Functional magnetic resonance imaging in awake transgenic fragile X rats: evidence of dysregulation in reward processing in the mesolimbic/habenular neural circuit.

Anxiety and social deficits, often involving communication impairment, are fundamental clinical features of fragile X syndrome. There is growing evidence that dysregulation in reward processing is a contributing factor to the social deficits observed in many psychiatric disorders. Hence, we hypothesized that transgenic fragile X mental retardation 1 gene (fmr1) KO (FX) rats would display alterations in reward processing. To this end, awake control and FX rats were imaged for changes in blood oxygen level dependent (BOLD) signal intensity in response to the odor of almond, a stimulus to elicit the innate reward response. Subjects were 'odor naive' to this evolutionarily conserved stimulus. The resulting changes in brain activity were registered to a three-dimensional segmented, annotated rat atlas delineating 171 brain regions. Both wild-type (WT) and FX rats showed robust brain activation to a rewarding almond odor, though FX rats showed an altered temporal pattern and tended to have a higher number of voxels with negative BOLD signal change from baseline. This pattern of greater negative BOLD was especially apparent in the Papez circuit, critical to emotional processing and the mesolimbic/habenular reward circuit. WT rats showed greater positive BOLD response in the supramammillary area, whereas FX rats showed greater positive BOLD response in the dorsal lateral striatum, and greater negative BOLD response in the retrosplenial cortices, the core of the accumbens and the lateral preoptic area. When tested in a freely behaving odor-investigation paradigm, FX rats failed to show the preference for almond odor which typifies WT rats. However, FX rats showed investigation profiles similar to WT when presented with social odors. These data speak to an altered processing of this highly salient novel odor in the FX phenotype and lend further support to the notion that altered reward systems in the brain may contribute to fragile X syndrome symptomology.

Vasopressin-dependent flank marking in golden hamsters is suppressed by drugs used in the treatment of obsessive-compulsive disorder.

BACKGROUND: Alterations in arginine vasopressin regulation and secretion have been proposed as one possible biochemical abnormality in patients with obsessive-compulsive disorder. In golden hamsters, arginine vasopressin microinjections into the anterior hypothalamus trigger robust grooming and flank marking, a stereotyped scent marking behaviors. The intensity and repetition of the behaviors induced by arginine vasopressin is somewhat reminiscent of Obsessive Compulsive Disorder in humans. The present experiments were carried out to test whether pharmacological agents used to alleviate obsessive compulsive disorder could inhibit arginine vasopressin-induced flank marking and grooming. RESULTS: Male golden hamsters were treated daily for two weeks with either vehicle, fluoxetine, clomipramine, or desipramine (an ineffective drug), before being tested for arginine vasopressin-induced flank marking and grooming. Flank marking was significantly inhibited in animals treated with fluoxetine or clomipramine but unaffected by treatment with desipramine. Grooming behavior was not affected by any treatment. CONCLUSION: These data suggest that arginine vasopressin-induced flank marking may serve as an animal model for screening drugs used in the control of Obsessive Compulsive Disorder.

Neural connections of the anterior hypothalamus and agonistic behavior in golden hamsters.

In male golden hamsters, offensive aggression is regulated by an interaction between arginine-vasopressin and serotonin at the level of the anterior hypothalamus. The present studies were conducted to study a neural network underlying this interaction. The connections of the anterior hypothalamus were examined by retrograde and anterograde tracing in adult male hamsters. Several limbic areas were found to contain both types of tracing suggesting reciprocal connections with the anterior hypothalamus. Their functional significance relating to the consummation of aggression was tested by comparing neuronal activity (examined through quantification of c-Fos-immunolabeling) in two groups of animals. Experimental animals were sacrificed after attacking an intruder. Control animals were sacrificed after exposure to a woodblock carrying the odor of an intruder that elicited behaviors related to offensive aggression without its consummation. An increased density of Fos-immunoreactivity was found in experimental animals within the medial amygdaloid nucleus, ventrolateral hypothalamus, bed nucleus of the stria terminalis and dorsolateral part of the midbrain central gray. These data suggest that these areas are integrated in a neural network centered on the anterior hypothalamus and involved in the consummation of offensive aggression. Finally, c-Fos-immunoreactivity was combined with labeling of serotonin and vasopressin neurons to identify sub-populations particularly associated with offensive aggression. Vasopressin neurons in the nucleus circularis and medial division of the supraoptic nucleus showed increased neuronal activity in the fighters, supporting their role in the control of offensive aggression.

