Ingestive behaviors of the rat deficient in vasopressin synthesis (Brattleboro strain). Effect of chronic treatment by dDAVP

Reducing sugar intake through chronic swimming training: Exploring palatability changes and central vasopressin mechanisms

Excessive sugar intake has been associated with the onset of several non-communicable chronic diseases seen in humans. Physical activity could affect sweet taste perception which may affect sugar intake. Therefore, it was investigated the chronic effects of swimming training on sucrose intake/preference, reactivity to sucrose taste, self-care in neurobehavioral stress, and the possible involvement of the vasopressin type V1 receptor in sucrose solution intake. Male Wistar rats, of from different cohorts were used, subjected to a sedentary lifestyle (SED) or swimming training (TR - 1 h/day, 5×/week, for 8 weeks, with no added load). Weekly intake was verified in SED and TR rats after access to a sucrose solution 1×/week, 2 h/day, for eight weeks. Chronic effects of swimming and/or a sedentary lifestyle were carried out three days after the end of the physical exercise protocol. Swimming training reduced the intake of sucrose solution from the third week onwards in the two-bottle test measured once a week for 8 weeks. After the ending of the swimming protocol, sucrose intake was also reduced as per its preference. This reduced intake is probably correlated with the carbohydrate aspect of sucrose since saccharin intake was not affected. In addition, chronic swimming training was shown to reduce ingestive responses, increase neutral responses, without interfering with aversive, in the sucrose solution taste reactivity test. In addition, these results are not related to a depressive-like behavior, nor to neurobehavioral stress. Furthermore, treatment with vasopressin V1 receptor antagonist abolished the reduced sucrose intake in trained rats. The results suggest that swimming performed chronically is capable of reducing intake and preference for sucrose by decreasing the palatability of sucrose without causing depressive-type behavior or stress. In addition, the results also suggest that central V1 vasopressin receptors are part of the mechanisms activated to reduce sucrose intake in trained rats.

The role of glucagon-like peptide-1 (GLP-1) in fluid and food intakes in vasopressin-deficient Brattleboro rats

Eating and drinking co-occur and many of the same mechanisms that control one are involved in the control of the other, making it difficult to isolate specific mechanisms for the control of fluid intake. Glucagon-like peptide-1 (GLP-1) is a peptide that seems to be involved in the endogenous control of both ingestive behaviors, but we lack a thorough understanding of how and where GLP-1 is acting to control fluid intake. Vasopressin-deficient Brattleboro rats are a model of hereditary hypothalamic diabetes insipidus that have been used extensively for the study of vasopressin actions in behavior and physiology. Here, we propose that these rats, that eat normally but drink excessively, provide a useful model to dissociate central controls of food and fluid intakes. As an initial step toward establishing this model for these purposes, we focused on GLP-1. Similar to the effect observed after treatment with a GLP-1 receptor (GLP-1R) agonist, the intake difference between wildtype and Brattleboro rats was largely a function in the number of licking bursts, indicating differences in post-ingestive feedback (e.g., satiation). When given central injections of a GLP-1R agonist, the effect on feeding was comparable between wildtype and Brattleboro rats, but the effect of drug on fluid intake was markedly exaggerated in Brattleboro rats. Additionally, Brattleboro rats did not respond to GLP-1R antagonism, whereas wildtype rats did. Taken together, these results suggest that Brattleboro rats exhibit a selective disruption to GLP-1's control of water intake. Overall, these experiments provide foundational studies of the ingestive behavior of Brattleboro rats and demonstrate the potential to use these rats to disentangle the effects of GLP-1 on food and fluid intakes.

Exogenous central angiotensin fails to stimulate a sodium appetite in diabetes insipidus Brattleboro rats

We investigated the effect of central administration of angiotensin II (AngII) on a specific salt appetite (SSA) in homozygous diabetes insipidus Brattleboro (DI) rats because this stimulus induces such a response in all other rat strains. DI rats have a deficiency in the synthesis of arginine vasopressin (AVP) and a reduced content of pituitary oxytocin (OT). They are characterized also by polyuria, polydipsia, and they seldom ingest high concentrations of NaCl solutions. We also tested if the appetite can be influenced by neurohypophyseal hormones especially oxytocin (OT) because it inhibits SSA in other animals. DI rats and Long Evans (LE) controls were fed ad libitum and given a choice between water, and either 0.9% or 1.8% NaCl. The data showed a significant increase of daily spontaneous water intake in DI compared with LE rats. Both DI and LE ingested similar small spontaneous volumes of the isotonic NaCl solution, but DI rats drank significantly less hypertonic NaCl than the LE controls. I.c.v infusion of AngII induced significant sodium intake in LE rats, but only raised water intake in DI rats. When combined with i.c.v. Ang II, OVT enhanced salt intake in LE animals while AVP attenuated water intake in both groups of rats and blocked NaCl intake completely in LE rats. In conclusion, DI rats did not demonstrate a SSA in response to central administration of AngII, although the drinking of water was enhanced. In combination with i.c.v. AngII, AVP inhibits water drinking in both DI and LE rats. In the LE controls OT attenuates AngII-induced SSA but has no effect in DI rats.

