The cingular vocalization pathway in the squirrel monkey

Summary In 39 squirrel monkeys (Saimiri sciureus), the effects of various brain lesions on vocalizations elicited from the precallosal cingulate gyrus were tested. It was found that lesions abolishing the cingular vocalization completely can be traced from the stimulation site continuously down to the laryngeal motoneurons in the nucleus ambiguus. The pathway thus determined (Fig. 4) travels from the precallosal cingulate gyrus through the frontal white matter and enters the internal capsule from a dorsolateral position. The pathway then follows this structure in a medio-caudal direction down to the caudal diencephalon. Here, the effective lesions leave the corticospinal tract and ascend dorsally into the periaqueductal grey. The pathway follows this structure to its end where it sweeps lateral through the parabrachial area and then descends through the lateral pons and ventrolateral medulla to the nucleus ambiguus.In nine of the animals, in addition, the effects of bilateral anterior cingular lesions on vocalizations elicited in other brain areas were tested. It was found that the only vocalization-eliciting area which becomes ineffective after destruction of the anterior cingulate gyrus is the postero-medial orbital cortex.Abbreviations a nucl. accumbens - aa area anterior amygdalae - ab nucl. basalis amygdalae - ac nucl. centralis amygdalae - al nucl. lateralis amygdalae - am nucl. medialis amygdalae - an nucl. anterior thalami - aq griseum centralis - bc brachium conjunctivum - ca caudatum - cb cerebellum - cc corpus callosum - cen nucl. centralis superior Bechterew - ci capsula interna - cin cingulum - cl claustrum - coa commissura anterior - coli colliculus inferior - cols colliculus superior - cop commissura posterior - cr corpus restiforme - csp tractus corticospinalis - db fasciculus diagonalis Brocae - dbc decussatio brachii conjunctivi - f fornix - gc gyrus cinguli - gl geniculatum laterale - gm geniculatum mediale - gp globus pallidus - gr gyrus rectus - gs gyrus subcallosus - h area tegmentalis (Forel) - ha habenula - hi tractus habenulo-interpeduncularis - hip hippocampus - hya hypothalamus anterior - hyv hypothalamus ventromedialis - in nucl. interpeduncularis - lap nucl. lateralis posterior thalami - lem lemniscus medialis - lm fasciculus longitudinalis medialis - m nucl. mammillaris - md nucl. medialis dorsalis thalami - mt tractus mammillothalamicus - nst nucl. striae terminalis - nts nucl. solitarius - oi oliva inferior - ol fasciculus olfactorius (Zuckerkandl) - os oliva superior - p pedunculus cerebri - pmc brachium pontis - po griseum pontis - pro area praeoptica - pu nucl. pulvinaris - put putamen - re formatio reticularis mesencephali - rep nucl. reticularis tegmenti pontis - rl nucl. reticularis lateralis - rub nucl. ruber - s septum - sm stria medullaris - sn substantia nigra - st stria terminalis - sto stria olfactoria lateralis - tec tractus tegmentalis centralis - trz corpus trapezoideum - va nucl. ventralis anterior thalami - ves nucl. vestibularis - vpl nucl. ventralis posterior lateralis th. - vpm nucl. ventralis posterior medialis th. - zi zona incerta - II tractus opticus - IIchde chiasma n. opticorum - III nucl. n. oculomotorii and n. oculomotorius - IV nucl. n. trochlearis - VI n. abducens - VII nucl. n. facialis and n. facialis - VIII n. acusticus - XII nucl. n. hypoglossi     

Vocalization-correlated single-unit activity in the brain stem of the squirrel monkey

