Birth order and sibship composition as predictors of overweight or obesity among low-income 4- to 8-year-old children

OBJECTIVE

This study aimed to examine the association of birth order and number and sex of siblings with overweight or obesity among 4- to 8-year-olds.

METHODS

This is a cross-sectional study involving 273 low-income mother-child dyads. Questionnaires and anthropometry were completed. Multiple logistic regression was used to examine the association of birth order, having younger siblings, having older siblings, having at least one brother and having at least one sister with odds of overweight or obesity. Analyses were repeated to additionally include non-biological siblings. Models were adjusted for potential confounders and intermediate variables.

RESULTS

Prevalence of child overweight or obesity was 42.5%. Adjusting for covariates, only children and youngest siblings had higher odds of overweight or obesity compared with oldest siblings (odds ratio [OR]: 4.18, 95% confidence interval [CI]: 1.67, 10.46 and OR: 3.21, 95% CI: 1.41, 7.33, respectively). Having one or more younger siblings and having at least one brother were associated with lower odds (OR: 0.38, 95% CI: 0.21, 0.69 and OR: 0.47, 95% CI: 0.28, 0.81, respectively). Including non-biological siblings did not meaningfully change the associations.

CONCLUSION

Birth order and sibship composition are associated with overweight or obesity among 4- to 8-year-olds. Future studies identifying the underlying behavioural mechanism can help inform family-based intervention programmes.

Reduced SNAP-25 increases PSD-95 mobility and impairs spine morphogenesis

Impairment of synaptic function can lead to neuropsychiatric disorders collectively referred to as synaptopathies. The SNARE protein SNAP-25 is implicated in several brain pathologies and, indeed, brain areas of psychiatric patients often display reduced SNAP-25 expression. It has been recently found that acute downregulation of SNAP-25 in brain slices impairs long-term potentiation; however, the processes through which this occurs are still poorly defined. We show that in vivo acute downregulation of SNAP-25 in CA1 hippocampal region affects spine number. Consistently, hippocampal neurons from SNAP-25 heterozygous mice show reduced densities of dendritic spines and defective PSD-95 dynamics. Finally, we show that, in brain, SNAP-25 is part of a molecular complex including PSD-95 and p140Cap, with p140Cap being capable to bind to both SNAP-25 and PSD-95. These data demonstrate an unexpected role of SNAP-25 in controlling PSD-95 clustering and open the possibility that genetic reductions of the protein levels - as occurring in schizophrenia - may contribute to the pathology through an effect on postsynaptic function and plasticity.

A molecular switch for translational control in taste memory consolidation

In a variety of species memory consolidation following different learning paradigms has been shown to be dependent on protein synthesis. However, it is not known whether modulation of protein synthesis is a critical component of the consolidation process, nor is the identity of any protein(s) subject to translational regulation, known. We report here that phosphorylation of eukaryotic elongation factor-2 (eEF2), an indicator for translational elongation attenuation, is correlated with input that produces taste memory consolidation in the relevant cortex of rat. The temporal pattern of eEF2 phosphorylation is similar to extra-cellular regulated kinase 2 (ERK2) activation and S6K1 phosphorylation, which are known to stimulate translation initiation. In addition, increased eEF2 phosphorylation and increased alphaCaMKII expression is detected in a synaptoneurosomal fraction made from taste cortex following memory consolidation. These results suggest that increased initiation rate together with decreased elongation rate, during memory consolidation, shift the rate-limiting step of protein synthesis, to produce a local switch-like effect in the expression of neuronal proteins.

