Figure 7. Diverging sensory and interneuronal paths converge onto a linked set of output neurons.

Circuit architecture common for all RPNs (CRZ single-cell example). 1: the strongest polysynaptic path based on hub analysis from pharyngeal sensory origin to CRZ output neuron via interneuron 10. 2: second interneuron (12) integrating enteric information and different pharyngeal information, converging onto CRZ output neuron. 3: all interneurons of one CRZ output neuron integrating multiple sensory origins and converging onto one single output. 4: concept of divergence and convergence in the neuroendocrine connectome. Sensory neurons diverge/converge onto distinct sets of interneurons. Interneurons diverge in varying synaptic strength onto distinct sets of linked RPN output neurons. Numbers at bottom show degree of convergence and divergence (e.g., interneuron 10 diverges to CRZ, ITP, PTTH, and CA-LP; all interneurons converge to CRZ; synaptic threshold = 3 for all connections). CA-LP: corpus allatum innervating neurosecretory neurons of the lateral protocerebrum; CO₂: carbon dioxide; CRZ: corazonin neurons; DH44: diuretic hormone 44 neurons; DMS: Drosophila myosuppressin neurons; ens: enteric nervous system; IPCs: insulin-producing cells; ITP: ion transport peptide neurons; ph: pharynx; PTTH: prothoracicotropic hormone neurons; som: somatic; RPNs: ring gland projection neurons.

Figure 7—figure supplement 1. Diverging single-cell RPN circuits.

Shown are, based on single-output RPN cell, circuits from sensory origins (single cells) via interneurons (single cells) to output (single cell). Included are also interneurons (upstream of one particular RPN), which do not receive input from sensory neurons (pink interneurons). These are shown on the left panel for each RPN set. Converging paths onto a specific output RPN automatically result in connections to different sets of RPNs (‘linked RPNs’). These linked RPN paths are shown on the right panel for each RPN set. Using DMS 1L as an illustration, a series of parallel paths from different sensory neurons converge, either directly or via a layer of interneurons (presented vertically), onto a single-output cell. In addition, there is another layer of interneurons, but that have no direct contact to sensory neurons (presented horizontally), that also converge onto the same output cell. These pathways are then found to converge, in varying strengths, onto additional RPNs (in this case, a total of six cells), thus forming a linked set of outputs. The same principle applies to RPNs with no direct sensory connections, such as CRZ. For abbreviations, see Figure 6—figure supplement 2.