Tomio Arikuni

Fine-structural study of the pineal body of the monkey (Macaca fuscata) with special reference to synaptic formations.

SummaryVarious types of synaptic formations on pinealocytes and pineal neurons were found in the pineal body of Macaca fuscata. Axo-somatic synapses of the Gray type-II category were detected on the pinealocyte cell body. Gap junctions and ribbon synapses were observed between adjacent pinealocytes. About 70 nerve-cell bodies were detected in one half of the whole pineal body bisected midsagittally. They were localized exclusively deep in the central part. When examined electron-microscopically, they were found to receive ribbon-synapse-like contacts from pinealocytic processes. They also received synaptic contacts of the Gray type-I category on their dendrites, and those of the Gray type-II category on their cell bodies from nerve terminals of unknown origin. All these synapse-forming axon terminals contained small clear vesicles. Thus, the pineal neurons of the monkey, at least in part, are suggested to be derived from the pineal ganglion cells in the lower vertebrates and not from the postganglionic parasympathetic neurons. The functional significance of these observations is discussed in relation to the innervation of the pineal body of the monkey.

Claustral and amygdaloid afferents to the head of the caudate nucleus in macaque monkeys.

A single dose of horseradish peroxidase polyacrylamide gel (10%, 1.0 microliter) was injected, after callosotomy, into the head of the caudate nucleus in six macaque monkeys. In addition to the previously reported structures sending fibers to the caudate nucleus, such as the cerebral cortex, substantia innominata, thalamus, hypothalamus, substantia nigra and brainstem, labeled cells were found abundantly in the rostral portion of the ipsilateral claustrum, and fewer labeled cells were dispersed in the ipsilateral external and extreme capsules. Many labeled cells were also present in the ipsilateral insular cortex throughout its rostrocaudal extent. Moreover, labeled cells were seen ipsilaterally in the basolateral, basomedial, accessory basal, and cortical nuclei of the amygdaloid complex.

Topographical projections from the prefrontal cortex to the post-arcuate area in the rhesus monkey, studied by retrograde axonal transport of horseradish peroxidase

The cells of origin of ipsilateral, prefrontal cortical projections to the post-arcuate area were studied in rhesus monkeys with the horseradish peroxidase (HRP) method. Following injections of HRP into the dorsal portion of the post-arcuate area, retrogradely labeled cells appeared in the arcuate area dorsal to the principal sulcus, while, following injections into its ventral portion, labeled cells appeared in the arcuate area ventral to the principal sulcus. They were pyramidal cells and lay mainly in the III layer, but small numbers of them were also found in the IV and V layers. In addition, HRP labeled cells were seen ipsilaterally in the banks of the cingulate sulcus.

Substantia innominata projection to caudate nucleus in macaque monkeys

The distribution of the cells of origin projecting from the substantia innominata to the caudate nucleus was studied in macaque monkeys by means of the retrograde axonal transport of horseradish peroxidase (HRP). The HRP was injected, after callosotomy, into the exposed head of the caudate nucleus. Labeled cells appeared in the ipsilateral substantia innominata, extending rostrally to the level of the optic chiasma.

Inhibitory potentials produced in cortical cells by stimulation of the lateral hypothalamus in rabbits

(1) Intracellular potentials were recorded from pyramidal tract (PT) and non-pyramidal tract (non-PT) cells of the frontal cortex in urethane-anesthetized rabbits and the effects of electrical stimulation of the lateral hypothalamus (LH) were examined on the ipsilateral side. (2) Latencies of antidromic spikes of PT cells evoked by stimulation of the medullary pyramidal tract (PYR) had a unimodal distribution with the mean at 4.0 msec. The mean conduction velocity of the pyramidal tract fibers was 10.5 m/sec. (3) Prolonged IPSPs were produced in PT and non-PT cells by single shock stimulation of LH (LH-IPSP). They were significantly longer lasting than those produced by PYR stimulation (PYR-IPSP). (4) The latencies of LH-IPSPs ranged from 1.7 to 25.0 msec and were divided into two groups. The latencies of PYR-IPSPs had a unimodal distribution ranging from 2.5 to 30 msec. (5) In a few non-PT cells, a sequence of brief depolarization and prolonged hyperpolarization occurred in response to LH stimulation. (6) In some non-PT cells, EPSPs which occasionally resulted in spike discharges were observed after LH stimulation. However, no excitation of PT cells was observed by LH stimulation.

Topographical organization of the afferent connections of area 24 from the insular and temporal cortices in the macaque monkey

The presubiculum (PreS) plays a role of the interface between the medial entorhinal cortex (MEA) and the anterior thalamic nuclei as well as the subiculum. We reported that the layer III cells of PreS projected to MEA, while the layer II cells concerned with the associational connection in PreS. In this study, further analysis was made using the WGA-HRP and PHA-L method. The association cells were widely distributed in the PreS including area 29e, and the majority were in the temporal half. The cells in the septal PreS projected far to the temporal PreS, while the cells in the temporal PreS terminated mostly within the temporal portion. Transversely, the association cells were located densely in the mid and distal parts (far from the subiculum), but very few in the proximal part. As to the reciprocal connection between the MEA and layer III of PreS, the following topography was observed: 1) the septal PreS was connected with the lateral MEA, and the temporal PreS with the medial MEA, and 2) the distal PreS connected with the septal MEA and the proximal PreS with the temporal MEA.