Summary The brain stems of 17 squirrel monkeys (Saimiri sciureus) were systematically explored for vocalization-related single-unit activity during calls electrically elicited from the periaqueductal grey. Of 12,280 cells tested, 1151 fired in relation to vocalization. Of these, 587 reacted to external acoustic stimuli and started firing after vocalization onset. As most of these cells were located in classical auditory relay structures, they probably represent auditory neurones reacting indirectly to self-produced vocalization due to auditory feedback. Seven cells reacted to acoustic stimuli but fired in advance of self-produced vocalization. These cells were locoated in the pericentral inferior colliculus, dorsal nucleus of the lateral lemniscus, dorsomedial to the ventral nucleus of the lateral lemniscus and immediately lateral to the central grey. They are probably engaged in tuning the auditory system to process self-generated sounds differently from external sounds. 261 neurones reacted to nonphonatory oral movements (chewing, swallowing) and started firing after vocalization onset. These neurones were widely distributed within the brain stem, with the highest density in the spinal trigeminal nucleus and medially adjacent reticular formation. The majority of these cells seem to react to proprioceptive and tactile stimuli generated by phonatory and nonphonatory oral activities. Some of them may exert motor control on muscles that come into play at later stages of phonation. 57 neurones reacted to nonphonatory oral movements but fired in advance of vocalization onset. These neurones were located mainly in the trigeminal motor nucleus, nucl. ambiguus, reticular formation around these nuclei, parabrachial region and lateral vestibular nucleus. Their role in motor control seems to be related to specific muscles rather than specific functions. 100 of the vocalization-related cells showed a correlation with respiration. Expiration-related cells were found in and around the rostral nucl. ambiguus and in the reticular formation dorsal to the facial nucleus. Inspiration-related cells were located in the rostral and caudal nucl. ambiguus regions, ventrolateral solitary tract nucleus and the lateral reticular formation below the trigeminal motor nucleus. Most of these cells probably represent premotor neurones of respiratory muscles and laryngeal motoneurones of the cricothyroid and posterior cricoarytenoid muscles. Finally, a last group of cells was found that was unresponsive to chewing and swallowing movements, quiet breathing and acoustic stimuli, but changed activity during vocalization. 38 of them became active before vocalization and cricothyroid activity, and 101 afterward. Both types were completely intermingled and scattered widely in the brain stem, including the nucl. ambiguus region, solitary tract nucleus, nucl. reticularis parvocellularis and gigantocellularis, parabrachial region, pericentral colliculus inferior, vestibular complex, periventricular grey and laterally adjacent tegmentum. Some of these cells may be related to vocalization in a more specific way.Abbreviations A nucl. annularis - Ab nucl. ambiguus - Apt area praetectalis - BC brachium conjunctivum - BP brachium pontis - Cb cerebellum - CC corpus callosum - Cd nucl. caudatus - Col colliculus inferior - CoS colliculus superior - CRf corpus restiforme - DBC decussatio brachii conjunctivi - DG nucl. dorsalis tegmenti (Gudden) - DR nucl. dorsalis raphae - DV nucl. ventralis n. vagi - FRM formatio reticularis myelencephali - FRP formatio reticularis pontis - FRTM formatio reticularis mesencephali - GC substantia grisea centralis - GL corpus geniculatum laterale - GM corpus geniculatum mediale - GPM griseum periventriculare mesencephali - GPo griseum pontis - H habenula - Hip hippocampus - IP nucl. interpeduncularis - LC locus coeruleus - LL lemniscus lateralis - LLd nucl. dorsalis lemnisci lateralis - LLv nucl. ventralis lemnisci lateralis - LM lemniscus medialis - LP nucl. lateralis posterior thalami - MD nucl. medialis dorsalis thalami - MV nucl. motorius n. trigemini - NC nucl. cochlearis - NCb nucl. cerebelli - NCS nucl. centralis superior - NCT nucl. trapezoidalis - NR nucl. ruber - NST nucl. supratrochlearis - NSV nucl. spinalis n. trigemini - NTS nucl. tractus solitarii - NIII nucl. oculomotorius - NIV nucl. trochlearis - nV nervus trigeminus - NVI nucl. abducens - NVII nucl. facialis - NXII nucl. hypoglossus - OI oliva inferior - PbL nucl. parabrachialis lateralis - PbM nucl. parabrachialis medialis - Pp nucl. praepositus - Pu nucl. pulvinaris oralis - PuL nucl. pulvinaris lateralis - PuM nucl. pulvinaris medialis - Py tractus pyramidalis - PV nucl. principalis n. trigemini - RL nucl. reticularis lateralis - RTP nucl. reticularis tegmenti pontis - SN substantia nigra - ST stria terminalis - Ves nucl. vestibulares - VR nucl. ventralis raphae - IV decussatio n. trochlearis Supported by Deutsche Forschungsgemeinchaft grant Ju 181/1     

Projections from the cortical larynx area in the squirrel monkey

Summary The projections from the cortical vocal fold area were studied in five squirrel monkeys (Saimiri sciureus) with the aid of the autoradiographie tracing technique. The location of the cortical vocal fold area was determined by exploring the exposed frontal cortex with roving electrodes while examining the larynx for vocal fold adduction. The following projections were found: To the orbital cortex (area 11), dorsomedial frontal cortex (areas 6 and 8), Broca's area (area 44), lower fronto-parietal cortex (areas 6, 4, 3 and 1), fronto-parietal operculum (area 50), insula (areas 14 and 13), caudatum, putamen, claustrum nucl. reticularis th., nucl. ventralis anterior, nucl. ventralis lateralis, nucl. ventralis posteromedialis, nucl. centralis inferior, nucl. centralis lateralis, nucl. medialis dorsalis, nucl. pulvinaris medialis, griseum pontis, nucl. parabrachialis medialis and lateralis, nucl. tr. spinalis n. trigemini and nucl. tr. solitarii.A comparison of this projection system with a previous mapping study for vocalization (Jürgens and Ploog, 1970) revealed that there are two areas yielding vocalization when electrically stimulated which receive direct projections from the cortical larynx area, namely, the cortex around the anterior sulcus cinguli and the parabrachial nuclei at the pons-midbrain transition. The possible relevance of these structures for vocalization is discussed.     

