Retinal central projection in developing xenopus tadpoles

$27

6 Development I Anatomy RETINAL

CENTRAL

}~JIME

FUJISAWA,

Department

of Anatomy,

Kamikyo-ku,

Kyoto

By labeling pathways traced, 50.

PROJECTION

axons

of r e t i n a l

The

following axons

rectum,

pretectal which

passing

through

optic

with

toward

correct

their

that

of r e t i n a l

axons

via

probably and

nucleus

the c e n t r a l

Each

subset

centers,

anomalous

retinal

by direct

s u c h as

routes.

the

the

or basal

the optic axons,

arrived These

optic

between

after tract

or

there

at

their

findings

can recognize

contact

of

or diencephalon,

that had

axons

at s t a g e

s u c h as

those normally-routed axons

were

tadpoles

of Belonci,

routes,

retinal

individual

centers,

obtained.

in the m i d b r a i n

Besides

centers

of M e d i c i n e ,

centers

of X e n o p u s

own visual

specific

mis-routed

visual

indicate

were

their

formed

their visual

brains

neuropile,

were

TADPOLES

University

horseradishperoxidase,

results

route.

several

visual

Prefectural

XENOPUS

Japan.

axons

reached

nucleus

basal

Kyoto

in the whole-mounted

retinal

were

602,

IN DEVELOPING

their

growing

may

own tips

targets.

DENDRITIC GROWTH RATE IN VIVO AS STUDIED IN ZONA INTERHEDIA NEURONS OF THE CHICK E[~RYO WITH THE GOLGI METHOD AKIRA KANEMITSU and SEIJI HATSUDA , Department of Neuroanatomy, School of Hedicine, University of Tokyo, 7-3-1Hongo, Bunkyo-ku, Tokyo 113, Japan. In the upper cervical cord of chick embryos at stages 2 7 , 2 8 and 31, synapses were observed for the most part in the primordial dorsal, lateral and ventral funiculi, suggesting that neurons located deep in the mantle layer extend their dendrites to the funiculus to make synaptic contact in earlier developmental stages. We examined the distribution of dendrites and measured the length from the center of cell soma to the tip of the longest dendrite of each impregnated neuron in the zona intermedia at stages 24, 27, 29, 30, 33, 36, 38, 41 and 45, to know the stage when the neurons located deep in the mantle layer reach the primordial funiculus by their longest dendrite and to obtain the dendritic growth rate in vivo. To obtain data from neurons homogeneous in regard to their time of origin, measuring was done exclusively on large neurons in each stage, because large neurons in the zona intermedia are known to differentiate almost synchronously at the early stage of development. The results are summarized as follows: at stage 27, neurons in the zona intermedia reached by their longest dendrite the primordial dorsal, lateral or ventral funieulus, which was the site of synaptic contact formation in early developmental stages; and the average length of the longest dendrite for each stage was 30, 120, 170, 180, 200, 230, 250, 245 and 290~m, respectively. From these values and the intervals between stages obtained from Hamburger-Hamilton's developmental stage table, the growth rates of the longest dendrite were calculated as 90-180pm per day at stage 54, 45-90~m per day at stage 27, 20~m per day at stages 29, 30 and 33, i0 pm per day at stage 36 and 49m per day after stage 38. It is thus suggested that the initial rapid growth of the dendrites in vivo is highly effective for the early formation of synaptic contacts.