Glutamate as a transmitter in the sensory pathway from prostomial lip to serotonergic Retzius neurons in the medicinal leech Hirudo

Changes in the nitric oxide system in the shore crab Hemigrapsus sanguineus (Crustacea, decapoda) CNS induced by a nociceptive stimulus

Using NADPH-diaphorase (NADPH-d) histochemistry, inducible nitric oxide synthase (iNOS)-immunohistochemistry and immunoblotting, we characterized the nitric oxide (NO)-producing neurons in the brain and thoracic ganglion of a shore crab subjected to a nociceptive chemical stimulus. Formalin injection into the cheliped evoked specific nociceptive behavior and neurochemical responses in the brain and thoracic ganglion of experimental animals. Within 5–10 min of injury, the NADPH-d activity increased mainly in the neuropils of the olfactory lobes and the lateral antenna I neuropil on the side of injury. Later, the noxious-induced expression of NADPH-d and iNOS was detected in neurons of the brain, as well as in segmental motoneurons and interneurons of the thoracic ganglion. Western blotting analysis showed that an iNOS antiserum recognized a band at 120 kDa, in agreement with the expected molecular mass of the protein. The increase in nitrergic activity induced by nociceptive stimulation suggests that the NO signaling system may modulate nociceptive behavior in crabs.

Evidence that the swim afferent neurons of tritonia diomedea are glutamatergic

The escape swim response of the marine mollusc Tritonia diomedea is a well-established model system for studies of the neural basis of behavior. Although the swim neural network is reasonably well understood, little is known about the transmitters used by its constituent neurons. In the present study, we provide immunocytochemical and electrophysiological evidence that the S-cells, the afferent neurons that detect aversive skin stimuli and in turn trigger Tritonia's escape swim response, use glutamate as their transmitter. First, immunolabeling revealed that S-cell somata contain elevated levels of glutamate compared to most other neurons in the Tritonia brain, consistent with findings from glutamatergic neurons in many species. Second, pressure-applied puffs of glutamate produced the same excitatory response in the target neurons of the S-cells as the naturally released S-cell transmitter itself. Third, the glutamate receptor antagonist CNQX completely blocked S-cell synaptic connections. These findings support glutamate as a transmitter used by the S-cells, and will facilitate studies using this model system to explore a variety of issues related to the neural basis of behavior.

Molecular identification and expression of the NMDA receptor NR1 subunit in the leech

The N-methyl-D-aspartate receptor (NMDAR) is involved in a number of physiological and pathophysiological processes in vertebrates, but there have been few studies examining the role of invertebrate NMDA receptors. In the leech, pharmacological evidence suggests that NMDARs contribute to synaptic plasticity, but there has been no molecular identification of NMDA receptors. In this report, a partial cDNA encoding the leech NR1 subunit of the NMDA receptor (HirNR1) is presented. Reverse transcriptase-polymerase chain reaction from single neurons of the leech central nervous system confirms HirNR1 expression in the Retzius (R), Anterior Pagoda (AP), Pressure (P), and Touch (T) neurons. Immunoblotting with an anti-NR1 antibody yielded a approximately 110 kDa protein, similar to the expected weight of the NR1 subunit (approximately 116 kDa). Finally, pairing pre- and postsynaptic activity elicited long-term potentiation in synapses between neurons expressing NR1 mRNA (P-to-AP synapse) and this potentiation was blocked by the NMDAR antagonist AP5.