Behavioural abnormalities in male mice lacking neuronal nitric oxide synthase

Changes in NMDA receptor/nitric oxide signaling pathway in the brain with aging

The N-methyl-D-aspartate (NMDA) receptor/nitric oxide (NO) signaling pathway plays an important role in neuronal plasticity. Previous studies with in vitro autoradiography showed that the number of NMDA receptor/ion channel complexes in the cerebral cortex and hippocampus is decreased by aging. Confocal laser scanning microscopy reveals circuit-specific alterations of NMDA receptor subunit 1 in the dentate gyrus of aged monkeys. Histochemistry for NADPH diaphorase (NADPH-d), a marker for neurons containing NO synthase (NOS), reveals that the number of NADPH-d-positive neurons in the cerebral cortex and striatum is significantly reduced from that in young rats. In the hippocampus, no age-related changes in NADPH-d staining are reported, while in situ hybridization histochemistry indicates an increase in the level of mRNA for neuronal NOS. NOS activity in the brain also appears to decrease with aging. These results suggest that the function of the NMDA receptor/NO signaling pathway in the brain is impaired by aging, and that dysfunction of this signaling pathway may underlie aging-associated memory impairment in rats.

Nitric oxide and endothelin-1 in pulmonary hypertension

BACKGROUND

We have shown previously increased expression of the potent vasoconstrictor peptide endothelin-1 (ET-1) in the pulmonary arteries of patients with pulmonary hypertension. We also demonstrated diminished expression of endothelial nitric oxide synthase, the enzyme responsible for generating nitric oxide (NO), in patients with the same disease.

STUDY OBJECTIVE

To determine the expression of neuronal nitric oxide synthase (NOS-I) and endothelin-converting enzyme-1 (ECE-1) in lungs of patients with pulmonary hypertension.

METHODS

Immunohistochemistry with avidin-biotin-peroxidase method.

RESULTS

There was little immunostaining for NOS-I in the pulmonary arteries of normal control or diseased lungs. Moderate diffuse staining was seen in the airway epithelium and nerve bundles. Immunoreactivity for ECE-1 was seen in the airway epithelium, smooth muscle cells, and scattered macrophages of both normal and diseased lungs. Strong immunoreactivity for ECE-1 was seen in the endothelium of diseased pulmonary arteries of patients with pulmonary hypertension.

CONCLUSION

We conclude that expression of NOS-I appears to be similar in normal and diseased lungs, while abundant expression of ECE-1 is present in diseased vessels, which may contribute to the pathogenesis of arteriopathy in pulmonary hypertension.

Novel strategies to probe the functions of serotonin receptors

Gene targeting has proven to be extremely powerful in various fields of biological research. Through this technique, knockout mice lacking a particular gene, and thus a particular protein, can be generated. One limitation to this technique is the fact that mice develop without the protein of interest and therefore, developmental compensations may have taken place, contributing to an observed phenotype. Inducible strategies, those which allow the timing of expression of a gene to be regulated, are currently being developed and should prove useful when applied to gene targeting technology. To begin to apply such new technologies to the field of gene targeting, we first created and tested several reporter constructions using the tetracycline inducible system. Here we describe the creation of several beta-galactosidase reporter constructions and the results of in vitro testing in Cos-7 cells. We then discuss future knockout strategies based upon our observations.

Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).

Central regulation of autonomic function: no brakes?

1. Nitric oxide (NO) is formed by neuronal NO synthase (nNOS) and acts as a non-conventional neurotransmitter in the brain. A growing body of evidence supports the hypothesis that NO acts to decrease sympathetic output to the periphery; these effects may occur at several autonomic sites. The present review describes studies from our laboratory that address this hypothesis. 2. Restraint stress activates putative NO-producing neurons in many autonomic centres: preoptic area, medial septum, amygdala, hypothalamus, including the paraventricular nucleus (PVN), raphe nuclei, nucleus tractus solitarius (NTS) and ventrolateral medulla (VLM). These results suggest that NO is directly or indirectly involved in regulating sympathetic output to the periphery. 3. Systemic angiotensin II (AngII) activates putative NO-producing neurons in the PVN. These neurons may be activated either by the increases in arterial pressure that accompany AngII injections or due to activation of AngII-containing neural pathways. 4. Hypotension is associated with the activation of putative NO-producing PVN neurons, small numbers of which also project to the NTS or VLM. As the majority of activated neurons is in the magnocellular division, NO production may be related to the production of vasopressin. 5. Adult spontaneously hypertensive rats (SHR) show increased gene expression of nNOS in the hypothalamus, dorsal medulla and caudal VLM. These differences are not present in young prehypertensive SHR, suggesting that the changes in gene expression in adult rats are associated with the increased sympathetic nerve activity found in these rats. 6. Gene expression of nNOS is altered in the hypothalamus and caudal VLM of renal hypertensive rats at 3 and 6 weeks after surgical induction of hypertension. Contrasting results at the two time points may be due to differing underlying physiological processes that characterize the two stages of renal hypertension. 7. Nitric oxide may affect sympathetic output through several possible mechanisms. These include affecting production of the second messenger cGMP and interactions with more classical neurotransmitters or with neurohormonal systems in the brain.

Light and electron microscopic study of neuronal nitric oxide synthase-immunoreactive neurons in the rat subiculum

Neurons in the rat subiculum that are capable of producing nitric oxide were studied by using an antibody to the neuronal isoform of nitric oxide synthase (nNOS). In the light microscope, the staining pattern with the nNOS antibody closely resembled that seen following histochemical processing with nicotinamide adenine dinucleotide phosphate diaphorase. Immunostained neurons were found in all layers, and, in addition, large dendrites in the apical dendrite layer were also immunopositive. Although a few immunolabelled cells had the typical morphology of interneurons, most were found to have the characteristics of pyramidal neurons. In the subiculum, these immunoreactive pyramidal neurons were concentrated mainly in the most superficial cell layers and closest to the CA1 region, but pyramidal neurons in the CA1 layer of the hippocampus were consistently immunonegative. Immunopositive profiles in the subiculum were studied in the electron microscope and compared with unlabelled structures. Ultrastructural criteria suggest that both pyramidal and nonpyramidal subicular neurons are immunopositive for nNOS. Large, spiny dendrites and smaller, varicose dendrites were found to be immunoreactive for nNOS. Vesicle-containing profiles were probably presynaptic axons, and immunopositive boutons were seen to make symmetrical and asymmetrical synaptic contacts.

