Specialized brain regions and sensory inputs that control locomotion in leeches

Abstract

Locomotor systems are often controlled by specialized cephalic neurons and undergo modulation by sensory inputs. In many species, dedicated brain regions initiate and maintain behavior and set the duration and frequency of the locomotor episode. In the leech, removing the entire head brain enhances swimming, but the individual roles of its components, the supra- and subesophageal ganglia, in the control of locomotion are unknown. Here we describe the influence of these two structures and that of the tail brain on rhythmic swimming in isolated nerve cord preparations and in nearly-intact leeches suspended in an aqueous, “swim-enhancing” environment. We found that, in isolated preparations, swim episode duration and swim burst frequency are greatly increased when the supraesophageal ganglion is removed, but the subesophageal ganglion is intact. The prolonged swim durations observed with the anterior-most ganglion removed were abolished by removal of the tail ganglion. Experiments on the nearly intact leeches show that, in these preparations, the subesophageal ganglion acts to decrease cycle period but, unexpectedly, also decreases swim duration. These results suggest that the supraesophageal ganglion is the primary structure that constrains leech swimming; however, the control of swim duration in the leech is complex, especially in the intact animal.

Imaging fictive locomotor patterns in larvalDrosophila

“…In experiments here, both forward and backward waves still occurred when the brain was removed. The occurrence of locomotor patterns after removal of the brain has also been observed in the leech ( Mullins et al 2012 ), caterpillar ( Dominick and Truman 1985 ), locust ( Kien 1983 ), and cockroach ( Ridgel et al 2007 ), among other invertebrate species. However, the degree of dependence on the brain seems to differ between animal groups, as in highly cephalized vertebrates the nervous system appears to rely on the brain for the initiation of locomotor behavior ( Soffe et al 2009 ; Whelan 1996 ).…”

“…The brain and SOG have previously been implicated in affecting the likelihood to produce particular patterns of locomotor behavior in several species ( Dominick and Truman 1985 ; Kien 1983 ; Kien and Altman 1984 ; Mullins et al 2012 ). We have noticed an increase in the frequency of forward waves but decrease in backward waves once the brain was removed ( Fig.…”