Evidence of an x zone in lobule V of the squirrel monkey (Saimiri sciureus) cerebellum: The distribution of corticonuclear fibers

Summary The distribution of corticonuclear fibers to medial-most parts of the posterior interposed nucleus (NIP) from lateral areas of the vermis was studied in the squirrel monkey (Saimiri sciureus), using a silver impregnation method. The origin and course of degenerated fibers were studied in serial sections. The distribution pattern of corticonuclear fibers from a series of small well localized lesions placed in the vermis and paravermal cortex of lobule V is compatible with the interpretation that an x zone is present inSaimiri. A comparison of the positions of lesions and the trajectory of fibers arising therein suggests that corticonuclear input to medial-most parts of the NIP originated from a narrow cortical area (about 0.5–0.7 mm wide) located between a cortical area projecting into the medial cerebellar nucleus (the A zone) and a laterally adjacent area (the B zone) which related to the lateral vestibular nucleus. This NIP-projecting cortical area, located about 1.7 mm to 2.5 mm off the midline in lobule V, is interpreted as the x zone in this primate; it extends from lobule IV into lobule VI in squirrel monkey. Corticonuclear fibers of zone x in this primate form a comparatively small terminal field in the medial-most portions of NIP. This contrasts with the distribution of corticonuclear fibers of the C₂ zone which consistently distribute to terminal fields that are shifted into more central areas of NIP. There appears to be no overlap of the corticonuclear terminal fields in the NIP for zone x versus the C₂ zone. These results were correlated with data from the literature on the distribution of olivocerebellar fibers to the x zone and the C₂ zone and the arrangement of cerebellar nucleoolivary projections into the inferior olive from the NIP. The x zone and the C₂ zone both receive input from the contralateral medial accessory olive (MAO), both zones project into the NIP, and the NIP projects into those regions of the MAO which, in turn, project to these respective cortical zonesand into the NIP. This suggest that the x zone is a component of the NIP-MAO circuit. Furthermore the proposed function of the x zone would support the view that this sagittal strip may have a more extensive rostrocaudal distribution in primates as compared to the cat.This paper is dedicated to Professor Fred Walberg on the occasion of his 70th birthday.     

Vocalization in the squirrel monkey (Saimiri sciureus) elicited by brain stimulation

Summary In this study 90 electrode positions, obtained from 13 adult squirrel monkeys, are presented from which vocalizations were reproducibly evoked by electrical brain stimulation. For 49 of these positions the evoked vocalization was classified according to our call catalog. Eleven of the 26 vocalizations listed in our catalog were elicitable by electrical brain stimulation. In addition to vocalization of a single type, vocalization sequences, which were indistinguishable from spontaneously occurring ones, could be elicited from fixed electrode positions. Aggression calls were found predominately in the hypothalamus and amygdala, contact calls in the septum. Among the evoked responses occurring simultaneously with vocalization, the genital response is of greatest interest since it also occurs in a spontaneous context with vocalization; specifically as a component of genital display.We are indebted to Miss Garland Talmage for aiding in the evaluation of the histologioal preparations.     

Histochemical studies on the spinal cord of squirrel monkey (Saimiri sciureus)

Summary Detailed histochemical observations have been made on the various components of the spinal cord. The gray matter showed much greater enzymatic activity than the white matter. The neuropil and substantia gelatinosa showed mild G6PD, AChE and BChE activity; moderate SDH, LDH, SE and AC activity; and strong AP, ATPase, and AMPase activity. The pia-arachnoid showed moderate to strong activity of dehydrogenases and phosphatases. The cytoplasm of the neurons and neuronal processes gave moderate to very strong reaction for most of the enzymes except BChE. The areas of synaptic endings show the presence of oxidative enzymes, phosphorylases, ATPase and AMPase. It has been interesting to note that phosphorylases, which have been mostly observed in the cytoplasm, nucleoli and synaptic areas of various neurons and in the neuropil, also show intensely strong reactions in the nuclei of ependymal cells lining the central canal as well as in nuclei of some glial cells.List of Abbreviations used AC Acid phosphatase - AChE Acetyl cholinesterase - AK Alkaline phosphatase - AMPase Adenosine monophosphatase (5 nucleotidase) - AP Amylophosphorylase - ATPase Adenosine triphosphatase - BChE Butyrylcholinesterase - G6PD Glucose-6-phosphate dehydrogenase - LDH Lactic dehydrogenase - MAO Monoamine oxidase - PAS Periodic acid Schiff - SDH Succinic dehydrogenase - SE Simple esterases - UDPG Uridinedephosphoglucose glycogen transferase T.R. Shanthaveerappa in previous publications     