Cellular and subcellular evidence for neuronal interaction between the chemokine stromal cell-derived factor-1/CXCL 12 and vasopressin: regulation in the hypothalamo-neurohypophysial system of the Brattleboro rats

We previously described a colocalization between arginine vasopressin (AVP) and the chemokine stromal cell-derived factor-1alpha (SDF-1) in the magnocellular neurons of both the hypothalamic supraoptic and paraventricular nucleus as well as the posterior pituitary. SDF-1 physiologically affects the electrophysiological properties of AVP neurons and consequently AVP release. In the present study, we confirm by confocal and electron microscopy that AVP and SDF-1 have a similar cellular distribution inside the neuronal cell and can be found in dense core vesicles in the nerve terminals in the posterior pituitary. Because the Brattleboro rats represent a good model of AVP deficiency, we tested in these animals the fate of SDF-1 and its receptor CXCR4. We identified by immunohistochemistry that both SDF-1 and CXCR4 immunoreactivity were strongly decreased in Brattleboro rats and were strictly correlated with the expression of AVP protein in supraoptic nucleus, paraventricular nucleus, and the posterior pituitary. We observed by real-time PCR an increase in SDF-1 mRNA in both heterozygous and homozygous rats. The effect on the SDF-1/CXCR4 system was not linked to peripheral modifications of kidney water balance because it could not be restored by chronic infusion of deamino-8D-ariginine-vasopressin, an AVP V2-receptor agonist. These original data further suggest that SDF-1 may play an essential role in the regulation of water balance.

The effects of chronic administration of established and putative antipsychotics on natural prepulse inhibition deficits in Brattleboro rats

We previously reported that vasopressin deficient Brattleboro (BRAT) rats exhibit deficits in prepulse inhibition (PPI) of the startle reflex that are consistent with PPI deficits exhibited by patients with schizophrenia and other neuropsychiatric disorders. Preliminary evidence indicates that this may be the basis of a predictive model for antipsychotic drug efficacy. Here we report the effects of acute and chronic administration of established and putative antipsychotics on these PPI deficits. BRAT rats, compared to their derivative strain, Long Evans rats, exhibited significantly decreased PPI and startle habituation consistent with patients with schizophrenia and other neuropsychiatric disorders. The second generation antipsychotics, risperidone and clozapine as well as a neurotensin agonist (PD149163) increased BRAT rat PPI, whereas saline, the typical antipsychotic, haloperidol, and a vasopressin analog (1-desamino-D-arginine vasopressin) did not. Similar to their effects in humans, chronic administration of antipsychotic drugs produced stronger effects than acute administration. These results further support the BRAT rat as a model of sensorimotor gating deficits with predictive validity for antipsychotics. The model appears to be able to differentiate first generation from second generation antipsychotics, identify putative antipsychotics with novel mechanisms (i.e., peptides) and reasonably model the therapeutic time course of antipsychotic drugs in humans.

Galanin receptor antagonists decrease fat preference in Brattleboro rat

The Brattleboro rat eats spontaneously 46% of its diet per day in fat when given a choice of carbohydrate, protein and fat. An overexpression of galanin (GAL) has been also observed in the hypothalamic paraventricular nuclei (PVN). This associative correlation has led to a hypothesis of a functional relation between central galanin expression and the preference for a lipid diet. In the present experiments, the effects of two GAL receptor antagonists, C7 and galantide, on fat consumption and central overexpression of GAL were investigated. Both antagonists were injected into either the cerebral ventricles or directly above the PVN, and the diet consumption followed for the subsequent 24h. C7 decreased significantly fat consumption when injected into the ventricles or directly above the PVN. In contrast, galantide must be injected above the PVN to show the same effect. However, the two antagonists did not modify GAL mRNA expression in the PVN when they were injected 2h before sacrifice. These experiments confirm a functional link between the preferential consumption of fat and hypothalamic Galanin; different subtypes of the GAL receptor are probably involved, since both Galanin antagonists were differently efficient in decreasing spontaneous fat selection of the Brattleboro rat.

