Ghrelin, a gut-brain peptide hormone, is implicated in a multiplicity of biological functions, including energy homeostasis and reproduction. Neuronal systems that are involved in energy homeostasis as well as reproduction traverse the hypothalamus; however, the mechanism by which they control energy homeostasis is not fully understood. The present study analyzes the anatomical relationship of neurons expressing gonadotropin-releasing hormone (GnRH), neuropeptide Y (NPY) and growth hormone-releasing hormone (GHRH) in a cichlid, tilapia (Oreochromis niloticus). Additionally, we examine in vivo effects of ghrelin on these hypothalamic neurons and plasma growth hormone (GH) and insulin-like growth factor-1 (IGF-1) levels. Double-immunofluorescence showed neuronal fiber associations between GnRH, NPY and GHRH in the brain and pituitary. Intracerebroventricular injection of ghrelin had no effect on numbers, soma size, or optical density of GnRH and NPY neurons, whereas the number of GHRH neurons was significantly decreased in the animals injected with ghrelin when compared to controls, which may indicate administered ghrelin promoted GHRH release. Plasma GH and pituitary GH mRNA levels were significantly increased in the animals injected with ghrelin. These results suggest that central administration of ghrelin primarily act on hypothalamic GHRH neurons to stimulate GH release from the pituitary in the tilapia.
As a natural anti-oxidant source, Tualang honey, produced by wild bees nesting on the Tualang tree (Koompassia excelsa) is expected to have positive influence on health, including memory. This study investigated the effect of Tualang honey on the cell count of memory formation related hippocampal pyramidal neuron and on spatial memory performance (SMP) of rats using the radial arm maze (RAM). Sprague Dawley male rats (n=24), 7-8 weeks old were divided into two groups; experimental group group force-fed 1 mL/100 g body weight with 70% honey (HG); and the control group with 0.9% saline (CG) for 12 weeks. Nissl staining technique (with cresyl violet) was employed for neurohistological analysis of the hippocampal tissue. Six randomly selected rats from each group were used for the neuronal soma counting of pyramidal cell layer CA1, CA3a and CA3c regions. Two-way ANOVA analysis showed positively significant differences between treatment and control groups for SMP comparison of working memory and reference memory components, as well as the number of pyramidal neurons. Hence, this positive effects of Tualang honey, as demonstrated behaviorally and neurohistologically, supported report that Tualang honey could improve memory and deter hippocampal morphological impairments; possibly due to its high anti-oxidant properties.