Electrochemically Driven Photosynthetic Electron Transport in Cyanobacteria Lacking Photosystem II.

Light-activated photosystem II (PSII) carries out the critical step of splitting water in photosynthesis. However, PSII is susceptible to light-induced damage. Here, results are presented from a novel microbial electro-photosynthetic system (MEPS) that uses redox mediators in conjunction with an electrode to drive electron transport in live Synechocystis (ΔpsbB) cells lacking PSII. MEPS-generated, light-dependent current increased with light intensity up to 2050 µmol photons m-2 s-1, which yielded a delivery rate of 113 µmol electrons h-1 mg-chl-1 and an average current density of 150 A m-2 s-1 mg-chl-1. P700+ re-reduction kinetics demonstrated that initial rates exceeded wildtype PSII-driven electron delivery. The electron delivery occurs ahead of the cytochrome b6f complex to enable both NADPH and ATP production. This work demonstrates an electrochemical system that can drive photosynthetic electron transport, provides a platform for photosynthetic foundational studies, and has the potential for improving photosynthetic performance at high light intensities.

Identification of roughskin newt medullary vasotocin target neurons with a fluorescent vasotocin conjugate.

Arginine8 vasotocin (AVT), a neurohypophyseal peptide in nonmammalian vertebrates, plays a key role in the regulation of social behaviors related to reproduction. In male roughskin newts (Taricha granulosa), AVT is an important facilitator of several reproductive behaviors, including courtship clasping of females. Although AVT is known to act in certain brain regions and AVT receptors have been localized to some extent, specific target neurons for this peptide have not been identified in any species. Internalization of a receptor-specific conjugate of AVT and the fluorescent dye Oregon green was used to identify AVT target cells in the medulla of male roughskin newts. Medullary neurons are of interest because they appear to mediate facilitation of clasping by AVT. Direct application of AVT-Oregon green to the fourth ventricular surface of the medulla in vivo resulted in conjugate internalization by a widespread population of medullary neurons, particularly in the medial reticular formation and nuclei of cranial nerves V, VII, VIII, IX, and X. Some fourth-ventricle ependymal cells were also labeled. Reticulospinal neurons, which play an important role in clasping, were identified by retrograde labeling with tetramethylrhodamine dextran amine. AVT-Oregon green was internalized by 72% of these neurons. These results show that AVT can directly affect a very large and diverse medullary neuronal population, which may underlie the peptide's role in multiple neuroendocrinological processes, including autonomic and behavioral regulation. Selectivity of the AVT action may arise through interactions between AVT and steroids such as corticosterone.

Rapid corticosterone-induced impairment of amplectic clasping occurs in the spinal cord of roughskin newts (taricha granulosa).

Courtship clasping, a reproductive behavior in male roughskin newts (Taricha granulosa), is rapidly blocked by an action of corticosterone (CORT) at a specific neuronal membrane receptor. The CORT-induced impairment of clasping in behaving newts appears to be mediated partly by an elimination of clasping-related activity in medullary reticulospinal neurons. Previous studies of rapid CORT actions in Taricha have focused on the brain, so existence of CORT action in the spinal cord or peripheral nervous system has not been assessed. The present study used newts with a high cervical spinal transection to examine potential spinal or peripheral CORT effects on clasping by the hindlimbs in response to pressure on the cloaca. Spinal transection causes clasps elicited by cloacal stimulation to be very sustained beyond the termination of the eliciting stimulus. In spinally transected newts, CORT caused a dose-dependent depression in the duration as well as quality of the clasp that appeared within 10 min of injection. CORT selectively impaired the usual sustained maintenance of a clasp after termination of cloacal stimulation, but not clasp elicitation during stimulation. These effects were not produced by dexamethasone, a synthetic glucocorticoid that binds poorly to the CORT membrane receptor. The CORT effect on clasp maintenance but not clasp elicitation implies selective action on an intraspinal generator for clasping but not on sensory or efferent neuromuscular aspects of the response. These results indicate the presence in the newt spinal cord of the CORT membrane receptor that exerts functional effects distinctly different from those on the brainstem.

Fluorescent vasotocin conjugate for identification of the target cells for brain actions of vasotocin.

The effects of neuropeptides on the brain are a major focus of neuroendocrine research, and little progress has been made in the identification of the target neurons for many neuropeptides. Arginine8-vasotocin (AVT) is a neurohypophyseal peptide present in nonmammalian vertebrates that controls many neural and behavioral functions. Here we describe synthesis and functional characterization of an AVT-Oregon green conjugate 1 (AVT-OG 1) that can be used in vivo to identify AVT target neurons. Application of AVT-OG 1 to the brainstem of an amphibian produces rapid, endosome-like internalization together with typical AVT-like neurophysiological effects. Thus, preparation of AVT-OG 1, which preserves the peptide's neurophysiological effects, is useful as a fluorescent marker for AVT target neurons. Consequently, AVT-OG 1 conjugate will have considerable utility for analyzing the neural actions of AVT in the intact brain.