Synaptic connections between pigment‐dispersing factor‐immunoreactive neurons and neurons in the pars lateralis of the blow fly Protophormia terraenovae

Sep 22, 2005The Journal of comparative neurology

Connections between pigment-dispersing factor neurons and thinking areas in the blow fly Protophormia terraenovae

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Abstract

PL neurons in the blow fly Protophormia terraenovae are essential for reproductive diapause under specific environmental conditions.

Neurons in the pars lateralis project to the retrocerebral complex and are necessary for diapause induction.
Immunolight microscopy revealed overlap between PL neuron fibers and those containing pigment-dispersing factor (PDF).
Immunoelectron microscopy showed output synapses formed between PDF-immunoreactive fibers and PL neurons.
Synaptic connections between PDF fibers and PL neurons were sparse in the examined regions.
PDF-immunoreactive fibers likely originate from neurons in the medulla of the optic lobe, associated with circadian rhythms.

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In females of the blow fly Protophormia terraenovae, neurons with cell bodies in the pars lateralis (PL) projecting to the retrocerebral complex (designated as PL neurons) are necessary for the induction of reproductive diapause under short-day and low-temperature conditions. In the present study, neural connections between PL neurons and pigment-dispersing factor (PDF)-immunoreactive neurons were examined via immunolight microscopy and immunoelectron microscopy combined with backfills through the cardiac-recurrent nerve. Immunolight microscopy showed that fibers of PL neurons overlapped with PDF-immunoreactive fibers in the dorsolateral region of the superior protocerebral neuropil. Immunoelectron microscopy showed that PDF-immunoreactive fibers formed output synapses with fibers of PL neurons and unlabeled neurons in a region dorsoanteriorly located with respect to the calyx of the mushroom body. The distribution of synaptic connections between PDF-immunoreactive fibers and the fibers of PL neurons was sparse. According to the projection patterns, PDF-immunoreactive fibers with synaptic connections with PL neurons appeared to originate from PDF-immunoreactive neurons with cell bodies at the base of the medulla of the optic lobe (medulla PDF neurons), which are putative circadian clock neurons in P. terraenovae. PDF immunoreactivity was restrictively detected in dense-core vesicles but not in clear synaptic vesicles. The present results suggest that medulla PDF neurons convey time or photoperiodic information to PL neurons for diapause induction through direct synaptic connections.

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Synaptic connections between pigment‐dispersing factor‐immunoreactive neurons and neurons in the pars lateralis of the blow fly Protophormia terraenovae

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