Improved neurochemical recovery of 6-hydroxydopamine-lesioned postganglionic sympathetic neurons by nerve growth factor in the adult rat

Early, selective, and marked loss of sympathetic nerves from the islets of BioBreeder diabetic rats

To discover whether islet sympathetic nerves are damaged during the autoimmune destruction of islet B-cells, we immunostained sections of pancreas from BioBreeder (BB) diabetic rats, using antibodies against vesicular monoamine transporter 2 (VMAT2), a marker of sympathetic nerve terminals. We found a marked decrease in the VMAT2-positive fiber area in the islets of BB rats that had been diabetic for only 1-2 weeks compared with their nondiabetic controls. In contrast, there was no significant decrease in the VMAT2-positive fiber area in the exocrine pancreas in these early diabetic BB rats. Furthermore, streptozotocin-diabetic rats showed no decrease in VMAT2-positive fiber area in their islets compared with controls. The classical diabetic autonomic neuropathy (DAN) that eventually occurs in the heart was not present in BB diabetic rats at this early stage as evidenced by normal cardiac VMAT2 immunostaining and normal cardiac norepinephrine content. Also, in contrast to DAN, this islet neuropathy did not worsen with duration of diabetes. These data provide evidence of a heretofore unrecognized early sympathetic islet neuropathy (eSIN). Because eSIN occurs selectively in the islet, is rapid in onset, and is associated with autoimmune but not chemically induced diabetes, it is distinct from DAN in location, time course, and mechanism.

Cholecystokinin-8 promotes recovery of sympathectomy induced by 6-hydroxydopamine in adult mice

We used an experimental model of sympathetic neuropathy to investigate the effects of intraperitoneal cholecystokinin-8 (CCK-8) administration on the recovery of injured peripheral neurones. After treatment of adult mice with 6-hydroxydopamine (6-OHDA), which known to induce peripheral sympathectomy, nerve growth factor (NGF) in peripheral tissue first increased and then rapidly decreased to baseline levels. Following this observation, sympathectomised mice were treated with CCK-8 starting when the NGF levels lowered toward the control value. Our results show that injections with 8 nmol/kg of CCK-8 promote not only recovery of noradrenergic innervation but also NGF and neuropeptide Y (NPY) synthesis in peripheral tissue. This latter observation suggests that the effect of CCK-8 might be mediated through the stimulation of NGF synthesis.

Cholecystokinin-8 enhances nerve growth factor synthesis and promotes recovery of capsaicin-induced sensory deficit

Alterations of nerve growth factor (NGF) expression have been demonstrated during peripheral nerve disease and the impaired expression or synthesis and transportation of NGF has been correlated with the pathogenesis of several peripheral neuropathies. Since exogenous NGF administration seems to cause undesired side-effects, therapeutical strategies based on the regulation of endogenous synthesis of NGF could prove useful in the clinical treatment of these disorders. The aim of the present study was to analyse the effects of exogenous peripheral administration of the neuropeptide cholecystokinin-8 (CCK-8) on endogenous NGF synthesis, NGF mRNA and distribution of peripheral neuropeptides which are known to be regulated by this neurotrophin. To address these questions we studied the effects of capsaicin (CAPS) before and after the administration of CCK-8 on NGF levels, NGF mRNA expression and localization, and the concentration of substance P (SP) and calcitonin gene-related peptide (CGRP) in peripheral tissue These studies demonstrate that administration of the CCK-8 induces an increase of NGF protein and mRNA in peripheral tissue. NGF level in paw skin of CAPS/CCK-8-treated mice is 3 fold higher than in controls (1241+/-110 pg gr(-1) of tissue wet weight versus 414+/-110 pg gr(-1) of controls) and nearly 6 fold higher than in CAPS-treated mice (1241+/-110 pg gr(-1) versus 248+/-27 pg gr(-1)). The increase of NGF is correlated with the recovery of impaired nocifensive behaviour and with an overexpression of SP and CGRP. The evidence that CCK-8 promotes the recovery of sensory deficits suggests a potential clinical use for this neuropeptide in peripheral neuropathies.