The morphological changes undergone by the osteoblast at the ultrastructural level, during its differentiation into osteocyte, were studied in the primary parallel-fibred bone of the newborn rabbit by means of incomplete three-dimensional reconstruction from partially serial-sectioned preosteocytes. The findings obtained suggest that the formation of osteocyte cytoplasmic processes is an asynchronous and asymmetrical phenomenon that seems to precede the mineralization of the organic matrix and to give rise to an asymmetrical mature osteocyte. The functions of cytoplasmic processes as regards bone formation, cell nutrition and osteoblast modulation are discussed. The mechanism by which the osteoblast ‘enters’ the bone matrix is hypothesized.

A vagus nerve–mediated, brain cholinergic protective mechanism activated by melanocortin peptides is operative in conditions of circulatory shock; moreover, there is anatomical evidence of dual vagal-cardiac efferent pathways in rats, which could play different roles in controlling heart function. Therefore, we investigated the role and functional mechanism of such vagal efferent pathway(s) in an experimental model of ischemic heart disease. Randomized experimental study. Research laboratory. Adult Wistar rats of either sex. After bilateral cervical vagotomy (with or without pretreatment with atropine), efferent vagal fibers were electrically stimulated in rats subjected to coronary artery occlusion (5 mins) followed by reperfusion (5 mins). Other rats (intact, vagotomized, or pretreated with atropine) were treated with nanomolar doses of melanocortin peptides. Electrical stimulation of efferent vagal fibers (5 V, 2 msecs, 1–9 Hz, for the whole period of ischemia/reperfusion) strongly reduced the high incidence of severe arrhythmias and lethality, reduced the increase in free radical blood levels and left-ventricle histologic alterations, and augmented the extracellular signal–regulated kinase activation. Treatment with the melanocortin peptides adrenocorticotropin and γ2-melanocyte-stimulating hormone (162 nmol/kg intravenously or 16.2 nmol/kg intracerebroventricularly, during coronary occlusion) produced the same protective effects of electrical stimulation and with the same muscarinic acetylcholine receptor–dependent mechanism, seemingly through brain activation (mediated by melanocortin MC3 receptors, as previously described) of such efferent vagal pathway. The present results give evidence for the identification of a protective, melanocortin-activated, efferent vagal cholinergic pathway, operative in conditions of myocardial ischemia/reperfusion. These data suggest that melanocortins and pertinent compounds able to activate such a pathway could provide the potential for development of a new class of drugs for a novel approach to management of ischemic heart disease.

Ischemic stroke is one of the main causes of death and disability. We investigated whether melanocortin peptides, which have protective effects in severe hypoxic conditions, also produce neuroprotection in a gerbil model of ischemic stroke. A 10-min period of global cerebral ischemia, induced by occluding both common carotid arteries, caused impairment in spatial learning and memory that was associated with activation of inflammatory and apoptotic pathways, including severe DNA damage and delayed neuronal death, in the hippocampus. Treatment with nanomolar doses of the melanocortin analog [Nle⁴, d-Phe⁷] α-MSH [which activates the melanocortin receptor subtypes (MC) mainly expressed in central nervous system, namely MC₃ and MC₄] modulated the inflammatory and apoptotic cascades and reduced hippocampus injuries even when delayed up to 9 h after ischemia, with consequent dose-dependent improvement in subsequent functional recovery. The selective MC₃ receptor agonist γ₂-MSH had no protective effects. Pharmacological blockade of MC₄ receptors prevented the neuroprotective effects of [Nle⁴, d-Phe⁷] α-MSH and worsened some ischemia outcomes. Together, our findings suggest that MC₄ receptor-stimulating melanocortins might provide potential to develop a class of drugs with a broad treatment window for a novel approach to neuroprotection in ischemic stroke.