ABSTRACT
OBJECTIVE: The nucleus accumbens (NAc) plays critical roles in eating and food seeking in rodents and humans. Diets high in fats and sugars ("junk food") produce persistent increases in NAc function in male obesity-prone rats. This study examines effects of junk food and junk food deprivation on NAc core medium spiny neuron (MSN) excitability and glutamate transmission in females. METHODS: Obesity-prone female rats were given access to ad libitum junk food for 10 days, and recordings were made from MSNs in the NAc core immediately or after a short (27-72 hours) or long (14-16 days) junk food deprivation period in which rats were returned to ad libitum standard chow. Controls remained on chow throughout. Whole-cell slice electrophysiology was used to examine MSN intrinsic membrane and firing properties and glutamatergic transmission. RESULTS: The study found that intrinsic excitability was reduced, whereas glutamatergic transmission was enhanced, after the short, but not long, junk food deprivation period. A brief junk food deprivation period was necessary for increases in NAc calcium-permeable-AMPA receptor transmission and spontaneous excitatory postsynaptic current (sEPSC) frequency, but not for increases in sEPSC amplitude. CONCLUSIONS: This study reveals that females are protected from long-lasting effects of sugary fatty foods on MSN neuronal function and provides evidence for sex-specific effects on plasticity in brain centers that influence food-seeking and feeding behavior.
Subject(s)
Nucleus Accumbens , Obesity , Humans , Rats , Male , Female , Animals , Diet , Feeding Behavior , FoodABSTRACT
The dopaminergic and histaminergic systems are the first to appear during the development of the nervous system. Through the activation of H1 receptors (H1Rs), histamine increases neurogenesis of the cortical deep layers, while reducing the dopaminergic phenotype (cells immunoreactive to tyrosine hydroxylase, TH+) in embryo ventral mesencephalon. Although the function of histamine in neuronal differentiation has been studied, the role of H1Rs in neurogenesis has not been addressed. For this purpose, the H1R antagonist/inverse agonist chlorpheniramine was systemically administered (5 mg/kg, i.p.) to pregnant Wistar rats (gestational days 12-14, E12-14), and control and experimental embryos (E14 and E16) and pups (21-day-old) were evaluated for changes in nigro-striatal development. Western blot and immunohistochemistry determinations showed a significant increase in the dopaminergic markers' TH and PITX3 in embryos from chlorpheniramine-treated rats at E16. Unexpectedly, 21-day-old pups from the chlorpheniramine-treated group, showed a significant reduction in TH immunoreactivity in the substantia nigra pars compacta and dorsal striatum. Furthermore, striatal dopamine content, evoked [3H]-dopamine release and methamphetamine-stimulated motor activity were significantly lower compared to the control group. These results indicate that H1R blockade at E14-E16 favors the differentiation of dopaminergic neurons, but hampers their migration, leading to a decrease in dopaminergic innervation of the striatum in post-natal life.
ABSTRACT
The hedonic component of the feeding behavior involves the mesolimbic reward system and resembles addictions. Nowadays, the excessive consumption of sucrose is considered addictive. The Wistar-Kyoto (WKY) rat strain is prone to develop anxiety and addiction-like behavior; nevertheless, a lack of information regarding their vulnerability to develop sugar binging-like behavior (SBLB) and how it affects the reward system persist. Therefore, the first aim of the present study was to compare the different predisposition of two rat strains, Wistar (W) and WKY to develop the SBLB in female and male rats. Also, we studied if the SBLB-inducing protocol produces changes in anxiety-like behavior using the plus-maze test (PMT) and, analyzed serotonin (5-HT) and noradrenaline (NA) concentrations in brain areas related to anxiety and ingestive behavior (brain stem, hypothalamus, nucleus accumbens, and amygdala). Finally, we evaluated whether fluoxetine, a drug that has been effective in reducing the binge-eating frequency, body weight, and severity of binge eating disorder, could also block this behavior. Briefly, WKY and W female rats were exposed to 30% sucrose solution (2 h, 3 days/week for 4 weeks), and fed up ad libitum. PMT was performed between the last two test periods. Immediately after the last test where sucrose access was available, rats were decapitated and brain areas extracted for high-performance liquid chromatography analysis. The results showed that both W and WKY female and male rats developed the SBLB. WKY rats consumed more calories and ingested a bigger amount of sucrose solution than their W counterpart. This behavior was reversed by using fluoxetine, rats exposed to the SBLB-inducing protocol presented a rebound effect during the washout period. On female rats, the SBLB-inducing protocol induced changes in NA concentrations on WKY, but not on W rats. No changes were found in 5-HT levels. Finally, animals that developed SBLB showed increased anxiety-like behavior in the PMT. In conclusion, WKY female rats can be considered as a more susceptible rat strain to develop SBLB.