ERKI/II regulation by the muscarinic acetylcholine receptors in neurons

Muscarinic acetylcholine receptors (mAChRs) are known to be involved in learning and memory, but the molecular basis of their involvement is not well understood. The availability of new and specific biochemical tools has revealed a crucial role for the mitogen-activated protein kinase (MAPK) family in learning and memory. Here, we examine the link between mAChRs and MAPK in neurons. Using the MAPK kinase (MEK)-specific inhibitor PD98059, we first demonstrate a necessary role for active ERKI/II in long-term potentiation in vivo. Using phospho-specific antibodies that recognize the activated form of ERKI/II, we find that the level of ERKI/II activation in brain is regulated by mAChRs. Carbachol, a muscarinic agonist, induces prolonged activation of ERKI/II, without effect on the related kinase SAPK/JNK (stress-activated protein kinase/c-Jun N-terminal protein kinase) in primary cortical cultures. ERKI/II activation is Src-dependent and partially phosphoinositide-3 kinase- and Ca(2+)-dependent but is PKC-independent. M1-M4 mAChR subtypes expressed in COS-7 cells can all induce ERKI/II activation using a signal transduction pathway similar to that operating in neurons. The nature of the signal transduction suggests that ERKI/II can serve as a convergence site for mAChR activation and other neurotransmitter receptors.

Frequency-dependent inhibition in the dentate gyrus is attenuated by the NMDA receptor blocker MK-801 at doses that do not yet affect long-term potentiation

The dual impairment of both long-term potentiation (LTP) in the dentate gyrus and spatial memory by N-methyl-D-aspartate (NMDA) blockers such as 2-aminophosphonovaleric acid (APV) or dizocilpine (MK-801) is considered supportive evidence for the hypothesis that LTP-like mechanisms are involved in spatial memory. However, several studies suggest that, at doses that affect aspects of behavior, LTP is not yet blocked. One possible explanation may be that the blockade of NMDA receptors affect processes other than LTP, which are required for learning. In the present study, we assessed in vivo the effects of the NMDA receptor antagonist MK-801 on LTP and on frequency-dependent inhibition, which has previously been shown to reflect activity of GABAergic interneurons in the rat dentate gyrus. We report here that NMDA receptors are instrumental in frequency-dependent inhibition. Furthermore, frequency-dependent inhibition was found to be more sensitive than LTP to the NMDA antagonist MK-801. Our findings indicate that, in addition to the blockade of LTP, the application of NMDA antagonists affects local circuit activity in the dentate gyrus. The results direct attention to the potential role of interneuronal activity in general and of frequency-dependent inhibition in particular in dentate gyrus related behaviors.

Molecular mechanisms of long-term potentiation in the insular cortex in vivo

We have investigated molecular mechanisms of synaptic plasticity in the pathway between two forebrain structures important for taste learning, the basolateral amygdala (BLA) and the insular cortex. We report here that in vivo long-term potentiation (LTP) induced by BLA stimulation requires functional NMDA receptors and is modulated by muscarinic acetylcholine receptors. In addition, LTP results in the activation of cortical extracellular regulated kinase 1/2 (ERK1/2) and is blocked by inhibitors of ERK1/2 activation. Previous findings demonstrated the involvement of the same molecular mechanisms in the same cortical area during novel taste learning. The results demonstrate that both synaptic and behavioral plasticity share common molecular mechanisms in the insular cortex.

Specific and differential activation of mitogen-activated protein kinase cascades by unfamiliar taste in the insular cortex of the behaving rat

Rats were given to drink an unfamiliar taste solution under conditions that result in long-term memory of that taste. The insular cortex, which contains the taste cortex, was then removed and assayed for activation of mitogen-activated protein kinase (MAPK) cascades by using antibodies to the activated forms of various MAPKs. Extracellular responsive kinase 1-2 (ERK1-2) in the cortical homogenate was significantly activated within <30 min of drinking the taste solution, without alteration in the total level of the ERK1-2 proteins. The activity subsided to basal levels within <60 min. In contrast, ERK1-2 was not activated when the taste was made familiar. The effect of the unfamiliar taste was specific to the insular cortex. Jun N-terminal kinase 1-2 (JNK1-2) was activated by drinking the taste but with a delayed time course, whereas the activity of Akt kinase and p38MAPK remained unchanged. Elk-1, a member of the ternary complex factor and an ERK/JNK downstream substrate, was activated with a time course similar to that of ERK1-2. Microinjection of a reversible inhibitor of MAPK/ERK kinase into the insular cortex shortly before exposure to the novel taste in a conditioned taste aversion training paradigm attenuated long-term taste aversion memory without significantly affecting short-term memory or the sensory, motor, and motivational faculties required to express long-term taste aversion memory. It was concluded that ERK and JNK are specifically and differentially activated in the insular cortex after exposure to a novel taste, and that this activation is required for consolidation of long-term taste memory.

