Wolfgang W. Schwippert

Inhibition of potassium- and acetylcholine-in induced contractions in a molluscan smooth muscle by herbicidal carbamates

Abstract 1. The carbamate herbicide chlorpropham blocks acetylcholine- and potassium-induced tonical contractions of the smooth penis retractor muscle of Helix pomatia L. at concentrations of ≧5 × 10 −6 and ≧10 −5 M , respectively. 2. Reduction of tension development depends on the incubation period and the concentration of the carbamate. 3. The herbicides chlorbufam, barban, propham, and the degradation product 3-chloranilin show comparable effects. 4. The insecticide carbamate carbaryl, which blocks acetylcholinesterase, influences tonical-induced contractions in the opposite way. 5. Inhibition of a Na + -ionophore in the muscle cell membrane by chlorpropham is unlikely.

Visual Integration in Bulbar Structures of Toads: Intra/Extra-Cellular Recording and Labeling Studies

The concept of coding by “command releasing systems” raises the question of how visual information is decoded in post-tectal structures of the medulla oblongata. In the present study, extra- and intracellular activities of neurons in the bulbar reticular formation (RetF) and in nuclei of the branchiomotor column (BMC) were analyzed in response to visual stimulation as well as to electrical stimulation of the optic tectum, the brain stem, or the spinal cord in slightly paralyzed toads. Similarities between tectal and bulbar visual neurons, based on receptive field sizes and responses to moving configurai stimuli, suggest various kinds of integrating properties in the RetF and BMC. Besides configurai selectivities, particular characteristics of bulbar neurons were tonic activity, or warming-up and burst activity in response to specific input. Transformation of a visual input into a standard pre-motor activity was shown by cells that displayed cyclic bursts as a post-stimulus event. Camera-lucida reconstructions of intracellularly labeled neurons revealed five morphological types distinguished by size, orientation, and extension of dendrites. Most labeled cells in the RetF and BMC showed dendritic trees with bewildering arborizations suitable to pick up inputs from different sites of the grey and white matter. Results obtained in amphibians and in mammals are discussed.

The effects of several biocides on a simple muscle preparation of the ecologically relevant soil-organism Lumbricus terrestris L.☆

Abstract 1. The action of different herbicides and one insecticide was studied on the oblique-striated muscle systems of the annelid Lumbricus terrestris L. 2. By means of a simple electrical stimulation device, preparations of the circular muscle system (CMS) were contracted in reproducible manner half-maximally. 3. From 12 tested herbicides, 7 showed a pure inhibiting and one a promoting action, two responded with both effects depending on the duration of incubation and 2 were ineffective. 4. The insecticide pirimicarb, an acetylcholinesterase blocker, enhanced the electrically evoked contractions. 5. The findings coincided in general with those obtained at a defined smooth muscle of the gastropod Helix pomatia L.