Convergent projections of different limbic vocalization areas in the squirrel monkey

Summary The projections of four different sub-areas within the anterior limbic cortex, all yielding vocalization when electrically stimulated, were compared in six squirrel monkeys by the autoradiographic tracing technique.Areas of convergence of the projections from all four vocalization loci were the cortex within the anterior cingulate sulcus, a zone following the inferior thalamic peduncle from the central amygdaloid nucleus through the substantia innominata into the midline thalamus, a second zone following the periventricular fibre system from the anterior diencephalon to the caudal midbrain and dorsolateral pontine tegmentum and, finally, the tail of the caudate nucleus. Except for the latter, all of these brain structures produce vocalization when electrically stimulated. The call types elicitable from these projection areas are sometimes different from those elicitable from the anterior limbic cortex. It is hypothesized that the anterior limbic cortex controls vocalization directly, independently of the specific motivational state underlying it.Abbreviations to Figures 2 and 3 a nucl. accumbens - aa area anterior amygdalae - ab nucl. basalis accessorius amygdalae - ac nucl. centralis amygdalae - an nucl. anterior thalami - anl ansa lenticularis - aq substantia grisea centralis - ba nucl. basalis amygdalae - bc brachium conjunctivum - ca nucl. caudatus - cc corpus callosum - cent centrum medianum - ci capsula interna - cl claustrum - coa commissura anterior - coi colliculus inferior - csp tractus cortico-spinalis - gc gyrus cinguli - gl corpus geniculatum laterale - gm corpus geniculatum mediale - gp globus pallidus - gpm griseum periventriculare mesencephali - gr gyrus rectus - gts gyrus temporalis superior - h campus Foreli - ha nucl. habenularis - hip hippocampus - hy hypothalamus - lap nucl. lateralis posterior thalami - lem lemniscus medialis - m corpus mamillare - md nucl. medialis dorsalis thalami - os nucl. olivaris superior - p pedunculus cerebri - po griseum pontis - pro area praeoptica - pu nucl. pulvinaris thalami - put putamen - re formatio reticularis - s septum - sm stria medullaris - sn substantia nigra - st stria terminalis - tp cortex temporalis anterior - va nucl. ventralis anterior thalami - vpl nucl. ventralis postero-lateralis th. - vpm nucl. ventralis postero-medialis th. - III N. oculomotorius The study was carried out in accordance with the Guiding Principles in the Care and Use of Primates approved by the Council of the American Physiological Society.     