Lateral ventricle injection of the protein synthesis inhibitor anisomycin impairs long-term memory in a spatial memory task

Although protein synthesis inhibition has been shown to affect long-term memory in a wide variety of animal species, cases have been reported in which protein synthesis inhibition failed to affect memory consolidation [S. Wittstock, R. Menzel, Color learning and memory in honey bees are not affected by protein synthesis inhibition, Behav. Neural Biol., 62 (1994) 224-229.]. Most findings argue that the critical time for protein synthesis is during or immediately after training. However, other reports show a second time window, hours after training, where protein synthesis inhibition can cause amnesia [F.M. Freeman, S.P.R. Rose, A.B. Scholey, Two time windows of anisomycin-induced amnesia for passive avoidance training in the day-old chick, Neurobiol. Learn. Mem., 63 (1995) 291-295.][G. Grecksch, H. Matthies, Two sensitive periods for the amnesic effect of anisomycin, Pharmacol. Biochem. Behav., 12 (1980) 663-665.]. In this study, we addressed two questions: (1) Is protein synthesis essential for spatial memory? and (2) At what injection time window(s) will protein synthesis inhibition cause spatial memory amnesia? We report that bilateral intraventricular microinjection of anisomycin (Ani) impairs consolidation of long-term memory, in the hippocampal-dependent Morris water maze spatial memory task. Memory was impaired in a dose-dependent manner without affecting short-term memory. Spatial memory was affected only if Ani was injected 20 min before performing the task and not in any other time window before or after the behavioral test. The inhibition did not affect pre-existing memories or the capability to memorize once the effect of the inhibition diminished.

NMDA receptor and the tyrosine phosphorylation of its 2B subunit in taste learning in the rat insular cortex

We demonstrate that the NMDA receptor is involved in taste learning in the insular cortex of the behaving rat and describe two facets of this involvement. Blockage of the NMDA receptor in the insular cortex by the reversible antagonist APV during training in a conditioned taste aversion (CTA) paradigm impaired CTA memory, whereas blockage of the NMDA receptor in an adjacent cortex or before a retrieval test had no effect. When rats sampled an unfamiliar taste and hence learned about it, either incidentally or in the context of CTA training, the tyrosine phosphorylation of the NMDA receptor subunit 2B (NR2B) in the insular cortex was specifically increased. The level of tyrosine phosphorylation on NR2B was a function of the novelty of the taste stimulus and the quantity of the taste substance consumed, properties that also determined the efficacy of the taste stimulus as a conditioned stimulus in CTA; however, blockage of the NMDA receptor by APV during training did not prevent tyrosine phosphorylation of NR2B. We suggest that tyrosine phosphorylation of NR2B subserves encoding of saliency in the insular cortex during the first hours after an unfamiliar taste is sampled and that this encoding is independent of another, necessary role of NMDA receptors in triggering experience-dependent modifications in the insular cortex during taste learning. Because a substantial fraction of the NR2B protein in the insular cortex seems to be expressed in interneurons, saliency and the tyrosine phosphorylation of NR2B correlated with it may modulate inhibition in cortex.

Long-term potentiation increases tyrosine phosphorylation of the N-methyl-D-aspartate receptor subunit 2B in rat dentate gyrus in vivo

Long-term potentiation (LTP) is a form of synaptic memory that may subserve developmental and behavioral plasticity. An intensively investigated form of LTP is dependent upon N-methyl-D-aspartate (NMDA) receptors and can be elicited in the dentate gyrus and hippocampal CA1. Induction of this type of LTP is triggered by influx of Ca2+ through activated NMDA receptors, but the downstream mechanisms of induction, and even more so of LTP maintenance, remain controversial. It has been reported that the function of NMDA receptor channel can be regulated by protein tyrosine kinases and protein phosphatases and that inhibition of protein tyrosine kinases impairs induction of LTP. Herein we report that LTP in the dentate gyrus is specifically correlated with tyrosine phosphorylation of the NMDA receptor subunit 2B in an NMDA receptor-dependent manner. The effect is observed with a delay of several minutes after LTP induction and persists in vivo for several hours. The potential relevance of this post-translational modification to mechanisms of LTP and circuit plasticity is discussed.

