The Neonatal Treatment of Rats with Monosodium Glutamate Induces Morphological Changes in the Subfornical Organ

Neonatal monosodium glutamate treatment counteracts circadian arrhythmicity induced by phase shifts of the light-dark cycle in female and male Siberian hamsters

Studies of rats and voles suggest that distinct pathways emanating from the anterior hypothalamic-retrochiasmatic area and the mediobasal hypothalamic arcuate nucleus independently generate ultradian rhythms (URs) in hormone secretion and behavior. We evaluated the hypothesis that destruction of arcuate nucleus (ARC) neurons, in concert with dampening of suprachiasmatic nucleus (SCN) circadian rhythmicity, would compromize the generation of ultradian rhythms (URs) of locomotor activity. Siberian hamsters retain-->of both sexes treated neonatally with monosodium glutamate (MSG) that destroys ARC neurons were subjected in adulthood to a circadian disrupting phase-shift protocol (DPS) that produces SCN arrhythmia. MSG treatments induced hypogonadism and obesity, retain-->and markedly reduced the size of the optic chiasm and optic nerves. MSG-treated hamsters exhibited normal entrainment to the light-dark cycle, but MSG treatretain-->ment counteracted the circadian arrhythmicity induced by the DPS protocol: only 6% of retain-->MSG-treated hamsters exhibited circadian arrhythmia, whereas 50% of control hamsters were circadian disrupted. In MSG-treated hamsters that retained circadian rhythmicity after DPS treatment, quantitative parameters of URs appeared normal, but in the two MSG-treated hamsters that became circadian arrhythmic after DPS, both dark-phase and light-phase URs were abolished. Although preliminary, these data are consistent with reports in voles suggesting that the combined disruption of SCN and ARC function impairs the expression of behavioral URs. The data also suggest that light thresholds for entrainment of circadian rhythms may be lower than those required to disrupt circadian organization.

Sex-dimorphism in cardiac nutrigenomics: effect of trans fat and/or monosodium glutamate consumption

BACKGROUND

A paucity of information on biological sex-specific differences in cardiac gene expression in response to diet has prompted this present nutrigenomics investigation. Sexual dimorphism exists in the physiological and transcriptional response to diet, particularly in response to high-fat feeding. Consumption of Trans-fatty acids (TFA) has been linked to substantially increased risk of heart disease, in which sexual dimorphism is apparent, with males suffering a higher disease rate. Impairment of the cardiovascular system has been noted in animals exposed to Monosodium Glutamate (MSG) during the neonatal period, and sexual dimorphism in the growth axis of MSG-treated animals has previously been noted. Processed foods may contain both TFA and MSG.

METHODS

We examined physiological differences and changes in gene expression in response to TFA and/or MSG consumption compared to a control diet, in male and female C57BL/6J mice.

RESULTS

Heart and % body weight increases were greater in TFA-fed mice, who also exhibited dyslipidemia (P < 0.05). Hearts from MSG-fed females weighed less than males (P < 0.05). 2-factor ANOVA indicated that the TFA diet induced over twice as many cardiac differentially expressed genes (DEGs) in males compared to females (P < 0.001); and 4 times as many male DEGs were downregulated including Gata4, Mef2d and Srebf2. Enrichment of functional Gene Ontology (GO) categories were related to transcription, phosphorylation and anatomic structure (P < 0.01). A number of genes were upregulated in males and downregulated in females, including pro-apoptotic histone deacetylase-2 (HDAC2). Sexual dimorphism was also observed in cardiac transcription from MSG-fed animals, with both sexes upregulating approximately 100 DEGs exhibiting sex-specific differences in GO categories. A comparison of cardiac gene expression between all diet combinations together identified a subset of 111 DEGs significant only in males, 64 DEGs significant in females only, and 74 transcripts identified as differentially expressed in response to dietary manipulation in both sexes.