Brain stimulation-induced changes of phonation in the squirrel monkey

Summary In 11 squirrel monkeys (Saimiri sciureus), the brain stem was systematically explored with electrical brain stimulation for sites affecting the acoustic structure of ongoing vocalization. Vocalization was elicited by electrical stimulation of different brain structures. A severe deterioration of the acoustical structure of vocalization was obtained during stimulation of the caudoventral part of the periaqueductal grey, lateral parabrachial area, corticobulbar tract, nucl. ambiguus and surrounding reticular formation, facial nucleus, hypoglossal nucleus, solitary tract nucleus and along the fibres crossing the midline at the level of the hypoglossal nucleus. It is suggested that these structures are part of, or at least have direct access to, the motor coordination mechanism of phonation. Complete inhibition of phonation was obtained from the raphe and raphe-near reticular formation.Abbreviations Ab nucl ambiguus - APt area praetectalis - BC brachium conjunctivum - BP brachium pontis - Cb cerebellum - CC corpus callosum - Cd nucl. caudatus - Cf nucl. cuneiformis - Cel nucl. centralis lateralis - Cl claustrum - CM centrum medianum - Cn nucl. cuneatus - Co nucl. cochlearis - CoI colliculus inferior - CoS colliculus superior - CP commissura posterior - CPf cortex piriformis - CRf corpus restiforme - CSL nucl. centralis superior lateralis thalami - CT corpus trapezoideum - DBC decussatio brachii conjunctivi - DG nucl. dorsalis tegmenti (Gudden) - DLM decussatio lemnisci medialis - DPy decussatio pyramidum - DR nucl. dorsalis raphae - DV nucl. dorsalis n. vagi - DIV decussatio n. trochlearis - EP epiphysis - FC funiculus cuneatus - FL funiculus lateralis - FLM fasciculus longitudinalis medialis - FRM formatio reticularis myelencephali - FRP formatio reticularis pontis - FRPc formatio reticularis pontis caudalis - FRPo formatio reticularis pontis oralis - FRTM formatio reticularis mesencephali - FV funiculus ventralis - G nucl. gracilis - GC substantia grisea centralis (periaqueductal grey) - GL nucl. geniculatus lateralis - GM nucl. geniculatus medialis - GP globus pallidus - GPM griseum periventriculare mesencephali - GPo griseum pontis - Hip hippocampus - HL nucl. habenularis lateralis - H habenula - IP nucl. interpeduncularis - LC locus coeruleus - LD nucl. lateralis dorsalis thalami - Lim nucl. limitans - LLd nucl. lemnisci lateralis, pars dorsalis - LLv nucl. lemnisci lateralis, pars ventrali - LM lemniscus medialis - LP nucl. lateralis posterior thalami - MD nucl. medialis dorsalis thalami - MV nucl. motorius n. trigemini - NCS nucl. centralis superior - NCT nucl. trapezoidalis - NMV nucl. mesencephalicus n. trigemini - NR nucl. ruber - NSV nucl. spinalisn. trigemini - NTS nucl. tractus solitarii - NIII nucl. oculomotorius - NIV nucl. trochlearis - NVI nucl. abducens - NVII nucl. facialis - NXII nucl. hypoglossus - OI oliva inferior - OS oliva superior - P nucl. posterior thalami - PbL nucl. parabrachialis lateralis - PbM nucl. parabrachialis medialis - PC depedunculus cerebri - Pd nucl. peripeduncularis - Pg nucl. parabigeminalis - Pp nucl. praepositus - PuI nucl. pulvinaris inferior - PuL nucl. pulvinaris lateralis - PuM nucl. pulvinaris medialis - PuO nucl. pulvinaris oralis - Py tractus pyramidalis - Pv nucl. principalis n. trigemini - R Ab nucl. retroambiguus - RL nucl. reticularis lateralis - RTP nucl. reticularis tegmenti pontis - Sf nucl. subfascicularis - SGD substantia grisea dorsalis - SGV substantia grisea ventralis - SN substantia nigra - ST stria terminalis - St subthalamus - TRM tractus retroflexus (Meynert) - TSc tractus spinocerebellaris - Ves nucl. vestibularis - VL nucl. ventralis lateralis - VPI nucl. ventralis posterior inferior - VPL nucl. ventralis posterior lateralis - VPM nucl. ventralis posterior medialis - VR nucl. ventralis raphae - Zi zona incerta - II tractus opticus - VII n. facialis     

Projections of the ventrolateral pontine vocalization area in the squirrel monkey

In four squirrel monkeys (Saimiri sciureus), the tracer biotin dextranamine (BDA) was injected into the ventrolateral pons at a site at which injection of the glutamate antagonist kynurenic acid blocked vocalization electrically elicited from the periaqueductal gray (PAG). Anterograde projections could be traced into all cranial motor and sensory nuclei involved in phonation, that is, the nucleus ambiguus, facial, hypoglossal and trigeminal motor nuclei, the motorneuron column in the ventral gray substance innervating the extrinsic laryngeal muscles, the nucleus retroambiguus, solitary tract and spinal trigeminal nuclei. Projections were also found into a number of auditory nuclei, namely the nucleus cochlearis-complex, superior olive, ventral and dorsal nuclei of the lateral lemniscus and inferior colliculus. Furthermore, there were projections into the reticular formation of the lateral and dorsocaudal medulla and lateral pons, into nucleus gracilis, inferior and medial vestibular nuclei, lateral reticular nucleus, ventral raphe, pontine gray, superior colliculus, PAG and mediodorsal thalamic nucleus. Injection of the tracer wheat germ agglutinin-conjugated horseradish peroxidase into the ventrolateral pontine vocalization-blocking area in one animal yielded retrograde labeling throughout the PAG. Injection of BDA into a vocalization-eliciting site of the PAG in another animal yielded projections into the ventrolateral pontine vocalization-blocking area. It is concluded that the ventral paralemniscal area in the ventrolateral pons represents a relay station of the descending periaqueductal vocalization-controlling pathway.     

Social status constrains the stress response in the squirrel monkey.