Carbachol mimics effects of sensory input on tyrosine phosphorylation in cortex

We have recently shown that in the gustatory cortex of the rat, taste learning enhances protein tyrosine phosphorylation and taste memory is blocked by muscarinic antagonists. A major protein whose tyrosine phosphorylation is stimulated by taste learning in cortex is a 180 kDa synaptic glycoprotein identified as the NMDA receptor subunit 2B (NR2B). Here we report that microinjection of carbachol into the taste cortex modulates protein tyrosine phosphorylation similarly to the effect of unfamiliar taste, and that a 180 kDa protein whose tyrosine phosphorylation is enhanced in vivo by carbachol is NR2B. These data, combined with our previous findings, are in line with the hypothesis that muscarinic input plays a role in encoding new items in memory, and that tyrosine phosphorylation of NR2B is involved in this process.

Modulation of protein tyrosine phosphorylation in rat insular cortex after conditioned taste aversion training

Protein tyrosine phosphorylation is a major signal transduction pathway involved in cellular metabolism, growth, and differentiation. Recent data indicate that tyrosine phosphorylation also plays a role in neuronal plasticity. We are using conditioned taste aversion, a fast and robust associative learning paradigm subserved among other brain areas by the insular cortex, to investigate molecular correlates of learning and memory in the rat cortex. In conditioned taste aversion, rats learn to associate a novel taste (e.g., saccharin) with delayed poisoning (e.g., by LiCl injection). Here we report that after conditioned taste aversion training, there is a rapid and marked increase in tyrosine phosphorylation of a set of proteins in the insular cortex but not in other brain areas. A major protein so modulated, of 180 kDa, is abundant in a membrane fraction and remains modulated for more than an hour after training. Exposure of the rats to the novel taste alone results in only a small modulation of the aforementioned proteins whereas administration of the malaise-inducing agent per se has no effect. To the best of our knowledge, this is the first demonstration of modulation of protein tyrosine phosphorylation in the brain after a behavioral experience.

Overexpression of urokinase-type plasminogen activator in transgenic mice is correlated with impaired learning

Transgenic mice designated alpha MUPA overproduce in the brain murine urokinase-type plasminogen activator (uPA), an extracellular protease implicated in tissue remodeling. We have now localized, by in situ hybridization, extensive signal of uPA mRNA in the alpha MUPA cortex, hippocampus, and amygdala, sites that were not labeled in counterpart wild-type mice. Furthermore, biochemical measurements reveal a remarkably high level of enzymatic activity of uPA in the cortex and hippocampus of alpha MUPA compared with wild-type mice. We have used the alpha MUPA mice to examine whether the abnormal level of uPA in the cortex and the limbic system affects learning ability. We report that alpha MUPA mice perform poorly in tasks of spatial, olfactory, and taste-aversion learning, while displaying normal sensory and motor capabilities. Our results suggest that uPA is involved in neural processes subserving a variety of learning types.

Taste memory: the role of protein synthesis in gustatory cortex

Application of the protein synthesis inhibitor anisomycin to the rat gustatory cortex before and during training impairs conditioned taste aversion (CTA) to saccharin. No behavioral impairment is observed if the inhibitor is applied to an adjacent cortical area or to one cortical hemisphere only. The consumption of saccharin and of total fluid, as well as behavioral recognition of saccharin, is not affected. Preexposure of rats to saccharin several days before training markedly inhibits CTA to that taste. Injection of anisomycin to the gustatory cortex immediately prior to the preexposure period attenuates the latent inhibition. These results suggest that protein synthesis in the gustatory cortex is required for normal acquisition of the memory of taste.