Central Opioidergic System Interplay with Histamine on Food Intake in Neonatal Chicks: Role of µ-Opioid and H1/H3 Receptors

The role of central neurotransmitters in appetite regulation of broilers and layers: similarities and differences

The importance of feeding as a vital physiological function, on the one hand, and the spread of complications induced by its disorder in humans and animals, on the other hand, have led to extensive research on its regulatory factors. Unfortunately, despite many studies focused on appetite, only limited experiments have been conducted on avian, and our knowledge of this species is scant. Considering this, the purpose of this review article is to examine the role of central neurotransmitters in regulating food consumption in broilers and layers and highlight the similarities and differences between these two strains. The methodology of this review study includes a comprehensive search of relevant literature on the topic using appropriate keywords in reliable electronic databases. Based on the findings, the central effect of most neurotransmitters on the feeding of broilers and laying chickens was similar, but in some cases, such as dopamine, ghrelin, nitric oxide, and agouti-related peptide, differences were observed. Also, the lack of conducting a study on the role of some neurotransmitters in one of the bird strains made it impossible to make an exact comparison. Finally, it seems that although there are general similarities in appetite regulatory mechanisms in meat and egg-type chickens, the long-term genetic selection appropriate to breeding goals (meat or egg production) has caused differences in the effect of some neurotransmitters. Undoubtedly, conducting future studies while completing the missing links can lead to a comprehensive understanding of this process and its manipulation according to the breeding purposes of chickens.

Exogenous histamine and H 2 receptor activation and H 3 receptor inhibition in nucleus accumbens modulate formalin-induced orofacial nociception through opioid receptors

It has been demonstrated that the nucleus accumbens (NAc) plays an important role in modulation of nociception due to its extensive connections with different regions of the brain. In addition, this nucleus receives histaminergic projections from tuberomammillary nucleus. Considering the role of the central histaminergic system in nociception, the effect of histamine and its H 2 and H 3 receptors agonist and antagonist microinjections into the NAc on orofacial formalin nociception was investigated. In male Wistar rats, using stereotaxic surgery, two guide cannulas were bilaterally implanted into the right and left sides of the NAc. Diluted formalin solution (1.5%, 50 µl) injection into the vibrissa pad led to orofacial nociception. Immediately after injection, face rubbing was observed at 3-min blocks for 45 min. Orofacial formalin nociception was characterized by a biphasic nociceptive response (first phase: 0-3 min and second phase: 15-33 min). Microinjections of histamine (0.5 and 1 μg/site), dimaprit (1 μg/site, H 2 receptor agonist) and thioperamide (2 μg/site, H 3 receptor antagonist) attenuated both phases of formalin orofacial nociception. Prior microinjection of famotidine (2 μg/site) inhibited the antinociceptive effects of dimaprit (1 μg/site). Furthermore, comicroinjection of thioperamide (2 μg/site) and immepip (1 μg/site) prevented thioperamide (2 μg/site)-induced antinociception. Naloxone (2 μg/site) also prevented histamine, dimaprit- and thioperamide-induced antinociception. The results of this study demonstrate that at the level of the NAc, histamine and its H 2 and H 3 receptors are probably involved in the modulation of orofacial nociception with an opioid system-dependent mechanism.

Central effects of opioidergic system on food intake in birds and mammals: a review

Undoubtedly, the food intake process is one of the most necessary physiological functions for the survival of animals and humans. Although; this operation seems simple on the surface, the regulation of the mechanisms involved in it requires the cooperation of many neurotransmitters, peptides, and hormonal factors in the nervous and endocrine systems. Understanding the signals that regulate energy levels and appetite, may open new approaches to therapeutics and drugs used in obesity-related complications. Improving the quality of animal products and health is also possible due to this research. The present review is aimed to sum up the current findings on central effects of opioids on the food consumption of birds and mammals. Based on the reviewed articles, the opioidergic system appears to be one of the key elements in the birds' and mammals' food intake and is closely related to other systems involved in appetite regulation. According to the findings, it seems that the effects of this system on nutritional mechanisms are often applied via kappa- and mu-opioid receptors. Controversial observations have been made regarding opioid receptors, highlighting the need for further studies, especially at the molecular level. The role of opiates in taste or diet craving also showed the efficacy of this system, especially the mu-opioid receptor, on preferences such as diets containing high sugar and fat. Finally, putting the results of this study together with the findings of human experiments and other primates can lead to a correct comprehension of the appetite regulation processes, especially the role of the opioidergic system.