Akiyoshi Niida

Visual responses of morphologically identified tectal neurons in the crucian carp

Tectal neurons of the crucian carp were functionally and morphologically identified by recording their electrical activity and simultaneously injecting dye (Procion yellow). Among intrinsic tectal neurons, visual neurons successfully stained with dye were pyramidal, pyriform and uncategorized neurons. The stained intrinsic tectal neurons were classified into 4 types, according to their visual response properties, i.e. sustained, dimming, transient and other response types. In 23 stained neurons we studied, no correlation was established between response properties and morphology of tectal neurons. In stained pyramidal neurons, the following receptive field (RF) organization could be recognized: (1) on-center, off-surround; off-center, on-surround; both with a small RF; and (2) excitatory or inhibitory center only, with a large RF.

Efferent tectal cells of crucian carp: physiology and morphology.

Tectal cells of the crucian carp (Carassius ararssius) showing antidromic responses evoked by rhombencephalic electrical stimulation were physiologically studied and subsequently stained with Lucifer Yellow CH. The stained efferent tectal cells were fusiform, horizontal, and multipolar. The main axon of these efferent tectal cells descended along the wall of the deep tegmentum and could be traced to the motor area below the cerebellum. The axons gave off their collaterals in several brain areas: 1) descending collaterals in the torus semicircularis, dorso-lateral tegmental area and mesencephalic reticular formation and 2) an ascending collateral in the area between the hypothalamus and tegmentum. Fifty percent of the efferent cells were unresponsive to visual stimuli, but some of these cells were activated by visual or tactile stimulation in conjunction with rhombencephalic electrical stimulation. On the other hand, most of the visually active cells were On-transient and movement sensitive with habituation and some were bimodal.

An extensive projection of fish dorsolateral tegmental cells to the optic tectum revealed by intra-axonal dye marking

The cells of the dorsolateral tegmental (DLT) nucleus in the crucian carp (Carassius carassius) were physiologically identified and marked with Lucifer dye. All the identified DLT cells receive both visual and rhombencephalic inputs. These cells project their axons into the contralateral tectum via the tectal commissure as well as into the ipsilateral tectum. The most striking characteristic of the DLT cells was the wide distribution of their axonal branching in the ipsilateral tectum.

Peripheral targets of centrally located putative accessory neurons of MRO in the isopod Ligia exotica.

SUMMARY The three centrally located putative accessory neurons of the muscle receptor organ (MRO) of the isopod Ligia exotica were identified to the third segmental nerve (N3) of the thoracic ganglion by backfilling with Lucifer Yellow. These neurons were then studied intracellularly and extracellularly to determine whether they suppressed the stretch-activated responses of thoracic stretch receptors. Intracellular injection of depolarizing currents into these three putative accessory neurons revealed that only neuron #3 had an inhibitory effect, suggesting that it is an inhibitory accessory neuron related to thoracic stretch receptors. We searched for the peripheral targets of neurons #1 and #2 by intracellular filling with Lucifer Yellow or by recording of junctional potentials in extensor muscles, and show that they are motor neurons that innervate the deep extensor and superficial extensor muscles, respectively.

Morphological and physiological development of anterior thoracic stretch receptors in two isopods, Armadillidium vulgare and Ligia exotica

Abdominal muscle receptor organs (MROs) monitor the position and movement of abdomen in crustaceans. Thoracic segments of decapods are fused and immovable. It is speculated that MROs had retrograded simple shape, N-cells that lost receptor muscles, a receptor cell and accessory nerves. We focused on the effect of segmental movement in respect to thoracic N-cells and MROs in isopods that have movable thoracic segments. Armadillidium vulgare rolled up its body segments. Ligia exotica swam by quick movement of the posterior thoracic segments. Both isopods possessed N-cells and MROs in the thorax. N-cells were a simple structure, but N-cells from the second and third thoracic segments of A. vulgare had a muscle strand. MROsT3–T4 (from the third and fourth thoracic segments) of A. vulgare had two receptor muscles. MROsT3–T4 of L. exotica had one long receptor muscle. N-cells of both species and MROs of A. vulgare showed slowly adapting stretch-activated discharges. MROs of L. exotica showed both slowly and rapidly adapting discharges. The stretch-activated responses of N-cells and MROs inhibited each other. N-cells or MROs in the thorax of isopods are not related to the segmental structure. The morphology and physiology of N-cells and MROs are specialized to species–specific behaviors.