Adolescent stress and neural plasticity in hamsters: a vasopressin-serotonin model of inappropriate aggressive behaviour.

Animal studies show that arginine vasopressin facilitates aggression, while serotonin (5-HT) inhibits aggression by blocking the activity of the vasopressin system. Clinical studies report that subjects with a history of 'fighting and assault' show a significant positive correlation between cerebrospinal fluid concentrations of vasopressin and aggression in the presence of a hyporeactive 5-HT system. Thus, in animals and humans, a hyporeactive 5-HT system may result in enhanced vasopressin activity and increased aggression. Can the stress of emotional and physical insult, i.e. threat and attack, during adolescence affect the development of the vasopressin and 5-HT systems and alter normal aggressive behaviour in early adulthood? Adolescent male golden hamsters were weaned at postnatal day 25, and stressed for 2 weeks by daily 1 h bouts of threat and attack by adult hamsters. Male littermates were run in a parallel stress study using daily 1 h trials of isolation in a novel environment. During early adulthood, on postnatal day 45, 3 days after the cessation of stress trials, animals were tested for aggression in a resident: intruder model. The results show a context-dependent change in aggression. Animals with a history of abuse show exaggerated attack behaviour toward smaller males compared to littermates with a history of isolation stress. Conversely, when confronted by males of equal size, animals with a history of abuse show diminished aggression and increased submission compared to controls. It was determined that the density of vasopressin fibres and neurones in the hypothalamus is lower in abused animals compared to controls. In contrast, the number of 5-HT terminals within the hypothalamus is higher in abused animals compared to controls. These results provide evidence in an animal model that stress in the form of threat and attack during adolescence can alter the balance between vasopressin and 5-HT in the brain, resulting in inappropriate aggressive behaviour in early adulthood.

Absence of vasopressin expression by galanin neurons in the golden hamster: implications for species differences in extrahypothalamic vasopressin pathways.

In golden hamsters, there is a complete absence of the small diameter vasopressin (VP) neurons in the bed nucleus of the stria terminalis (BST) and medial amygdala (Me) which have been shown to exhibit steroid dependency and sexual dimorphism in many other rodent species. In rats, VP in the BST/Me is always colocalized with the neuropeptide galanin (GAL) and the sex difference in VP cell number appears to result from a sex difference in the number of GAL neurons which coexpress VP. Likewise, we reasoned that the species difference in extrahypothalamic VP pathways present in the golden hamster could result from a reduced coexpression of VP by GAL neurons in these regions. Here, we used in situ hybridization histochemistry to determine whether GAL mRNA expressing neurons are present in the BST and Me of golden hamsters despite the absence of VP expression in these regions. In addition, we have used slice binding and receptor autoradiography to identify specific GAL binding sites in the lateral septum, a probable target region of BST/Me neurons, and in situ hybridization to confirm that some of these binding sites correspond to the GALR1 GAL receptor subtype. Our findings indicate that the absence of VP expression in the BST/Me of golden hamsters results from a failure of extrahypothalamic GAL neurons to express the VP phenotype. Because GAL is expressed in the extended amygdaloid complex and GAL receptors are present in the septum of golden hamsters, GAL may play a role in modulating functions previously attributed to BST/Me pathways.

Testosterone facilitates aggression by modulating vasopressin receptors in the hypothalamus.

In many species, testosterone treatment facilitates offensive aggression tested in resident-intruder models. As the mechanisms of action of testosterone remain unclear, we hypothesized that testosterone interacts with neurotransmitter systems involved in the regulation of offensive aggression. We tested this hypothesis with the vasopressinergic system in golden hamsters in three separate experiments. First, we compared the density of V1 vasopressin (VAP) receptor binding between castrated animals treated with testosterone and their untreated controls. The most noticeable difference was found within the ventrolateral hypothalamus (VLH), a site involved in the control of aggression in several species of mammals. Within this area, V1 AVP receptor binding disappeared after castration, while being maintained by testosterone-treatment. Second, we tested behavioral effects of AVP within the VLH. Microinjections of AVP (100 nl, 1 or 100 microM) within the VLH accelerated the onset of offensive aggression in testosterone-treated animals. However, AVP-injected animals did not bite more than their vehicle-injected controls. Third, microinjections of AVP failed to activate offensive aggression in animals deprived of testosterone. As AVP receptors appeared to overlay previously described distributions of androgen and estrogen receptors in golden hamsters, we propose that testosterone facilitates the onset of offensive aggression, at least partly, through an activation of AVP receptors within the VLH.

Distribution of small vasopressinergic neurons in golden hamsters.