Behavior in mice with targeted disruption of single genes

The use of mice with targeted deletion, or knockout, of specific genes provides a relatively new approach to establish the molecular bases of behavior. As with all ablation studies, the interpretation of behavioral data may be limited by the technique. For example, indirect effects of the missing gene may affect behavior, rather than the missing gene per se. Also, because the missing gene might affect many developmental processes throughout ontogeny and because up-regulation or compensatory mechanisms may be activated in knockouts, behavioral data from mice with targeted gene deletions should be interpreted with caution. The development of conditional knockouts, in which a specific gene can be inactivated any time during ontogeny, should allow investigators to avoid these conceptual shortcomings associated with behavioral data from knockouts in the near future. The behavioral alterations reported in knockout mice are reviewed here. Many dramatic changes in complex motivated behaviors including aggression, sexual, ingestive, and parental behaviors, have been reported for knockouts. There have also been many reports of alterations in sensorimotor abilities and spontaneous activity, as well as impairments in balance, coordination, and gait. Impaired learning and memory have also been reported for mice with targeted disruption of specific genes. Taken together, the use of knockouts will provide an important new tool to understand the mechanisms underlying behavior.

Adrenergic alpha2C-receptors modulate the acoustic startle reflex, prepulse inhibition, and aggression in mice

Studies on animal models of stress, anxiety, aggression, and sensorimotor gating have linked specific monoamine neurotransmitter abnormalities to the cognitive and behavioral disturbances associated with many affective neuropsychiatric disorders. Although alpha2-adrenoceptors (alpha2-ARs) have been suggested to have a modulatory role in these disorders, the specific roles of each alpha2-AR subtype (alpha2A, alpha2B, and alpha2C) are largely unknown. The restricted availability of relevant animal models and the lack of subtype-selective alpha2-AR drugs have precluded detailed studies in this area. Therefore, transgenic mice were used to study the possible role of the alpha2C-AR subtype in two well established behavioral paradigms: prepulse inhibition (PPI) of the startle reflex and isolation-induced aggression. The alpha2C-AR-altered mice appear grossly normal, but subtle changes have been observed in their brain dopamine (DA) and serotonin (5-HT) metabolism. In this study, the mice with targeted inactivation of the gene encoding alpha2C-ARs (alpha2C-KO) had enhanced startle responses, diminished PPI, and shortened attack latency in the isolation-aggression test, whereas tissue-specific overexpression of alpha2C-ARs (alpha2C-OE) was associated with opposite effects. Correlation analyses suggested that both the magnitude of the startle response and its relative PPI (PPI%) were modulated by the mutations. In addition, the differences in PPI, observed between drug-naive alpha2C-OE mice and their wild-type controls, were abolished by treatment with a subtype nonselective alpha2-agonist and antagonist. Thus, drugs acting via alpha2C-ARs might have therapeutic value in disorders associated with enhanced startle responses and sensorimotor gating deficits, such as schizophrenia, attention deficit disorder, post-traumatic stress disorder, and drug withdrawal.

The gene encoding a cationic amino acid transporter (SLC7A4) maps to the region deleted in the velocardiofacial syndrome

By screening an expressed sequence tag database, we identified a novel human gene, SLC7A4, encoding a solute carrier family 7 [cationic amino acid (CAA) CAT-4 transporter, y+ system] member 4. The SLC7A4 cDNA is 2325 nt long and includes 78, 1911, and 336 nt in the 5' noncoding, coding, and 3'-noncoding regions, respectively. SLC7A4 displays high homology with SLC7A1 and SLC7A2, two previously known CAA transporters. By chromosomal in situ hybridization and YAC identification, SLC7A4 was mapped to 22q11.2, the commonly deleted region of the velocardiofacial syndrome (VCFS, Shprintzen syndrome). In a patient affected by VCFS, deletion of SLC7A4 was demonstrated by chromosomal FISH. By Northern analysis, an abundant transcript was detected in brain, testis, and placenta. Microinjection of SLC7A4 mRNA into Xenopus laevis oocytes demonstrates a significant stimulation of CAA transport.

From Genetically Altered Mice to Integrative Physiology

Transgenic and gene-targeted mice permit the study of the function(s) of the single gene(s) in a whole organism, thereby relating molecular biology and integrative physiology. To demonstrate the potential of transgenic models, we present in this review some physiologically relevant information obtained from genetically engineered mice.

Gene disruption in mice: models of development and disease

Gene targeting technology in mice by homologous recombination has become an important method to generate loss-of-function of genes in a predetermined locus. Although the inactivation is limited to irreversible alteration of chromosomal DNA and a surprising variety of genes have given unexpected and disappointing results, modification of the basic technology now provides additional choices for a more specific and variety of manipulations of the mouse genome. This includes conditional cell-type specific gene targeting, knockin technique and the induction of the specific balanced chromosomal translocations. In the past decade this technique not only generated a wealth of knowledge concerning the roles of growth factors, oncogenes, hormone receptors and Hox genes but also helped to produce animal models for several human genetic disorders. In the future it may provide more powerful and necessary tools to dissect the psychiatric disorders, understanding the complex central nervous system and to correct the inherited disorders.

