SUMMANY1. A number of motor cell bodies have been identified in the segmental ganglia of the ventral nerve cord of the medicinal leech. These motoneurones supply either excitatory or inhibitory innervation to the muscles in the body wall.2. Several tests were made to establish that each of the identified motoneurones directly innervates muscle fibres. (a) By injecting a fluorescent dye into the cell bodies of motoneurones, their axons were traced through one or both contralateral roots. (b) Electrical stimulation of a motoneurone by an intracellular electrode caused a single nerve impulse to travel through the roots to the muscles where it set up an excitatory or an inhibitory junctional potential. (c) Impulses set up in the roots were conducted antidromically to the cell body. (d) If the preparation was bathed in 20 mM-Mg2+, which blocks chemical synapses, conduction from the cell body to the muscles was not interrupted. Thus it is unlikely that an interneurone was interposed in the pathway within the ganglion.3. Fourteen pairs of excitatory cells and three pairs of inhibitory cells can be identified in each of the twenty-one segmental ganglia. These neurones together supply the five different muscle layers in each segment which execute the movements of the leech. Each neurone innervates a territory of muscle fibres which has a consistent size and location from segment to segment. Several lines of evidence suggest that the identified cells form a major fraction of the total number of excitatory motoneurones in the ganglion.4. The territories of the motoneurones are arranged in a quilt-like pattern closely resembling that already found for the receptive fields of sensory cells on the skin. Within the longitudinal muscle sheet, individual

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to adapt, centering their operating range on the value of presynaptic voltage set by the background light intensity. Even when the photoreceptor is maintained in a depolarized state in bright lights, these hardy synapses do not fatigue (Hayashi et al., 1985). This intriguing syn-

SUMMARY The SLC6 family comprises proteins that move extracellular neurotransmitters, amino acids and osmolytes across the plasma membrane into the cytosol. In mammals, deletion of SLC6 family members has dramatic physiologic consequences, but in the model organism Drosophila melanogaster, little is known about this family of proteins. Therefore,in this study we carried out an initial analysis of 21 known or putative SLC6 family members from the Drosophila genome. Protein sequences from these genes segregated into either well-defined subfamilies, including the novel insect amino acid transporter subfamily, or into a group of weakly related sequences not affiliated with a recognized subfamily. Reverse transcription-polymerase chain reaction analysis and in situhybridization showed that seven of these genes are expressed in the CNS. In situ hybridization revealed that two previously cloned SLC6 members, the serotonin and dopamine transporters, were localized to presumptive presynaptic neurons that previously immunolabelled for these transmitters. RNA for CG1732 (the putative GABA transporter) and CG15088 (a member of the novel insect amino acid transporter family)was localized in cells likely to be subtypes of glia, while RNA for CG5226, CG10804 (both members of the orphan neurotransmitter transporter subfamily) and CG5549 (a putative glycine transporter)were expressed broadly throughout the cellular cortex of the CNS. Eight of the 21 sequences were localized outside the CNS in the alimentary canal,Malpighian tubules and reproductive organs. Localization for six sequences was not found or not attempted in the adult fly. We used the Drosophilaortholog of the mammalian vesicular monoamine transporter 2, CG33528,to independently identify monoaminergic neurons in the adult fly. RNA for CG33528 was detected in a limited number of cells in the central brain and in a beaded stripe at the base of the photoreceptors in the position of glia, but not in the photoreceptors themselves. The SLC6 localization observations in conjunction with likely substrates based on phylogenetic inferences are a first step in defining the role of Na/Cl-dependent transporters in Drosophila physiology.

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