In rats, small (diameter: ca. 10 micrograms) vasopressinergic neurons have been localized in the forebrain, including extrahypothalamic sites, such as the bed nucleus of the stria terminalis (BST) and the medial amygdala (MeA). In golden hamsters, no such neurons have ever been described in extrahypothalamic sites, while their presence in some hypothalamic sites, such as the paraventricular nucleus (PVN), remains controversial. The present studies were carried out to confirm the existence of small vasopressinergic neurons in the forebrain of golden hamsters, using rats as a positive control. The presence of small vasopressinergic neurons in these sites was first tested by immunocytochemistry in colchicine-treated animals. The resulting distribution was corroborated by in situ hybridization for vasopressin (AVP) mRNA. While a large number of small AVP-immunoreactive (AVP-ir) neurons was found in the BST and MeA of colchicine-treated rats, none was found in the same locations in hamsters. Interestingly, as a few large (diameter: 20-25 micrograms) AVP-ir neurons were found in the BST just medial to the small neurons in rats, the same area contained a few large and small AVP-ir neurons in hamsters. In the PVN, large and small AVP-ir neurons were found in rats and hamsters. However, three to four times more neurons were counted in rats. These data were confirmed by in situ hybridization. Indeed, in hamsters, no labelling for AVP mRNA was detected in small neurons within the BST and MeA. Furthermore, the PVN of rats contained more labelling for AVP mRNA, as compared to hamsters. These results confirm that the distribution of vasopressinergic neurons in rats cannot be generalized to other species without a detailed analysis.

Sexual differences in the magnocellular vasopressinergic system in golden hamsters.

Golden hamsters, as compared to rats, lack several parvicellular vasopressinergic cell groups, particularly sexually dimorphic populations. We decided to test the possibility that magnocellular vasopressinergic neurons are subjected to sexual differences in hamsters, as they are known to display vasopressin (AVP)-dependent sexually dimorphic behaviors. The distribution of magnocellular vasopressinergic neurons was mapped and compared between males and females. Approximately 50% more vasopressin-immunoreactive (AVP-ir) neurons were counted in males within the medial and lateral divisions of the supraoptic nucleus. Furthermore, levels of AVP extracted from the hypothalamus and the pituitary gland were three to four times higher in males than in females. Finally, hypothalamic extracts from a male and a female hypothalamus were fractionated by HPLC and assayed for AVP immunoreactivity. Immunoreactivity from each extract had the same retention time as synthetic AVP standards; and the levels were twice as high in the male. These results support the existence of sexual differences in the magnocellular vasopressinergic system in golden hamsters. These differences appear to be related to previously reported sexual differences in AVP secretion from the neurohypophysis.

Evidence for a functional and anatomical relationship between the lateral septum and the hypothalamus in the control of flank marking behavior in Golden hamsters.

Golden hamsters with established dominant/subordinate relationships communicate their social status by rubbing pheromone-producing flank glands against objects in the environment. This behavior, called flank marking, is controlled by vasopressin-sensitive neurons localized to the anterior hypothalamus. Vasopressinergic magnocellular neurons in the nucleus circularis and medial aspect of the supraoptic nucleus are thought to be a source of neurotransmitter for the initiation of flank marking. The present study was undertaken to examine the extrahypothalamic control of flank marking. The anatomical and functional connections between the lateral septum and the vasopressin-containing nuclear groups in and around the anterior hypothalamus were examined by: (1) tracing afferent and efferent connections following microinjection of horseradish peroxidase and Phaseolus vulgaris-leucoagglutinin into the lateral septum, and (2) recording odor-induced flank marking prior to and following ibotenate lesions in the septum. The greatest number of perikarya retrogradely labeled with horseradish peroxidase were found lateral to the anterior hypothalamus and ventral to the fornix in the area of the lateral hypothalamus. The vasopressin-containing nuclear groups, e.g., paraventricular, supraoptic, suprachiasmatic nuclei, and the nucleus circularis, were devoid of labeled perikarya. Nerve terminals anterogradely labeled with Phaseolus vulgaris-leucoagglutinin were primarily localized to the anterior hypothalamus, in and around the nucleus circularis, and the medial aspect of the supraoptic nucleus. The lateral aspect of the supraoptic nucleus was devoid of nerve terminals as were the paraventricular and suprachiasmatic nuclei. The anatomical connections between the lateral septum and the hypothalamus appear to be necessary for the control of flank marking, since the microinjection of ibotenate into this limbic site significantly reduced odor-induced flank marking as compared to control microinjections of 0.9% NaCl.

