Plasma cholinesterase activity: A benchmark for rapid detection of pesticide poisoning in an avian scavenger.

Poisoning due to exposure to organophosphate and carbamate pesticides is a common threat for many wildlife species, especially for scavengers such as vultures. The Griffon vulture population (Gyps fulvus), for instance, is deteriorating in the Eastern Mediterranean, and is considered to be critically endangered in Israel, where 48 out of 107 (45 %) known injury/mortality cases in 2010-2021 were caused by poisoning. Lack of specific clinical indications, together with levels of organophosphate or carbamate pesticides too low to detect, challenge the ability to diagnose and treat such poisoning events. The activity of cholinesterase (ChE) in plasma has the potential to serve as an effective biomarker for monitoring exposure to anticholinesterase pesticides in live vultures. Yet, the applicability of this approach has been limited by intra- and inter-species variations in ChE basal levels. The present study aims to provide a benchmark for ChE activity levels in healthy Griffons and their intra-species variation. Blood samples from free-roaming (n = 231) and captive (n = 63) Griffons were collected during routine monitoring, and ChE levels were determined using a colorimetric method. We established that the ChE in the plasma of Griffons reflects mostly acetylcholinesterase as the dominant form. ChE levels in healthy Griffons are 0.601 ± 0.011 U/ml (mean ± SE), while Griffons with suspected or confirmed pesticide poisoning display much lower levels of ChE activity (typically <0.3 U/ml). We also characterized the age dependence of ChE activity, as well as differences among groups from different locations or origins. Our study provides a rapid diagnostic tool for the detection of exposure to organophosphate and carbamate pesticides that should facilitate the lifesaving treatment and the conservation of this species. Moreover, our protocols can be adapted to other species and geographical areas, addressing pesticide poisoning worldwide and contributing to the protection of endangered species and their ecological functions (e.g. sanitation by scavengers).

Fine Localization of Acetylcholinesterase in the Synaptic Cleft of the Vertebrate Neuromuscular Junction.

Acetylcholinesterase (AChE) is concentrated at cholinergic synapses, where it is a major factor in controlling the duration of transmitter action. The concentration and localization of AChE within the synaptic cleft are in keeping with the functional requirements of the particular type of synapse. The densities of synaptic AChE at various neuromuscular junctions (NMJs) had been evaluated by quantitative EM-autoradiography using radiolabeled probes. Yet, fundamental issues concerning the precise distribution and location of the enzyme in the cleft remained open: whether and to what extent synaptic AChE is associated with pre- or postsynaptic membranes, or with synaptic basal lamina (BL), and whether it occurs only in the primary cleft (PC) or also in postjunctional folds (PJFs). Nanogold-conjugates of fasciculin, an anticholinesterase polypeptide toxin, were prepared and used to label AChE at NMJs of mouse and frog muscles. Selective intense labeling was obtained at the NMJs, with gold-labeled AChE sites distributed over the BL in the PC and the PJFs. Quantitative analysis demonstrated that AChE sites are almost exclusively located on the BL rather than on pre- or postsynaptic membranes and are distributed in the PC and down the PJFs, with a defined pattern. This localization pattern of AChE is suggested to ensure full hydrolysis of acetylcholine (ACh) bouncing off receptors, thus eliminating its unnecessary detrimental reattachment.