Despite possessing a limited number of neurones compared to vertebrates, honeybees show remarkable learning and memory performance, an example being 'dance communication'. In this phenomenon, foraging honeybees learn the location of a newly discovered food source and transmit the information to nestmates by symbolic abdomen vibrating behaviour, leading to navigation of nestmates to the new food source. As an initial step toward understanding the detailed molecular mechanisms underlying the sophisticated learning and memory performance of the honeybee, we focused on the neural immediate early genes (IEGs), which are specific genes quickly transcribed after neural activity without de novo protein synthesis. Although these have been reported to play an essential role in learning and memory processes in vertebrates, far fewer studies have been performed in insects in this regard. From RNA-sequencing analysis and subsequent assays, we identified three genes, Src homology 3 (SH3) domain binding kinase, family with sequence similarity 46 and GB47136, as novel neural IEGs in the honeybee. Foragers and/or orientating bees, which fly around their hives to memorize the positional information, showed induced expression of these IEGs in the mushroom body, a higher-order centre essential for learning and memory, indicating a possible role for the novel IEGs in foraging-related learning and memory processes in the honeybee.
Functional maturation of the small intestine occurs during the weaning period in rats. It is known that this development is facilitated by glucocorticoid. However, the effect of glucocorticoid on morphological development of small intestine has yet to be clarified. The present study evaluated the morphological development and cell proliferation of the small intestine in adrenalectomized (ADX) rat pups. To further understand the mechanism of glucocorticoid effects on intestinal development, we examined the localization of the glucocorticoid receptor in the small intestine. Microscopic analysis showed that growth of villi and crypts is agedependent, and is significantly attenuated in ADX rats compared with sham-operated rats. BrdU-positive cells, i.e. proliferating cells, were primarily observed in crypt compartments and rapidly increased in number during the early weaning period. The increase in BrdUpositive cells could be attenuated by adrenalectomy. The morphological development of small intestine may be associated with increased proliferation of epithelial cells. On the other hand, glucocorticoid receptors were found in epithelial cells of the mid-and lower villi and not in crypts where BrdU-positive cells were localized. These results indicate that the growth of small intestine is attenuated by adrenalectomy, and that glucocorticoid indirectly acts on proliferation of epithelial cells during the weaning period.
Feeding behavior is regulated by feeding-related peptides in the hypothalamus. The neurons of the arcuate nucleus (ARC), which produces feeding-related peptides, develop and function by three weeks of age in rodents. Because rodents are weaned at three weeks, we studied whether the process of weaning is involved in the development of ARC neurons using monosodium glutamate. Rat pups injected neonatally with monosodium glutamate ingested a large amount of mother's milk at weaning. Monosodium glutamate treatment induced a decrease in the number of ARC cells and mRNA levels of neuropeptide Y and agouti-related protein in the hypothalamus. The alteration of milk consumption following monosodium glutamate treatment appears to cause failure of ARC neuron development and neuropeptide expression.
E#ect of fenfluramine on nipple attachment in rat pups at weaning. Suckling behavior test was performed at +/, ,* and ,/ days after birth. Data were expressed as mean (ῑSD) of attachment time during a 0* min test. * P*.*/, compared with saline administrated rats. E#ect of metergoline on nipple attachment in rat pups at weaning. Suckling behavior test was performed at +/, ,* and ,/ days after birth. Data were expressed as mean (ῑSD) of attachment time during a 0* min test. * Pῒ*.*/, compared with vehicle administrated rats. E#ect of metergoline (+ mg/kg) and fenfluramine (+* mg/kg) on nipple attachment in rat pups at weaning. Suckling behavior test was performed at +/, ,* and ,/ days after birth. Data were expressed as mean (ῑSD) of attachment time during a 0* min test. * Pῒ*.*/, compared with vehicle and saline administrated rats. ΐ Pῒ*.*/, compared with only fenfluramine administrated rats. Identification of a /-HT+ recognition site in human brain membranes di#erent from /-HT+A, /-HT+B and /-HT+C sites. Neuroscience Letters, 2/ : -/1ῌ-0,. Jongsma ME, Sebens JB, Bosker FJ, Korf J. ,**,. E#ect of /-HT+A receptor-mediated serotonin augmentation on Fos immunoreactivity in rat brain. Corresponding : Tohru MIYATA (fax : ῌ2+ (*) .,ῌ1-3ῌ22/., e-mail : mytto.acῌagr.tamagawa.ac.jp) QῌQQῌQQῌQ´ QQ̲QThe serotonergic nervous system is known to participate in the regulation of feeding behavior and in the selective control of feeding patterns. However, the correlation between central serotonergic function and feeding transition of weaning has not been well documented. To evaluate the involvement of the serotoneric nervous system in weaning, we investigated the e#ect of serotonergic medication on suckling behavior and feeding patterns in rat pups during the weaning period. Rat pups were injected with +, /, 1./ and +* mg/kg of fenfluramine, an inducer of serotonin release, or +, / and +* mg/kg of metergoline, a /-HT+ and /-HT, receptor antagonist, and duration of nipple attachment to the anesthetized dam was recorded as a measure of suckling behavior. Fenfluramine injection produced a dose-dependent decrease in the duration of nipple attachment. Treatment with metergoline increased duration of attachment even at the lowest dose. The inhibitory e#ect on suckling behavior of fenfluramine was attenuated by pretreatment with metergoline.Moreover, metergoline-injected rats preferred suckling behavior over eating solid food. Therefore, it may be possible that the serotonergic nervous system not only influences the regulation of suckling behavior but also feeding selectivity associated with the weaning process.
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