Myelinated granule cell bodies in the cerebellum of the monkey (Saimiri sciureus)

Electronmicrographs of both the vermis and hemisphere of the cerebellum of the squirrel monkey (Saimiri sciureus) show numerous granule cell bodies partially or completely surrounded by myelin. The myelin is of the compact type and consists of 1 to 13 lamellae. In several cases of partially ensheathed cells the myelin is clearly derived from extensions of myelin sheaths that surround small caliber axons. Either all or only the outer lamellae surrounding the axon contribute to the extensions. In the first instance the myelin buckles at its mesaxon pole and the resulting doubled flap extends for a variable distance along the cell surface.     

Visual stimulus control of intracranial self-stimulation in the squirrel monkey (Saimiri sciureus)

Nine squirrel monkeys were successfully trained on a mult CRF extinction program with electrical brain stimulation as the reinforcer. The reinforced stimulus (S^d) was a green cue light; the nonreinforced stimulus (S^Δ) was a white light. Response rates during S^d reflected prior continuous reinforcement (CRF) responding. Only four of the monkeys learned to suppress responses during S^Δ and immediately resume responding with the onset of S^d. The others continued periodically to sample the lever until stimulation was reinstated. The latter is characteristic of animals responding on a mixed schedule without external cues. Discrimination mastery could be predicted from orientation movements observed during prior CRF extinction. Twice the number of such movements were recorded for discriminators. There was no increased resistance to extinction in comparisons between discriminators and nondiscriminators or CRF extinction and discrimination extinction performance. A significant increased resistance to extinction was found for all females when evaluated with the three min pause criterion. Transfer of stimulus control with other electrodes required practice only for those sites in neuroanatomically dissimilar structures; however, positive transfer was always exhibited.     

Distribution of GABA-immunoreactive neurons in the thalamus of the squirrel monkey (Saimiri sciureus)

A light microscopic study of the cellular localization of GABA in the thalamus of the squirrel monkey (Saimiri sciureus) was undertaken by means of the indirect peroxidase-antiperoxidase method using a highly purified antiserum directed against GABA-glutaraldehyde-lysyl-protein conjugate. GABA-immunoreactive cell bodies and axon terminals were visualized in all thalamic nuclei in the squirrel monkey but their relative density varied from one nucleus to the other. At the level of the anterior nuclear group, GABA-positive cells and terminals abounded in the anterodorsal nucleus but were much less numerous in the anteromedial and anteroventral nuclei. In the nuclei of the ventral group, GABA-immunoreactive cells were found to be smaller and less numerous than nonimmunoreactive neurons. In the ventral anterior nucleus, GABA-positive neuronal profiles formed typical clusters, whereas they were more uniformly distributed in the posterior nuclei of the ventral group. In the intralaminar nuclei, GABA-immunoreactive cells and terminals abounded in the dorsal portion of the paracentral and centrolateral nuclei, whereas more caudally, GABA-positive terminals pervaded the entire parafascicular nucleus. In the mediodorsal nucleus, GABA-positive cell bodies and axon terminals formed typical clusters of various sizes scattered within the lateral parvocellular portion of the nucleus, while GABA-immunoreactive neuronal profiles were less numerous and more uniformly distributed in the medial portion of this structure. In the nuclei of the posterior group, GABA-immunoreactive neuronal profiles were uniformly distributed except in the pulvinar where they abounded in the inferior and oral parts but were scarce in the medial part. In the dorsal lateral geniculate nucleus, the magnocellular layers received the most massive GABA-positive innervation and contained the largest number of GABA-immunoreactive cell bodies. In the ventral lateral geniculate nucleus, GABA-positive cells occurred only ventrolaterally while GABA-immunoreactive terminals pervaded the entire structure. In the medial geniculate nucleus, GABA-immunoreactive cell bodies and terminals abounded particularly within the ventromedial third of the structure. In the habenula, a few GABA-immunoreactive cell bodies and numerous GABA-positive terminals were scattered throughout the lateral habenular nucleus, whereas only a few GABA-immunoreactive terminals surrounded the closely packed unreactive cells in the medial habenular nucleus. In contrast to other thalamic nuclei all neurons in the reticular nucleus displayed GABA immunoreactivity.(ABSTRACT TRUNCATED AT 400 WORDS)     

On the A. malaris of the common squirrel monkey (Saimiri sciureus)