Vasopressin-deficient rats exhibit sensorimotor gating deficits that are reversed by subchronic haloperidol

BACKGROUND

Brattleboro (BB) rats are Long Evans rats with a single base pair genetic mutation that impairs their ability to synthesize vasopressin, a neurotransmitter and neurohormone. Brattleboro rats are known to have deficits in memory, emotional reactivity, motivation, attention, and social recognition, abnormalities associated with schizophrenia. Prepulse inhibition (PPI) of the acoustic startle reflex (ASR) is a measure of sensorimotor gating. Prepulse inhibition is deficient in unmedicated schizophrenia patients, and PPI deficits in schizophrenia may be related to the cognitive and behavioral abnormalities associated with this disorder. In this study we tested the hypothesis that BB rats exhibit PPI deficits analogous to those exhibited by schizophrenia patients.

METHODS

In one experiment, BB rats homozygous (BB-Ho) or heterozygous (BB-Hz) for the mutated vasopressin gene were compared with normal Long Evans (LE) rats from the same breeder source. In separate studies, BB-Ho and LE rats were treated with acute or subchronic (22 days) injections of haloperidol.

RESULTS

Both BB-Ho and BB-Hz rats had significantly higher ASR and significantly lower PPI compared with LE rats, with BB-Ho rats exhibiting the lowest PPI among all three genotypes. Furthermore, a single subcutaneous (SC) injection of haloperidol (0.5 mg/kg) did not reverse the PPI deficits in BB rats. In contrast, daily SC administration of haloperidol for 22 days reversed PPI deficits in BB rats.

CONCLUSIONS

These results suggest that PPI deficient BB rats may be an important genetic model of PPI deficits, which may help elucidate genetic, pharmacologic, and pathophysiologic mechanisms underlying PPI deficits and the effects of antipsychotic drugs on PPI.

CSF oxytocin and vasopressin levels after recovery from bulimia nervosa and anorexia nervosa, bulimic subtype

BACKGROUND

When ill, people with eating disorders have disturbances of the neuropeptides vasopressin and oxytocin.

METHODS

To avoid the confounding effects of the ill state, we studied women who were recovered (more than 1 year, normal weight, and regular menstrual cycles, no bingeing or purging) from bulimia nervosa (rBN) or binge eating/purging-type anorexia nervosa (rAN-BN), and matched healthy control women.

RESULTS

Vasopressin was elevated in rAN-BN and showed a trend towards elevation in rBN. In rBN, elevated cerebrospinal fluid vasopressin may be related to having a lifetime history of major depression. In comparison, cerebrospinal fluid oxytocin was normal in recovered subjects, but elevated levels in some rBN might be related to birth control pill use.

CONCLUSIONS

These data confirm and extend the possibility that elevated cerebrospinal fluid vasopressin may be related to the pathophysiology of eating disorders, and/or a lifetime history of major depression.

Dietary preferences of Brattleboro rats correlated with an overexpression of galanin in the hypothalamus

Galanin (GAL) is a neuropeptide cosynthesized with vasopressin (AVP) in neurons of the hypothalamo-neurohypophysial system. It increases food intake when injected into the brain and elicits an overconsumption of fat. The Brattleboro rat (DI) is genetically unable to produce AVP; the AVP-deficient-producing neurons of the hypothalamo-neurohypophysial system of DI rats are chronically stimulated and DI rats suffer from diabetes insipidus. We studied the central expression of GAL and the dietary preferences in the DI rat. GAL was overexpressed in the hypothalamus of the DI rat. GAL mRNA was higher by 1.8-fold in the supraoptic (P < 0.05) and by four-fold in the paraventricular nuclei (P < 0.001) of male and female DI rats compared with those of control Long Evans (LE) rats. However, GAL mRNA was lower in the arcuate nuclei of DI rats and equal to that of LE rats in the dorsomedian nuclei. We also measured a high preference for a lipid diet (45% of the daily consumption) when DI rats ate from a choice of the three macronutrients. Chronic infusion with deamino-8D-AVP (agonist of AVP V2 receptors) prevented the diabetes insipidus and the chronic stimulation of the hypothalamo-neurohypophysial system of the DI rats. However, the treatment did not suppress the overexpression of GAL, nor did it affect the rats' preference for a lipid diet. We conclude that the DI rat provides a novel animal model in which a spontaneous dietary preference correlates with the overexpression of one of the hypothalamic peptides, GAL.