Schizophrenia: the illness that made us human

Any hypotheses concerning the origins of humans must explain many things. Among these are: 1, the growth in brain size around two million years ago; 2, the presence of subcutaneous fat; 3, the near absence of change or cultural progress for around 2 million years after the brain grew in size; 4, the cultural explosion which began somewhere between fifty thousand and one hundred thousand years ago with the emergence of art, music, religion and warfare; 5, the further cultural explosion around ten thousand to fifteen thousand years ago which developed with the emergence of agriculture and which has continued since. Since the brain, like subcutaneous fat, is particularly rich in lipids, and since the microconnections of the brain are substantially lipid in nature, it is suggested that changes in lipid metabolism are what differentiated humans from the great apes. The growth in brain size and in the quality of subcutaneous adipose tissue may have occurred because of changes in the proteins which regulate the rate of delivery of fatty acids to tissues, notably lipoprotein lipases and fatty acid binding proteins. The creativity which occurred one hundred thousand years ago may have resulted from changes in phospholipid-synthesizing, -remodelling and -degrading enzymes which largely determine the microconnectivity of neurons. Family studies and adoption studies indicate that schizophrenia in a family member is associated with an increased risk of the illness in other family members. It is also associated with an increased risk of schizotypy, manic-depression, dyslexia, sociopathy and psychopathy. On the other hand it is also an indication of an increased likelihood of high creativity, leadership qualities, achievements in many fields, high musical skills and an intense interest in religion. I propose that the characteristics which entered the human race about one hundred thousand years ago and which ended around two million years of cultural near-stagnation are precisely those shown by the families of people with schizophrenia. I propose that these features are caused by variations in phospholipid biochemistry which are responsible both for schizophrenia and for our humanity. This would help to explain why schizophrenia is present to approximately the same degree in all races. It is the illness which made us human prior to the separation of the races.

Nitric Oxide: Diverse Actions in the Central and Peripheral Nervous Systems

Nitric oxide (NO) has revolutionized our conceptions about neurotransmission. NO is not stored in synaptic vesicles, is not released by exocytosis, and does not mediate its action by binding to cell surface receptors. Instead, NO simply diffuses to its targets, and its actions are mediated through molecules that accept or share its unpaired electron. NO has diverse biological roles, including functions as the nitrergic transmitter of the peripheral nervous system, the major regulator of blood vessel tone, and actions as the cytotoxic agent of activated macrophages. In the CNS, NO function is just beginning to be explored, but it seems to play prominent roles in plasticity and the regulation of complex behaviors. Under conditions of excessive formation. NO has emerged as an important endogenous neurotoxin. Strategies aimed at reducing NO formation may therefore have therapeutic benefit. NEUROSCIENTIST 4:96–112, 1998

Modulation of guinea-pig cardiac L-type calcium current by nitric oxide synthase inhibitors

1. Electrophysiological (whole-cell clamp) techniques were used to study the effect of NO synthase (NOS) inhibitors on guinea-pig ventricular calcium current (ICa), and biochemical measurements (Western blot and citrulline synthesis) were made to investigate the possible mechanisms of action. 2. The two NOS inhibitors, NG-monomethyl-L-arginine (L-NMMA, 1 mM) and NG-nitro-L-arginine (L-NNA, 1 mM), induced a rapid increase in ICa when applied to the external solution. D-NMMA (1 mM), the stereoisomer of L-NMMA, which has no effect on NOS, did not enhance ICa. 3. Western blot experiments gave no indication of the presence of inducible NOS protein (iNOS) in our cell preparation, neither immediately after dissociation nor after more than 24 h. Statistically, there was no significant difference between electrophysiological experiments performed on freshly dissociated cells and experiments performed the next day. Moreover cells prepared and kept in the presence of dexamethasone (3 microM), to inhibit the expression of iNOS, gave the same response to L-NMMA as control cells. 4. The stimulatory effect of L-NMMA (1 mM) on basal ICa was reversed by competition with higher doses (5 mM) of externally applied L-arginine, the natural substrate of NOS. The effect of L-NMMA was also eliminated by L-arginine in the patch pipette solution. 5. Intracellular perfusion with GDP beta S (0.5 mM), which stabilizes the G-proteins in the inactive state, did not affect the L-NMMA-induced stimulation of ICa. 6. Carbachol (1 microM) reduced the ICa previously stimulated by L-NMMA, and intracellular cGMP (10 microM) prevented L-NMMA enhancement. 7. Simultaneous treatment with L-NMMA and isoprenaline (1 microM) induced a non-cumulative enhancement of ICa that could not be reversed by carbachol (1 microM). 8. NO synthesis, measured by the formation of [3H]citrulline from L-[3H]arginine during a 15 min incubation, showed a relatively high basal NO production, which was inhibited by L-NMMA but not affected by carbachol. 9. These results suggest that inhibitors of NOS are able to modulate the basal ventricular ICa in the absence of a receptor-mediated pathway, and that NO might be required for the muscarinic reduction of ICa under isoprenaline stimulation, even if NO production is not directly controlled by the muscarinic pathway.

Effects of tamoxifen on nitric oxide synthesis and neoplastic transformation in C3H 10T1/2 fibroblasts

Tamoxifen (TAM) is used in the prevention and treatment of breast cancer, however, its mechanisms of therapeutic action as well as its pathologic effects are not fully understood. We report that TAM (10(-7)-10(-5) M) inhibits 3-methylcholanthrene-induced transformation of C3H 10T1/2 murine fibroblasts in a dose-responsive manner. Over this concentration range, TAM (>10(-6) M) potentiates inducible nitric oxide synthase (iNOS) activity in 10T1/2 cells. This increase in NO synthase activity was mediated through an increase in iNOS protein for cells stimulated with interferon-gamma (IFN-gamma) and bacterial lipopolysaccharide (LPS). Significant increases in NO formation were observed when TAM (10(-5)) was added prior to or simultaneously with IFN-gamma/LPS treatment, whereas the addition of TAM 48 h after IFN-gamma/LPS treatment had no effect on NO synthesis. The morphologic changes seen with cells treated with TAM are similar to those observed in cells treated with TGF-beta1. TGF-beta1 inhibited NO production at high doses and slightly enhanced NO formation at low doses in IFN-gamma/LPS-stimulated cells. The transformation inhibitory effects of TAM did not appear to be related to the effects on cellular proliferation of neoplastic cells as TAM did not inhibit the growth of neoplastic cells into foci in the presence of normal confluent C3H 10T1/2 fibroblasts.