Detailed observations were made of the a. malaris in 11 adult common squirrel monkeys (Saimiri sciureus) utilizing the plastic injection method. The malar artery was well-developed in all 21 examples observed and arose medially from the infraorbital artery proximal to the entrance of the infraorbital canal and lateral to the obliquus inferior muscle. The a. malaris passed superomedially outside the periorbita on the orbital surface of the maxilla and curved medially in front of the muscle, where it gave rise to the infraorbital nerve, the periosteal, the inferior oblique muscular and the infraorbital marginal branches. However, these branches arose directly from the infraorbital artery in many cases. The malar artery ascended in the lower eyelid up to the bottom of the lacrimal sac, where it gave rise to the third palpebral branch and the medial inferior palpebral artery. This artery did not anastomose with peripheral branches of the supraorbital artery. The malar artery continued to pass superomedially behind the lacrimal sac and gave off the nasolacrimal canal and the lacrimal sac branches. However, the former arose in common with the latter in many cases. The malar artery finally ascended behind the medial palpebral ligament after giving off the dorsal nasal branch and the medial superior palpebral artery at the superior end of the lacrimal sac. Its main stream formed a strong communication with the dorsal nasal artery of the supraorbital artery. This communication in an arc was characteristic in the common squirrel monkey. The medial inferior and superior palpebral arteries were well-developed in all examples and formed distinct, inferior and superior palpebral arterial arches by anastomosing with the lateral fellows of the lacrimal, respectively. A large arterial ring surrounding the upper tarsus was constructed from the superior palpebral arterial arch, branches of the lateral superior palpebral artery and the palpebral branch of the supraorbital artery.     

Differential connections of caudate nucleus and putamen in the squirrel monkey (Saimiri sciureus)

The organization of the subcortical connections of caudate nucleus and putamen in the squirrel monkey was studied using horseradish peroxidase conjugated to wheat germ agglutinin as anterograde and retrograde neuronal tracer. The tracer was injected in similar quantities in the putamen on the left side and in the caudate nucleus on the right side in 10 monkeys, and its presence was revealed by means of the tetramethylbenzidine method. The study of anterogradely labeled fibers visualized after such injections shows that putaminofugal fibers terminate massively in the ventral two-thirds of the globus pallidus, where they display a band-like arrangement, and much less abundantly in the caudal third of the substantia nigra. In contrast, caudatofugal fibers occupy only the dorsal third of globus pallidus but arborize profusely in the rostral two-thirds of substantia nigra. In the pars reticulata of the substantia nigra the caudatonigral fibers form a highly complex network composed of fiber trabeculae while the putaminonigral fibers occur as more discrete fascicles confined to the dorsolateral region of the structure. In the pars compacta of the substantia nigra the retrogradely labeled cells occur in the form of clusters that are closely intermingled with clusters of unlabeled neurons. The labeled-cell clusters are particularly dense on the putamen-injected side and more loosely organized on the caudate-injected side. On both sides, however, the striatonigral fibers that reach the substantia nigra pars compacta can be seen to terminate almost exclusively upon clusters composed of retrogradely labeled cells, suggesting the existence of a precise reciprocal link between nigral and striatal neuronal aggregates. At thalamic levels the retrogradely labeled cells are distributed according to a strikingly asymmetric pattern. For instance, a prominent labeling of neurons in the central superior lateral nucleus is seen only on the caudate-injected side. Furthermore, in the centromedian/parafascicular complex retrograde cell labeling is seen exclusively in parafascicular nucleus on the caudate-injected side and only in the centromedian nucleus, except its lateralmost portion, on the putamen-injected side. Control experiments involving injection of the tracer in cerebral cortex overlying the striatum reveal that the neurons in the lateral segment of the centromedian, which do not project to striatum, are in fact reciprocally connected with the cerebral cortex. In addition, our data show that some of the so-called "specific" thalamic nuclei contribute significantly to the thalamostriatal projection in monkey.(ABSTRACT TRUNCATED AT 400 WORDS)     

Ultrastructure of merkel cells in the hard palate of the squirrel monkey (Saimiri sciureus)

The distribution and ultrastructure of Merkel cells in the hard palate was investigated in the squirrel monkey (Saimiri sciureus) after fixation by vascular perfusion. Merkel cells were clustered at the base of the epithelial rete pegs of the hard palate. They were characterized by concentrations of dense-cored granules and closely associated intraepithelial nerve endings. Numerous spiny processes extending from the Merkel cell were intercalated with adjacent keratinocytes, probably serving to detect and amplify movement of adjacent cells. These spiny processes contained a rigid core of parallel microfilaments which were interrelated with cytoplasmic filament bundles located beneath the cell membrane. Transitional cells containing dense-cored granules and well developed tonofibrils appear to be related to both Merkel cells and keratinocytes. The findings of this study suggest that Merkel cells are highly adapted for detection of movement in adjacent keratinocytes, as well as movement of the epithelium with respect to the underlying connective tissue.     

