, 4.8 kb of 5' flanking region was reported to contain some tissue-specific element(s) determined by chloramphenicol acetyltransferase (CAT) assay using regional brain dissections and was not able to demonstrate cellular localization of the CAT expression [2]. Using histological procedures which allow for spatial resolution, this study demonstrated that the crucial catecholaminergic neuron-specific DNA element(s) resides between -9 kb and -2.4 kb of the 5' flanking region of the rat TH gene; this assertion is substantiated by the high-level of tissue-specific expression of lacZ in catecholaminergic cells.

Drastic and selective hyperinnervation of central serotonergic neurons in a lethal neurodevelopmental mouse mutant, Anorexia (anx)

The autosomal recessive lethal anorexia mutation in mice (anx/anx) causes starvation in preweanlings. In addition, this murine neurodevelopmental mutant shows other distinct phenotypic characteristics and dysfunctional behaviors. Previous studies strongly suggested that the mutation results in elevated serotonergic stimulation, because these traits are characteristic of such overstimulation and because brain serotonin is believed to have an inhibitory effect on feeding behavior. In this report, we show extensive serotonergic hyperinnervation in normal target fields (hippocampus, cortex, olfactory bulb and cerebellum) of mutant mice. Despite the extensive hyperinnervation, the normal laminar organization of the brain was retained. The specificity of the mutation to the serotonergic system was confirmed by demonstration of normal catecholaminergic innervation in the central nervous system (CNS), and this specificity was especially striking in a common target field, the cerebellum. Serotonergic hyperinnervation in these mutant preweanling mice may represent the underlying etiology of increased serotonergic stimulation which leads to anorexic starvation, abnormal behavior, and premature death.

A 6.1 kb 5' upstream region of the mouse tryptophan hydroxylase gene directs expression of E. coli lacZ to major serotonergic brain regions and pineal gland in transgenic mice

Tryptophan hydroxylase (TPH) catalyzes the first step of serotonin biosynthesis in serotonergic neurons and neuroendocrine cells. Serotonin influences diverse vital physiological functions and is thought to play an important role in several human psychiatric disorders. To localize DNA element(s) important for serotonergic tissue-specific expression of TPH, 6.1 kb of the 5' flanking region of the mouse TPH gene was fused to the coding region of the E. coli lacZ gene, and expression of the resulting fusion gene was analyzed in transgenic mice. The 6.1 kb of 5' flanking sequence was able to direct the expression of a lacZ reporter gene to serotonergic tissues in six lines of transgenic mice. A high level of lacZ expression in transgenic mice carrying the fusion gene was detected in the pineal gland as well as a moderate level of lacZ expression in serotonergic brain regions such as the median and dorsal raphe nuclei, the nuclei raphe magnus and raphe pallidus. In contrast, a smaller 5' flanking sequence of 1.1 kb directed no detectable serotonergic tissue-specific lacZ expression in five lines of transgenic mice. These results presented in this paper suggest first that DNA elements critical to serotonergic tissue-specific expression reside between -6.1 kb and -1.1 kb of 5' flanking region of the mouse TPH gene, but second that this region confers a restricted tissue-specific expression.