Precise distribution of neuronal nitric oxide synthase mRNA in the rat brain revealed by non-radioisotopic in situ hybridization

Regional distribution of neurons expressing neuronal nitric oxide synthase mRNA in the rat brain was examined by non-radioisotopic in situ hybridization, using digoxigenin-labeled complementary RNA probes. Clustering of intensely positive neurons was observed in discrete areas including the main and accessory olfactory bulbs, the islands of Calleja, the amygdala, the paraventricular nucleus of the thalamus, several hypothalamic nuclei, the lateral geniculate nucleus, the magnocellular nucleus of the posterior commissure, the superior and inferior colliculi, the laterodorsal and pedunculopontine tegmental nuclei, the nucleus of the trapezoid body, the nucleus of the solitary tract and the cerebellum. Strongly-stained isolated neurons were scattered mainly in the cerebral cortex, the basal ganglia and the brain stem, especially the medulla reticular formation. In the hippocampus, an almost uniform distribution of moderately stained neurons was observed in the granular cell layer of the dentate gyrus and in the pyramidal cell layer of the Ammon's horn, while more intensely stained isolated neurons were scattered over the entire hippocampal region. These observations can serve as a good basis for studies on function and gene regulation of neuronal nitric oxide synthase.

Ejaculatory abnormalities in mice with targeted disruption of the gene for heme oxygenase-2

Nitric oxide (NO) is well established as a neurotransmitter in the central and peripheral nervous systems. More recently, another gas, carbon monoxide (CO) has also been implicated in neurotransmission. In the nervous system CO is formed by a subtype of heme oxygenase (HO) designated HO2. HO2 is localized to discrete neuronal populations in the brain resembling localizations of soluble guanylyl cyclase, which is activated by CO. CO may also function in the peripheral autonomic nervous system, in conjunction with NO. The majority of ganglia in the myenteric plexus possess both HO2 and neuronal NO synthase (NOS). Defects in myenteric plexus neurotransmission occur both in mice with targeted deletion of genes for HO2 and neuronal NOS. HO2 also occurs in other autonomic ganglia including the petrosal, superior cervical and nodose ganglia. Neuronal NOS is localized to neurons regulating male reproductive behavior, such as penile erection, and NOS inhibitors prevent erection. Because of the other parallels between NO and CO, we speculated that CO may play a role in male reproductive behavior. In the present study we describe HO2 localization in neuronal structures regulating copulatory reflexes. Reflex activity of the bulbospongiosus muscle, which mediates ejaculation and ejaculatory behavior, is markedly diminished in mice with targeted deletion of the gene for HO2 (HO2-).

Effect of the nitric oxide level in the medial preoptic area on male copulatory behavior in rats

We investigated the influence of the extracellular nitric oxide (NO) level on male copulatory behavior. We confirmed the changes of nitrite (NO2-) and nitrate (NO3-) in the medial preoptic area (MPOA) by administration of the NO precursor L-arginine (L-Arg, 10 mM) or the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 10 mM) via a dialysis probe. NO2- and NO3- were measured simultaneously by an in vivo microdialysis method coupled with the Griess reaction. L-Arg induced significant elevations of extracellular NO2- and NO3-. L-NMMA significantly reduced NO2- and NO3- levels. We observed male copulatory behavior during infusion of L-Arg or L-NMMA. The mount rate of male rats significantly increased during infusion of L-Arg in the MPOA. Administration of L-NMMA reduced the mount rate. These findings suggested that the elevation of extracellular NO in the MPOA facilitates male copulatory behavior of rats, whereas the decrease of NO reduces their copulatory behavior.

An evaluation of what the mouse knockout experiments are telling us about mammalian behaviour

The early gene knockout studies with a neurobiological focus were directed at fairly obvious target genes and added very little to our knowledge of behavioural neuroscience. On the contrary, since the behavioural consequences were often predictable, this helped confirm that the technology was working. However, a substantial number of knockouts of genes expressed in the brain have been without obvious behavioural consequences, supporting the concept of genetic canalisation and redundancy. Others have produced a behavioural deficit for which there is no obvious explanation. Many cells of different tissue types have a capacity for memory, and in the brain, cells of the hippocampus are important for spatial learning and memory. Deleting genes that are expressed in the hippocampus has received considerable attention in this behavioural context. Although the initial studies experienced problems of interpretation, considerable advances have since been made. Knockout mice are now subject to tests of different forms of learning, multicellular hippocampal recordings, and restricted gene deletion specific to cells of component regions. This multi-level approach is proving more informative. Nevertheless, there is still a need to recognise that behavioural expression is several steps removed from gene expression, and that the relationship between genes and behaviour can be reciprocal.

Serotonin, social status and aggression

Serotonin, social status and aggression appear to be linked in many animal species, including humans. The linkages are complex, and, for the most part, details relating the amine to the behavior remain obscure. During the past year, important advances have been made in a crustacean model system relating serotonin and aggression. The findings include the demonstration that serotonin injections will cause transient reversals in the unwillingness of subordinate animals to engage in agonistic encounters, and that at specific synaptic sites involved in activation of escape behavior, the direction of the modulation by serotonin depends on the social status of the animal.

