PAC1 receptor localization in a model nervous system: light and electron microscopic immunocytochemistry on the earthworm ventral nerve cord ganglia

The presence and pattern of pituitary adenylate cyclase activating polypeptide (PACAP) type I (PAC1) receptors were identified by means of pre- and post-embedding immunocytochemical methods in the ventral nerve cord ganglia (VNC) of the earthworm Eisenia fetida. Light and electron microscopic observations revealed the exact anatomical positions of labeled structures suggesting that PACAP mediates the activity of some interneurons, a few small motoneurons and certain sensory fibers that are located in ventrolateral, ventromedial and intermediomedial sensory longitudinal axon bundles of the VNC ganglia. No labeling was located on large interneuronal systems such as dorsal medial and lateral giant axon systems and ventral giant axons. At the ultrastructural level labeling was mainly restricted to endo- and plasma membranes showing characteristic unequal distribution in various neuron parts. An increasing abundance of PAC1 receptors located on both rough endoplasmic reticulum and plasma membranes was seen from perikarya to neural processes, indicating that intracellular membrane traffic might play a crucial role in the transportation of PAC1 receptors. High number of PAC1 receptors was found in both pre- and postsynaptic membranes in addition to extrasynaptic sites suggesting that PACAP acts as neurotransmitter and neuromodulator in the earthworm nervous system.     

Effects of PACAP on in vitro and in vivo neuronal cell death, platelet aggregation, and production of reactive oxygen radicals

Pituitary adenylate cyclase activating polypeptide (PACAP) exerts neuroprotective effects in various in vitro and in vivo models of cerebral pathologies. It has been shown that PACAP protects neurons in rat models of both global and focal ischemia. In the present study, we investigated factors that may play a role in the neuroprotective effects of PACAP. PACAP strongly reduced the anisomycin-induced apoptosis of PC12 cells, which was abolished in a PKA-deficient PC12 cell line (A126). This effect was also observed in vivo, in permanent occlusion of the middle cerebral artery, where the number of TUNEL-positive neurons was significantly reduced in the ischemic core of PACAP-treated animals. Our results show that PACAP has a minor antioxidant effect in a non-cellular in vitro system, and has considerable antioxidant effects in an in vitro red blood cell filtration model. PACAP had no effect on platelet aggregation induced by collagen, ADP or epinephrine. Our results demonstrate that the effects of PACAP on delayed neuronal death may play a significant role in the reduction of the infarct size in vivo, but the antioxidant effect could only be observed at concentrations higher than that used in the model of focal ischemia.     

Preconditioning with volatile anaesthetic sevoflurane in ischemic retinal lesion in rats

Volatile anaesthetic agents have been recognized for their neuroprotective properties since the 1960s. However, little is known regarding the potential retinoprotective effects of preconditioning by anaesthetic drugs. Retinal ischemia can be modeled by permanent bilateral common carotid artery occlusion (BCCAO). Here we studied the degree of ischemic injury with preconditioning by sevoflurane in the rat retina. During the BCCAO operation and preconditioning Wistar rats were anaesthetized with 1 MAC of sevoflurane. The oxygen, carbon dioxide, and anaesthetic vapor concentration in the anaesthetizing box was monitored with a gas analyzer. We examined 4 groups: non- and preconditioning groups in control and BCCAO animals. The duration of preconditioning period was 1?h and it was performed 1?day before BCCAO. The retinas were processed for histological evaluation after 2?weeks survival to determine the cell number in the ganglion cell layer and the thickness of the whole retina and that of all retinal layers. BCCAO-induced retinal ischemic injury was ameliorated by sevoflurane preconditioning. Retinal thickness and the cell number in the ganglion cell layer were more retained in preconditioned animals after BCCAO compared to non-preconditioned group. These results suggest that preconditioning using sevoflurane could provide a new perspective in retinoprotective strategies.