CONCLUSION

Our model identified major changes in the cardiac transcriptional profile of TFA and/or MSG-fed mice compared to controls, which was reflected by significant differences in the physiological profile within the 4 diet groups. Identification of sexual dimorphism in cardiac transcription may provide the basis for sex-specific medicine in the future.

Nitric oxide and L-type calcium channel influences the changes in arterial blood pressure and heart rate induced by central angiotesin II

We study the voltage dependent calcium channels and nitric oxide involvement in angiotensin II-induced pressor effect. The antipressor action of L-Type calcium channel antagonist, nifedipine, has been studied when it was injected into the third ventricle prior to angiotensin II. The influence of nitric oxide on nifedipine antipressor action has also been studied by utilizing NW-nitro-L-arginine methyl ester (LNAME) (40 mug/0.2 mul) a nitric oxide synthase inhibitor and L-arginine (20 mug/0.2 mul), a nitric oxide donor agent. Adult male Holtzman rats weighting 200-250 g, with cannulae implanted into the third ventricle were injected with angiotensin II. Angiotensin II produced an elevation in mean arterial pressure and a decreased in heart rate. Such effects were potentiated by the prior injection of LNAME. L-arginine and nifedipine blocked the effects of angiotensin II. These data showed the involvement of L-Type calcium channel and a free radical gas nitric oxide in the central control of angiotensin II-induced pressor effect. This suggested that L-Type calcium channel of the circunventricular structures of central nervous system participated in both short and long term neuronal actions of ANG II with the influence of nitrergic system.

Changes in open-field activity and novelty-seeking behavior in periadolescent rats neonatally treated with monosodium glutamate

Monosodium glutamate (MSG) treatment of neonatal rodents leads to degeneration of the neurons in the arcuate nucleus, inner retinal layers and various other brain areas. It also causes various changes in the motor activity, sensory performance and learning abilities. We have previously shown that MSG treatment delays the appearance of some reflexes during neurobehavioral development and leads to temporary changes in reflex performance and motor coordination. Investigation of novelty-seeking behavior is of growing importance for its relationship with sensitivity to psychomotor stimulants. Perinatal administration of numerous toxic agents has been shown to influence novelty-seeking behavior in rats, but little is known about the influence of neonatal MSG treatment on the novelty-seeking behavior. The aim of the present study was to compare changes in locomotor, spontaneous exploratory and novelty-seeking behavior in periadolescent rats neonatally treated with MSG. Newborn rats were treated with 4 mg/g MSG subcutaneously on postnatal days 1, 3, 5, 7 and 9. Open-field behavior was tested at 2, 3, 4, 6 and 8 weeks of age. We found that MSG administration led to only temporary increases in locomotor behavior, which was more pronounced during the first few postnatal weeks, followed by a subtle hypoactivity at 2 months of age. Novelty-seeking was tested in four 5-min trials at 3 weeks of age. Trial 1 was in an empty open-field, two identical objects were placed in the arena during trial 2 and 3, and one of them was replaced to a novel object during trial 4. We found that the behavioral pattern of MSG-treated rats was the opposite in all tested signs in the novelty exploration test compared to control pups. In summary, our present study shows that neonatal MSG treatment leads to early temporary changes in the locomotor activity followed by hypoactivity at 2 months of age. Furthermore, MSG-treated rats show a markedly disturbed novelty-seeking behavior represented by altered activity when subjected to a novel object.