Neuronal adaptations to changes in the social dominance status of crayfish

The effect of superfused serotonin (5-HT; 50 microns) on the synaptic responses of the lateral giant (LG) interneuron in crayfish was found to depend on the social status of the animal. In socially isolated animals. 5-HT persistently increased the response of LG to sensory nerve shock. After social isolates were paired in a small cage, they fought and determined their dominant and subordinate status. After 12 d of pairing, 5-HT reversibly inhibited the response of LG in the social subordinate and reversibly increased the response of LG in the social dominant crayfish. The effect of 5-HT changed approximately linearly from response enhancement to inhibition in the new subordinate over the 12 d of pairing. If, after 12 d pairing, the subordinate was reisolated for 8 d, the response enhancement was restored. If the subordinate, instead, was paired with another subordinate and became dominant in this new pair, the inhibitory effect of 5-HT changed to an enhancing effect over the next 12 d of pairing. If, however, two dominant crayfish were paired and one became subordinate, the enhancing effect of 5-HT persisted in the new subordinate even after 38 d pairing. These different effects of serotonin result from the action of two or more molecular receptors for serotonin. A vertebrate 5-HT, agonist had no effect on social isolates but reversibly inhibited the response of LG in both dominant and subordinate crayfish. The inhibitory effects of the agonist developed approximately linearly over the first 12 d of pairing. A vertebrate 5-HT2 agonist persistently increased the response of LG in isolate crayfish and reversibly increased the response of the cell in dominant and subordinate crayfish. Finally, although neurons that might mediate these effects of superfused 5-HT are unknown, one pair of 5-HT-immunoreactive neurons appears to contact the LG axon and initial axon segment in each abdominal ganglion in its projection caudally from the thorax.

Cyclic guanosine 3',5'-monophosphate-mediated neuroprotection by nitric oxide in dissociated cultures of rat dorsal root ganglion neurones

In dissociated cultures of dorsal root ganglia (DRG) derived from 15-day-old rats, many neurones expressed nitric oxide synthase (NOS) and this expression was found to be reduced by nerve growth factor. The application of blockers of NOS caused selective death of those neurones expressing NOS. The soluble guanylate cyclase (sGC) blocker ODQ also caused neuronal death. The appearance of the neurones undergoing cell death was typical of apoptosis. This suggests that NO has a neuroprotective action in DRG neurones which is probably mediated by its activation of cyclic guanosine 3',5'-monophosphate. These observations are discussed in relation to the developmental and neuropathic changes in NOS expression by DRG neurones.

Effects of nitric oxide on neuroendocrine function and behavior

Nitric oxide (NO) is an unusual chemical messenger. NO mediates blood vessel relaxation when produced by endothelial cells. When produced by macrophages, NO contributes to the cytotoxic function of these immune cells. NO also functions as a neurotransmitter and neuromodulator in the central and peripheral nervous systems. The effects on blood vessel tone and neuronal function form the basis for an important role of NO on neuroendocrine function and behavior. NO mediates hypothalamic portal blood flow and, thus, affects oxytocin and vasopression secretion; furthermore, NO mediates neuroendocrine function in the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-adrenal axes. NO influences several motivated behaviors including sexual, aggressive, and ingestive behaviors. Learning and memory are also influenced by NO. Taken together, NO is emerging as an important chemical mediator of neuroendocrine function and behavior.

Aggressive behavior in male mice lacking the gene for neuronal nitric oxide synthase requires testosterone

Nitric oxide acts as a neural messenger in both the central and peripheral nervous systems. Mice with targeted disruption of the neuronal isoform of nitric oxide synthase (nNOS - / -) are extremely aggressive relative to wild-type (WT) mice. Male nNOS - / - mice exhibit an increase in the number and duration of aggressive encounters compared to WT animals when tested in a variety of paradigms used to test rodent aggression. This inappropriate aggressive behavior has only been observed in male nNOS - /- mice; nNOS - /- females, like female WT mice, exhibit little or no aggression. The present study sought to test the dependence of increased aggressive behavior in nNOS - / - males on testosterone. Intact nNOS - / - males exhibited elevated levels of aggression relative to intact WT males. Castration reduced aggression in both WT and nNOS - /- males to equivalent low levels. Testosterone replacement restored aggression to precastration levels in both genotypes. These data provide evidence that increased aggressive behavior of nNOS - /- mice, like aggression in WT mice, is testosterone-dependent.

Increased gene expression of neuronal nitric oxide synthase in brain of adult spontaneously hypertensive rats

Neuronal nitric oxide is hypothesized to participate in regulation of autonomic function by decreasing sympathetic output to the periphery. This hypothesis predicts that gene expression of neuronal nitric oxide synthase is increased during states of heightened sympathetic activity. To test the hypothesis, we measured gene expression in the spontaneously hypertensive rat (SHR), a genetic model of hypertension in which sympathetic activity is correlated with increasing pressure. SHRs and two strains of control rats (Wistar-Kyoto [WKY] and Sprague-Dawley [SD]) at 4 weeks (pre-hypertensive) and 14 weeks (established hypertension) of age were used to measure gene expression in hypothalamus, dorsal pons, dorsal medulla, rostral ventrolateral medulla, and caudal ventrolateral medulla. Semi-quantitative reverse transcription-polymerase chain reactions and in situ hybridization were used to measure changes in neuronal nitric oxide synthase mRNA. No significant differences were found in any of the areas studied among the three strains of rats in the 4-week rats. At 14 weeks significant increases in gene expression were found in the hypothalamus (73% compared to WKYs, 104% compared to SDs), dorsal medulla (31% and 45%), and caudal ventrolateral medulla (24% and 27%) of SHRs. In situ hybridization revealed that neurons expressing the synthase gene in the hypothalamus were found primarily in the paraventricular (both parvo- and magnocellular divisions) and supraoptic nuclei. These data show that gene expression of neuronal nitric oxide synthase is increased in central autonomic centers in animals with increased sympathetic activity and they support the hypothesis that nitric oxide plays an important role in maintenance of homeostatic balance through modulation of sympathetic activity.