A V1-like receptor mediates vasopressin-induced flank marking behavior in hamster hypothalamus.

A vasopressin-sensitive mechanism within the medial preoptic area-anterior hypothalamus (MPOA-AH) appears to be essential for expression of a complex behavior involved in olfactory communication in Golden hamsters called flank marking. The present study investigated whether the induction of flank marking by arginine-vasopressin (AVP) within the MPOA-AH is mediated by a receptor that is more similar to the vasopressor (V1) or the antidiurectic (V2) AVP receptor. Adult male hamsters were anesthetized and implanted with a 26 gauge guide cannula stereotaxically aimed at the MPOA-AH and then microinjected with analogs of vasopressin, oxytocin, and selective V1 and V2 antagonists. Hamsters were tested for flank-marking behavior during a 5 or 10 min observation period following the injection of peptide in a vehicle of 100 nl of saline. None of the 15 analogs of AVP and oxytocin produced more flank marking than the 50.8 +/- 16.2 and 76.8 +/- 4.4 (mean +/- SEM; n = 4) flank marks observed following injection of AVP at the 1 or 10 ng dose, respectively. The number of flank marks produced by each analog was found to be highly related to the pressor activity of that analog at both the 1 ng (rho = +0.74, p less than 0.01) and 10 ng (rho = +0.82, p less than 0.01) doses. In contrast, no statistically reliable relationship between flank marking and the antidiuretic activity of these analogs was found at either dose (1 ng: rho = +0.07, p greater than 0.05; 10 ng: rho = +0.10, p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Microinjection of kainic acid into the hypothalamus of golden hamsters prevents vasopressin-dependent flank-marking behavior.

The purpose of this study was to define the vasopressin-sensitive area in the anterior hypothalamus-medial preoptic area (AH-MPOA) of the golden hamster that is involved in the expression of flank-marking behavior. Male hamsters implanted with guide cannulae stereotaxically aimed at various sites in the AH-MPOA were microinjected initially with 0.1 ng of arginine vasopressin (AVP) in a volume of 10 nl. Hamsters that flank-marked in response to these injections were subsequently microinjected into the same sites with kainic acid (0.2 microgram/20 nl; n = 10) or an equal volume of 1 M NaOH as a vehicle control (n = 10). Four days later hamsters were tested for odor-induced flank marking by placing them into the recently vacated home cage of other hamsters and for flank marking in response to the microinjection of AVP. Animals treated with kainic acid exhibited significantly (p less than 0.01) fewer AVP and odor-induced flank marks as compared to the number of flank marks observed prior to treatment. There was no significant reduction in the number of flank marks in hamsters microinjected with the NaOH vehicle. In another group of hamsters, microinjection of kainic acid (0.2 microgram/20 nl) into the 3rd ventricle (n = 4) and other sites of the hypothalamus (n = 4) did not significantly alter odor-induced flank marking. The locations of the microinjection sites indicate that the neurons sensitive to AVP and involved in the expression of flank-marking behavior are found in the ventromedial area of the AH-MPOA extending from the caudal border of the suprachiasmatic nucleus to the rostral limit of the supraoptic nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasopressin injected into the hypothalamus triggers a stereotypic behavior in golden hamsters.

Microinjection of arginine vasopressin into the medial preoptic area of the hypothalamus of male and female golden hamsters triggered a complex, stereotypic behavior--flank marking--a type of scent marking used in olfactory communication. The flank marking was not elicited by saline, oxytocin, neurotensin, or angiotensin II. Vasopressin was ineffective when injected into other areas of the hypothalamus or into the lateral cerebroventricle.

A functional analysis of dopaminergic innervation of the neurohypophysis.

Dopaminergic neurons arising from cell bodies in the rostral arcuate nucleus of the hypothalamus have been shown to make axoaxonic contact with neurohypophyseal neurosecretory axons. In this study, electrical stimulation of the rostral arcuate nucleus depresses multiunit electrical activity recorded from neurosecretory axons within the neurohypophysis. After a single 5-s stimulus train, neurohypophyseal electrical activity is reduced to 6% of control. The superfusion of dopamine (5 micrograms/microliters) onto the neurohypophysis also has an inhibitory effect. Superfusion directly onto the neurohypophysis of the dopamine-receptor antagonist, pimozide (1 micrograms/microliters), abolishes the inhibitory effect of arcuate nucleus stimulation. These findings suggest that the dopaminergic innervation of the neurohypophysis may have an inhibitory influence on the release of neurohypophyseal hormones.