Functional relationship between subfornical organ cholinergic stimulation and nitrergic activation influencing cardiovascular and body fluid homeostasis

We have studied the effects of L-NG-nitro arginine methyl esther (L-NAME), L-arginine (LAR), inhibitor and a donating nitric oxide agent on the alterations of salivary flow, water intake, arterial blood pressure (MAP) and heart rate (HR) induced by the injection pilocarpine into the subfornical organ (SFO). Rats (Holtzman 250-300 g) were anesthetized with 2, 2, 2-tribromoethanol (20 mg/100 kg b. wt.) and a stainless steel cannula were implanted into their SFO. The volume of injection was 0.2 microl. The amount of saliva secretion was studied over a 5-min period. Pilocarpine (40 microg), L-NAME (40 microg) and LAR (30 microg) were used in all experiments for the injection into the SFO. Pilocarpine (10, 20, 40, 80 and 160 microg) injected into SFO elicited a concentration-dependent increase in salivary secretion. L-NAME injected prior to pilocarpine into the SFO increased salivary secretion and water intake due to the effect of pilocarpine. LAR injected prior to pilocarpine into the SFO attenuated the salivary secretion and water intake. Pilocarpine, injected into the SFO increased the MAP and decreased heart rate (HR). L-NAME injected prior to pilocarpine into the SFO potentiated the pressor effect of pilocarpine with a decrease in HR. LAR injected into the SFO prior to pilocarpine attenuated the increase in MAP with no changes in HR. The present study suggests that the SFO nitrergic cells interfere in the cholinergic pathways implicated in the control of salivary secretion, fluid and cardiovascular homeostasis.

Central but not peripheral glucoprivation is impaired in monosodium glutamate-treated rats

In the present study, newborn male Wistar rats were injected, subcutaneously, five times, every other day, with monosodium glutamate (MSG, 4 g/kg bw) or saline (as control, C), during the neonatal period. MSG animals developed destruction of the arcuate nuclei (ARC) with absence of NPY-immunoreactive cell bodies, which impaired both the food intake (baseline) and the 2-deoxy-D-glucose (2DG) glucoprivic feeding response. Increases in the immunoreactivity of corticotropin-releasing hormone-cell bodies in the paraventricular nuclei might have developed to compensate for the atrophy of the pituitary in MSG-treated rats. After systemic 2DG injection, neither the C nor the MSG rats increased their food intake, but they showed similar hyperglycemic responses, whereas plasma free fatty acids (FFA) increased only in the C group. In other groups, 2DG, norepinephrine (NE), neostigmine (NEO) and saline were intracerebroventricularly (i.c.v.) administered. In this condition, impairment of the hyperglycemic and food intake responses, associated to a lower increase in plasma FFA levels, were observed. As opposed to this, the MSG treatment gives support to NE effects, enhancing food intake, as well as plasma glucose and FFA levels. After NEO, plasma glucose increased only in the MSG group, while plasma FFA levels were elevated in the C rats. Taken together, the results obtained after MSG treatment point to a separate neural control of the hyperglycemic response and of the lipid mobilization when stimulated by central 2DG, NE or NEO administration. It seems likely that the excitatory neural pathway that controls lipid metabolism and is present in C rats was destroyed by the MSG treatment.

Development of neurological reflexes and motor coordination in rats neonatally treated with monosodium glutamate

Monosodium glutamate (MSG) treatment of neonatal rats causes neuronal degeneration in various brain areas and leads to several neurochemical, endocrinological and behavioral alterations. However, relatively little is known about the development of neurological reflexes and motor coordination of these animals. Therefore, the aim of the present study was to examine the neurobehavioral development of newborn rats treated with MSG. Rats received MSG at postnatal days 1, 3, 5, 7, and 9. Appearance of neural reflexes and reflex performance as well as motor coordination were examined for 5 weeks after birth. The efficacy of MSG treatment was confirmed by histological examination of the arcuate nucleus. We found that MSG treatment delayed the appearance of forelimb placing, forelimb grasp and righting reflexes, besides the retarded somatic development. The treated pups performed surface righting in significantly longer times. Also, worse performance was observed in the foot-fault and rota-rod tests. However, MSG-treated rats reached control levels by the end of the fifth postnatal week. These results show that MSG treatment does not cause permanent alterations in the neurobehavioral development, only delays the appearance of some reflexes and leads to temporary changes in reflex performance and motor coordination signs.