Transgenic Mouse Models: New Tools for Psychiatric Research

The revolution in molecular genetics promises to identify genes that are responsible for susceptibility to psychopathology and to clarify how genes interact with environmental factors. To date, most studies reporting abnormal behavior have disrupted one specific gene and examined changes in emotionality, cognition, and consumption of food or addictive drugs. Although relating the absence of the product of a deleted gene to a specific behavior is tempting, more refined analysis has shown that the phenotype of a mutant may be a combination of a lacking gene product and the organism's attempt to compensate for the loss. Thus, an absent behavioral phenotype in a mouse with targeted gene disruption does not necessarily indicate the irrelevance of a gene product for behavior, and, vice versa, a specific behavioral abnormality in a mutant does not allow for attribution of this alteration to the lacking gene product. With these limitations in mind, it becomes clear that psychiatric research can expect major profit from the more recently developed gene technologies. The possibility of directing a mutation to specific cell types and sites in the CNS avoids the confounds imposed by changed gene function throughout the body. With few exceptions, psychiatric disorders precipitate in adulthood; thus, an animal model is preferred where the gene under study can be site-specifically turned on or off by a drug-driven “genetic switch.” Recent developments suggest that such tempting research tools will become available in the near future. NEUROSCIENTIST 3:328–336, 1997

Nitric oxide in renal health and disease

Nitric oxide (NO) is a labile radical gas that is widely acclaimed as one of the most important molecules in biology. Through covalent modifications of target proteins and redox reactions with oxygen and superoxide radical and transition metal prosthetic groups, NO plays a critical role in many vital biological processes, including the control of vascular tone, neurotransmission, ventilation, hormone secretion, inflammation, and immunity. Moreover, NO has been shown to influence a host of fundamental cellular functions, such as RNA synthesis, mitochondrial respiration, glycolysis, and iron metabolism. NO is formed from L-arginine by NO synthases (NOSs), a family of related enzymes encoded by separate unlinked genes. The different NOS isozymes exhibit disparate tissue and intrarenal distributions and are governed by unique regulatory mechanisms. In the kidney, NO participates in several vital processes, including the regulation of glomerular and medullary hemodynamics, the tubuloglomerular feedback response, renin release, and the extracellular fluid volume. While NO serves beneficial roles as a messenger and host defense molecule, excessive NO production can be cytotoxic, the result of NO's reaction with reactive oxygen and nitrogen species, leading to peroxynitrite anion formation, protein tyrosine nitration, and hydroxyl radical production. Indeed, NO may contribute to the evolution of several commonly encountered renal diseases, including immune-mediated glomerulonephritis, postischemic renal failure, radiocontrast nephropathy, obstructive nephropathy, and acute and chronic renal allograft rejection. Moreover, impaired NO production has been implicated in the pathogenesis of volume-dependent hypertension. This duality of NO's beneficial and detrimental effects has created extraordinary interest in this molecule and the need for a detailed understanding of NO biosynthesis.

Nitric oxide and apoptosis: another paradigm for the double-edged role of nitric oxide

Apoptosis plays an important role in the development of the organism but also under various pathological conditions. Nitric oxide exhibits contradictory effects in the regulation of apoptosis. Both pro- and antiapoptotic effects have been demonstrated. The proapoptotic effects seem to be linked to pathophysiological conditions, where high amounts of NO are produced by the inducible nitric oxide synthase. In contrast, the continuous release of endothelial NO inhibits apoptosis and may contribute to the antiatherosclerotic function of NO. The present article summarizes these effects and provides insights into the role of NO in apoptotic signal transduction, with special regard to the Bcl-2 homologous proteins, the protease family of caspases and heat shock proteins.

Role of nitric oxide and serotonin in modulation of the cardiovascular defence response evoked by stimulation in the periaqueductal grey matter in rats

In rats anaesthetised with alphaxalone/alphadolone, electrical stimulation (10 s trains of 1 ms pulses at 80 Hz, 40-80 microA) in the dorsolateral and lateral periaqueductal grey matter (PAG), the midbrain defence area, evoked a pressor response with tachycardia and vasodilatation in the hindlimb. Microinjection of 200 nl 0.66 mM 5HT, but not 200 nl 165 mM NaCl, at the site of stimulation attenuated the components of the PAG-evoked response by 75-98%. The effect of 5HT was significantly reduced by prior intracerebroventricular injection of 100 microg N-nitro-L-arginine methyl ester (an inhibitor of nitric oxide synthase) but not N-nitro-D-arginine methyl ester. Resting cardiovascular parameters did not change significantly following any of these manipulations. The results suggest that serotonin exerts an inhibitory modulation on the excitability of the midbrain defence area by a mechanism which involves nitric oxide.

Aphrodisiac property of Trichopus zeylanicus extract in male mice

Administration of Trichopus zeylanicus leaf (ethanol extract) to male mice stimulated their sexual behaviour as evidenced by an increase in number of mounts and mating performance. This activity of the ethanol extract was concentration dependent and destroyed by heat treatment at 100 degrees C for 15 min. Although oral administration of a single dose (200 mg/kg) was effective, daily administration of the extract for 6 days was found to be more effective. The pups fathered by the drug treated mice were found to be normal with reference to foetal growth, litter size and sex ratio. The water as well as n-hexane extracts of the plant leaf were inactive. The present study reveals for the first time the aphrodisiac activity of Trichopus zeylanicus, an endemic herb of India.

A proposed test battery and constellations of specific behavioral paradigms to investigate the behavioral phenotypes of transgenic and knockout mice

Behavioral phenotyping of transgenic and knockout mice requires rigorous, formal analyses. Well-characterized paradigms can be chosen from the established behavioral neuroscience literature. This review describes (1) a series of neurological and neuropsychological tests which are effectively used as a first screen for behavioral abnormalities in mutant mice, and (2) a series of specific behavioral paradigms, clustered by category. Included are multiple paradigms for each category, including learning and memory, feeding, analgesia, aggression, anxiety, depression, schizophrenia, and drug abuse models. Examples are given from the experiences of the authors, in applying these experimental designs to transgenic and knockout mice. Extensive references for each behavioral paradigm are provided, to allow new investigators to access the relevant literature on behavioral methodology.

Genetics of aggressive and violent behavior

This article develops the topic of the genetics of aggressive and violent behavior from three directions. Firstly, evidence from twin, family, and adoption studies will establish the case for the importance of genetically transmitted factors in the genesis of aggressivity from childhood through adulthood. Secondly, evidence from adoption studies will be presented to show that some environmental conditions interact with genetic factors in such a way as to suggest that the development of aggressivity requires that both genetic and environmental factors be present. Thirdly, additional and direct evidence of genetic factors in aggressivity is presented from the perspective of molecular genetics, where underlying biochemical mechanisms associated with aggressivity have been found to be caused by specific genes in animal models with confirmation of similar physiologic mechanisms in humans.