Myelinated granule cell bodies in the cerebellum of the monkey (Saimiri sciureus).

Electronmicrographs of both the vermis and hemisphere of the cerebellum of the squirrel monkey (Saimiri sciureus) show numerous granule cell bodies partially or completely surrounded by myelin. The myelin is of the compact type and consists of 1 to 13 lamellae. In several cases of partially ensheathed cells the myelin is clearly derived from extensions of myelin sheaths that surround small caliber axons. Either all or only the outer lamellae surrounding the axon contribute to the extensions. In the first instance the myelin buckles at its mesaxon pole and the resulting doubled flap extends for a variable distance along the cell surface.     

Circadian control of thermoregulation in the squirrel monkey, Saimiri sciureus.

The characteristics and control of the circadian rhythms of core body temperature (colonic) and skin temperature (tail) were studied in chair-acclimatized squirrel monkeys (Saimiri sciureus). When animals were entrained to a light-dark cycle (12 h 600 lx; 12 h less than 1 lx) these two temperatures displayed prominent, reproducible, tightly coupled circadian rhythms. In contsant light of 600 lx, where no other effective circadian time cues were present, both temperature rhythms persisted with free-running periods. Within each animal, however, these rhythms were not as tightly coupled to one another as in LD. On occasion colonic and tail temperature rhythms free-ran with different circadian periods and some animals demonstrated "splitting" of the colonic temperature rhythm, with the colonic temperature rhythm displaying a bimodal pattern. These results suggest that the circadian rhythm of body temperature in primates is under the control of more than one potentially independent circadian oscillator.     

Vocal repertoire of the squirrel monkey (Saimiri sciureus), its analysis and significance

Summary Two hundred and fifty vocalizations of the squirrel monkey (Saimiri sciureus) were selected for spectrographic analysis from a total of 200 hrs. of tape recordings. The vocalizations were classified into six groups according to their physical characteristics. Both intra and intergroup variability of calls was observed. Calls of similar shape were found to have similar functions. Thus each group of calls could be characterized by a functional designation. The functional significance of calls was determined by qualitative and quantitative observations. Four methods were employed: 1. stereotyped vocalizations were elicited by visual stimuli; 2. motor and vocal reactions were evoked through adequate vocal signals; 3. vocalizations were observed when external conditions were held constant and internal factors were permitted to vary; 4. vocal events were related to the total social situation. By these methods the complexity as well as the specificity of the vocal communication system is demonstrated and its evolutionary significance is discussed.     

Microvascular architecture of the palatine mucosa in the common squirrel monkey (Saimiri sciureus).

Detailed observations were made of the structure and microvasculature of the palatine mucous membrane of the common squirrel monkey (Saimiri sciureus) by means of the plastic injection method under a scanning electron microscope. The findings obtained were compared with those of the Japanese monkey and other mammals. The osseous palate was flat horizontally and a pair of incisive foramina were apparently open at the anterior end of the hard palate. At the posterior end of the osseous palate, the pterygopalatine incisurae were found bilaterally. The incisive papilla was not obvious in form and size, and a pair of openings of the incisive canal were always situated on both sides of the papilla. The transverse palatine plicae or ridges numbered 7 or 8 symmetrically. They arched posterolaterally with an anterior protrusion near each median end. Posterior plicae were underdeveloped. Numerous openings of the palatine glands were found in the soft palatine mucosa. The arteries supplying the palate were the major palatine artery passing through the major palatine foramen and the soft palatine artery passing through the pterygopalatine incisura. The major palatine artery extended forwards giving off numerous medial and lateral branches, and its end on the respective side entered a small foramen located lateral to the incisive foramen. Medial and lateral branches formed the submucous arterial network. Arterioles diverging from this network were directed to the epithelial surface and formed an arterial network in the lamina propria. Further, capillaries diverging from the latter network built up the subepithelial capillary network immediately beneath the epithelium. Capillary loops sprouting from the capillary network were found in the form of a simple hair-pin without locational differences in their heights. The microvascular architecture thus displayed some similarity with that of the Japanese monkey. However, the vascular networks in the lamina propria and submucous layer were not distinct in size and scale as compared to those of the Japanese monkey. These differences may be related to the stature, living environment and food habits of this species.