Activities of mesencephalic nucleus neurons during fictive swimming of the carp Cyprinus carpio

ABSTRACT:   Fish swim by undulatory contractions of the axial trunk musculature. It has been presumed that a descending signal from the brainstem activates central pattern generators in the spinal cord to make the swimming rhythm. In the carp the electrical or chemical stimulation of a mesencephalic nucleus, the nucleus fasciculi longitudinalis medialis (Nflm), could initiate swimming. However, it has not been established what signals originate from the Nflm in order to make the fish swim. The activity of the Nflm neurons was therefore examined electrophysiologically during fictive swimming in paralyzed carp. Three types of neuronal activities closely related to the swimming rhythms were obtained. The first type was a continuous tonic firing throughout an episode of fictive swimming. Neurons involved in this tonic activity may project to the spinal cord and contribute to the activation of spinal neurons to initiate fish swimming. The second type was accompanied by continual phasic firings occurring in rhythm with the activity of spinal motoneurons. Supposing that the swimming rhythm originates in the spinal cord, the synchronous activity in the brain neurons may suggest that in the nucleus there is a relay neuron conveying the rhythm information from the cord to other neurons there or in the brain. The third type exhibited reduced firing rates during fictive swimming. It is possible that the neurons engaged in this activity may be inhibitory and suppress the activities of other neurons in the nucleus and spinal cord during rest or during decelerating swimming.     

A new method for recording activities of spinal motoneurons during fictive swimming in paralyzed teleost fish

ABSTRACT: A new method for monitoring spinal motoneuron activities during fictive swimming in teleost fish was developed. Enamel-insulated copper wire electrodes were implanted in the trunk muscle of goldfish or carp. For each freely moving fish, an electromyogram (EMG) was recorded using the electrodes. In those fish paralyzed with curare, using the same electrode set, bursts of electrical activities consisted of spikes of smaller amplitude and of shorter duration compared with those recorded by EMG. Simultaneous recording of the extracellular activity and intracellular recording from the muscle revealed that the bursts of spikes recorded in the paralyzed fish were motor nerve impulses innervating the muscle and are considered to be fictive swimming activity. The method developed in the present study provides a useful tool with which to investigate neuronal mechanisms underlying swimming activity in teleost fish.     

Weed control with alfalfa pellets in transplanting rice

Alfalfa [ Medicago sativa L. ( M. media , M. falcate )] plants contain allelochemicals that have detrimental effects on their own growth and that of surrounding plants. Alfalfa pellets, used as a food for livestock, were used as the material for the control of weeds in this study. In a greenhouse experiment, alfalfa pellets applied at 1–3 tons ha⁻¹ completely inhibited the emergence of abunome ( Doparium junceum Hamilt.), false pimpernel ( Lindernia pyxidaria L.), and long stemmed water wort ( Elatine trianda Schk. var. pedicellata Krylov) The number and the dry weight of emerged Echinochloa oryzicola plants were significantly reduced. Application of 3 tons ha⁻¹ alfalfa pellets completely inhibited the emergences of Eleocharis acicularis and Rotala indica. Results demonstrated that the inhibitory effect of alfalfa pellets became greater as the dose increased, and it also varied among weed species. Furthermore, the paddy field experiment suggested that the dose of 1–2 tons ha⁻¹ of alfalfa pellets could control more weed species without any rice plant injury.