The neurobiology of impulsive aggression

As noted previously, it is likely that the tendency to lash out verbally or physically at others is influenced by an interaction among multiple complex biologic factors. We need to investigate how these systems interact with each other to develop a more thorough understanding of the brain's influence over aggressive behavior. We are at a very early stage in our understanding of the neurobiology of aggression. There are no simple tools for studying the complex neurophysiology of the human brain. The studies cited in this article include techniques limited in their utility. As our technologies improve, discovering a more thorough picture of the brain's influence over aggressive behavior may be possible. For example, functional neuroimaging may help to localize abnormal neurotransmitter functioning in the brains of individuals with impulsive aggressive behavior. Our technologies are beginning to reveal the differential effects of subsystems of neurotransmitter regulation. Subtypes of serotonin receptors may differentially mediate impulsive aggressive behaviors. Animal studies suggest that 5-HT 1A receptor stimulation results in a decrease in aggressive behavior. As noted previously, aggressive personality-disordered patients show a blunted prolactin response to the 5-HT1A agonist buspirone. Antagonism of 5-HT 2 receptors appears to decrease aggression, and this effect may explain the ability of newer antipsychotic agents (which, unlike older antipsychotic medications, block 5-HT 2 receptors) to produce a dramatic reduction in aggression and agitation independent of effects on psychotic symptoms. Neglecting psychosocial factors in the causes of aggressive behavior would also be naive. Although environmental factors account for much of the predisposition to aggression, there have been few systematic studies to explore the relationship between life experiences and aggression. In addition, there have been no well-designed studies of the interaction between biology and an individual's environment in the genesis of aggressive behavior. There is some evidence of an association between childhood abuse and neglect and adult antisocial personality disorder, but this relationship might be merely an artifact of the genetic relationship between parental and offspring antisocial personality disorder. As we discussed in the introduction, one of the biggest hurdles in the study of the neurobiology of aggression is the lack of a consensus on definitions. "Intermittent Explosive Disorder" is the only category in DSM-IV that directly addresses individuals with problems with aggression, but the criteria are vague and only focus on a handful of the many patients who exhibit problems with aggressive behavior. It is our hope that investigators in this field can work together toward developing more precise and encompassing diagnostic criteria to study effectively both the neurobiology and treatment of these disorders.

The use of genetic "knockout" mice in behavioral endocrinology research

The production of mice with specific deletion of targeted genes (knockouts) has provided a useful tool in understanding the mechanisms underlying behavior. There are many opportunities with this new tool for behavioral neuroendocrinology, specifically, and behavioral biology, generally. Although this genetic technique offers new opportunities to study the mechanisms of behavior, as with all behavioral techniques there are some potential limitations. For example, the products of many genes are essential to normal function, and inactivating the gene may prove lethal or induce gross morphological or physiological abnormalities that can complicate interpretation of discrete behavioral effects. Unexpected compensatory or redundancy mechanisms might be activated when a gene is missing and cloud interpretation of the normal contribution of the gene to behavior. Behavioral tests study the effects of the missing gene (and gene product), not the effects of the gene directly. This conceptual shortcoming can be overcome in the same way that it is overcome in other types of ablation studies, by collecting converging evidence using a variety of pharmacological, lesion, and genetic manipulations. Finally, because mammalian genome mapping is currently focused on mice (Mus musculus), standardized behavioral testing of mice should be adopted. Against those disadvantages are several important advantages to using knockout mice in behavioral research: (1) disabling a gene is often a very precise and "clean" ablation, (2) the effects of the gene product can be abolished without the side-effects of drugs, and (3) genetic manipulations may be the only way to determine the precise role of many endogenous factors on behavior. The use of new inducible knockouts, in which the timing and placement of the targeted gene disruption can be controlled, will be an extremely important tool in behavioral endocrinology research.

Serotonin and aggressive motivation in crustaceans: altering the decision to retreat

In crustaceans, as in most animal species, the amine serotonin has been suggested to serve important roles in aggression. Here we show that injection of serotonin into the hemolymph of subordinate, freely moving animals results in a renewed willingness of these animals to engage the dominants in further agonistic encounters. By multivariate statistical analysis, we demonstrate that this reversal results principally from a reduction in the likelihood of retreat and an increase in the duration of fighting. Serotonin infusion does not alter other aspects of fighting behavior, including which animal initiates an encounter, how quickly fighting escalates, or which animal eventually retreats. Preliminary studies suggest that serotonin uptake plays an important role in this behavioral reversal.

Mice selected for low and high blood magnesium levels: a new model for stress studies

Extra- and intracellular magnesium levels have previously been shown to be genetically controlled in humans and in the mouse. To further study this genetic regulation, mice were selected from a heterogeneous population, for low (MGL mice) and high (MGH mice) red blood cell (RBC) magnesium values. These values diverged rapidly in the two strains, to reach a stable difference between the 14th and 18th generations. MGL mice also exhibited significantly lower plasma, kidney, and skull bone magnesium contents and higher urinary magnesium excretion and total brain weights. Moreover, in stressful conditions, MGL mice displayed a more aggressive behavior that the control MGH strain. Altogether, MGL mice showed a more restless behavior, a higher rectal temperature, and much higher brain (+17%) and urine (+200%) noradrenaline levels than the MGH animals. These strains, thus, constitute a new animal model for the study of magnesium metabolism and its relationships with catecholamines, stress sensitivity, and aggressive behavior.

Absence of cerebellar long-term depression in mice lacking neuronal nitric oxide synthase

Extensive pharmacological evidence suggests that nitric oxide (NO) is a crucial transmitter for cerebellar long-term depression (LTD), a long-lasting decrease in efficacy of the synapses from parallel fibers onto Purkinje neurons, triggered by coincident presynaptic activity and postsynaptic depolarization. We now show that LTD cannot be induced in Purkinje neurons under whole-cell patch clamp in cerebellar slices from young adult mice genetically lacking neuronal nitric oxide synthase (nNOS). This genetic evidence confirms the essentiality of NO and nNOS for LTD in young adult rodents. Surprisingly, LTD in cells from nNOS knockout mice cannot be rescued by photolytic uncaging of NO and cGMP inside Purkinje neurons, although such stimuli circumvent acute pharmacological inhibition of nNOS and soluble guanylate cyclase in normal rodents. Also slices from knockout mice show no deficit in cGMP elevation in response to exogenous NO. Therefore, prolonged absence of nNOS allows atrophy of the signaling pathway downstream of cGMP.

Co-localization of androgen receptor and nitric oxide synthase in the ventral premammillary nucleus of the newborn rat: an immunohistochemical study

The distribution of the neuronal nitric oxide synthase (nNOS), androgen receptor (AR), estrogen receptor (ER) and aromatase (ARO) was studied in the dorsal and ventral premammillary nuclei (PMd and PMv) of the newborn rat by immunohistochemistry. In the intact male pups, nNOS immunoreactivity (-IR) was present both in the PMd and the PMv, while AR-IR was detected only in the PMv. On the other hand, ER-IR and ARO-IR were scarcely encountered in the both PMd and PMv. By double immunostaining of nNOS and AR, all the nNOS-IR cells in the PMv were revealed to contain AR-IR. In the intact female pups, nNOS-IR was present in the both PMd and PMv, but neither ER-, nor ARO-IR were detected in the PM region. In the PMv of the intact female rat, no AR-IR was detected at 6 days of age, while it was detected as only a faint staining within 12 h after birth. When the male pups were castrated neonatally, no AR-IR was detected in the PMv. Subcutaneous injections of 5alpha-dihydrotestosterone (DHT) induced strong AR-IR in the castrated male and the intact female pups. On the contrary, the intensity of nNOS-IR stayed unchanged among these animals. Neonatal androgen and nitric oxide has been considered important to brain development. Moreover, involvement of the PMv in aggressive and mating behavior of male animals has been reported. Together with the fact that the AR-IR and nNOS-IR were found in the same neurons in the PMv, involvement of this nucleus in masculinization of the brain by non-aromatizable androgen is postulated.

Behavioral symptoms in adult rats after postnatal L-nitro-arginine

We addressed experimentally the suggestion by Gally et al. [Gally J. A., Read Montague P., Reeke G. N. Jr and Edelman G. M. (1990) Proc. Natl Acad. Sci. U.S.A. 87, 3547-3551] that nitric oxide may play a role in the use-dependent modification of synaptic efficacy in the developing nervous system. In a preliminary control experiment, we treated rat pups from postnatal day 8 to postnatal day 22 with a nitric oxide synthase blocker (L-nitro-arginine) and compared their growth curves and brain weights to those of saline injected control pubs. No significant differences were found after the 14 days of nitric oxide synthase inhibition. In the subsequent experiment, we inhibited nitric oxide synthesis in rat pups from postnatal day 8 to day 29 and assessed their place learning ability and open field behavior as adults. We found an increased speed of habituation of locomotion in an open field in 5-month-old rats that had been treated postnatally with a nitric oxide synthase blocker. There was no difference between treated and non-treated rats with respect to place learning in a water maze. We conclude that perturbation of nitric oxide production during early postnatal development does not preclude normal learning and memory function in the adult.

Neuronal nitric oxide synthase alternatively spliced forms: prominent functional localizations in the brain

Neuronal nitric-oxide synthase (nNOS) is subject to alternative splicing. In mice with targeted deletions of exon 2 (nNOS(delta/delta)), two alternatively spliced forms, nNOS beta and gamma, which lack exon 2, have been described. We have compared localizations of native nNOS alpha and nNOS beta and gamma by in situ hybridization and immunohistochemistry in wild-type and nNOS(delta/delta) mice. To assess nNOS catalytic activity in intact animals we localized citrulline, which is formed stoichiometrically with NO, by immunohistochemistry. nNOS beta is prominent in several brain regions of wild-type animals and shows 2-to 3-fold up-regulation in the cortex and striatum of nNOS(delta/delta) animals. The persistence of much nNOS mRNA and protein, and distinct citrulline immunoreactivity (cit-IR) in the ventral cochlear nuclei and some cit-IR in the striatum and lateral tegmental nuclei, indicate that nNOS beta is a major functional form of the enzyme in these regions. Thus, nNOS beta, and possibly other uncharacterized splice forms, appear to be important physiological sources of NO in discrete brain regions and may account for the relatively modest level of impairment in nNOS(delta/delta) animals.

Acute inhibition of nitric oxide synthesis induces anxiolysis in the plus maze test

The involvement of nitric oxide (NO) in anxiety was investigated in rats, using the elevated plus maze test. Acute, but not chronic, systemic treatment with N omega-nitro-L-arginine methyl ester (L-NAME, 10 and 60 mg.kg-1), an inhibitor of NO synthase, increased the time spent by the rats in the open arms. Both the acute and chronic treatments with L-NAME inhibited NO synthase in endothelial cells and in the central nervous system, as shown by the increase in mean arterial pressure and decreased NO synthase activity in brain tissue. Chronic treatment with L-NAME also decreased the serum nitrate levels. The anxiolysis induced by acute L-NAME treatment is unlikely to be due to hypertension, since two-kidney one-clip hypertension in non-L-NAME-treated rats failed to significantly change exploratory behaviour in the elevated plus maze. These results indicate that acute inhibition of NO synthesis decreases anxiety in rats.

Sex differences in nitrite/nitrate levels and antioxidant defense in rat brain

This study assessed sex differences in stable metabolites of nitric oxide and major enzymes involved in antioxidant defense in various regions of rat brain. Nitrite/nitrate levels and activities of superoxide dismutase and catalase were determined in cortex, hippocampus, corpus striatum, midbrain and cerebellum of adult male and female Sprague-Dawley rats. Nitrite/nitrate levels were significantly higher in the cortex and the hippocampus of male than female rats, while catalase activity was higher in the cortex of females than in males. These sex differences may have significant effects on brain function in health and disease.