The influence of dominance on the pituitary-adrenal and gonadal systems was evaluated in male squirrel monkeys. Basal and stress levels of plasma cortisol and testosterone were determined in eight male pairs across a 5-week period. The data indicated that squirrel monkeys have unusually high levels of steroid hormones in comparison to other species. Dominant males had higher levels of cortisol and testosterone and showed a smaller stress response than did subordinate males.     

The three-dimensional vestibulo-ocular reflex evoked by high-acceleration rotations in the squirrel monkey

The aim of this study was to determine if the angular vestibulo-ocular reflex (VOR) in response to pitch, roll, left anterior–right posterior (LARP), and right anterior–left posterior (RALP) head rotations exhibited the same linear and nonlinear characteristics as those found in the horizontal VOR. Three-dimensional eye movements were recorded with the scleral search coil technique. The VOR in response to rotations in five planes (horizontal, vertical, torsional, LARP, and RALP) was studied in three squirrel monkeys. The latency of the VOR evoked by steps of acceleration in darkness (3,000°/s² reaching a velocity of 150°/s) was 5.8±1.7 ms and was the same in response to head rotations in all five planes of rotation. The gain of the reflex during the acceleration was 36.7±15.4% greater than that measured at the plateau of head velocity. Polynomial fits to the trajectory of the response show that eye velocity is proportional to the cube of head velocity in all five planes of rotation. For sinusoidal rotations of 0.5–15 Hz with a peak velocity of 20°/s, the VOR gain did not change with frequency (0.74±0.06, 0.74±0.07, 0.37±0.05, 0.69±0.06, and 0.64±0.06, for yaw, pitch, roll, LARP, and RALP respectively). The VOR gain increased with head velocity for sinusoidal rotations at frequencies 4 Hz. For rotational frequencies 4 Hz, we show that the vertical, torsional, LARP, and RALP VORs have the same linear and nonlinear characteristics as the horizontal VOR. In addition, we show that the gain, phase and axis of eye rotation during LARP and RALP head rotations can be predicted once the pitch and roll responses are characterized.This work was supported by NIH grant R01 DC02390     

The effect of superior temporal lesions on the recognition of species-specific calls in the squirrel monkey

Summary Eleven squirrel monkeys (Saimiri sciureus) were trained to discriminate species-specific calls from non-species-specific complex sounds in a go, no-go procedure with social contact as positive reinforcement. The task required that the animals not only responded to a particular call but that this response should be generalized to any squirrel monkey call, whether or not it had been presented previously in training.After having reached a performance level of 75% correct responses in three consecutive sessions, seven animals received bilateral lesions of the auditory cortex; the other four animals served as controls. It was found that small lesions within the superior temporal gyrus did not interfere with the discrimination task. Lesions destroying about three quarters of the auditory cortex led to loss of retention; during retraining the animals did not reach criterion, but performed significantly above chance. These animals were able, however, to master a simplified version of the task where one species-specific call had to be discriminated from one non-species-specific sound. Animals with almost total ablation of the auditory cortex were capable of mastering neither the generalized task nor the simplified version.From these results, together with those of the literature, it is concluded 1) that recognition of complex sounds is not possible after complete auditory cortex ablation, probably because of interference with gestalt-formation processing, and 2) that species-specific calls are processed in the auditory system in the same way as other complex sounds.     

The effect of species-specific vocalization on the discharge of auditory cortical cells in the awake squirrel monkey (Saimiri sciureus)

Summary Action potentials of single auditory cortical neurons of the squirrel monkey were recorded in a chronic, unanesthetized preparation. The responsiveness of units was tested with various types of simple and complex acoustic stimuli in a free field situation. As simple auditory stimuli, bursts of pure tones, clicks, and white noise were utilized. Species-specific vocalizations served as complex, biologically significant stimuli.The data are based on 48 neurons which showed a discrete response to speciesspecific vocalizations. In 63% the response to calls could be predicted from the units' responses to simple stimuli. Thirty-seven percent of the neurons were classified as unpredictable with respect to their responsiveness to vocalizations. The response of most units was restricted to call stimuli which showed similarities in their frequency-time characteristics. About 7% of the 116 units responding to calls were classified as selective responders because they were not excited by any other stimulus tested. It was not possible to single out the acoustic features to which these units responded.Peter Winter died in an skiing accident in March, 1972.     

Canal-otolith interactions driving vertical and horizontal eye movements in the squirrel monkey

The vestibulo-ocular reflex (VOR) was studied in three squirrel monkeys subjected to rotations with the head either centered over, or displaced eccentrically from, the axis of rotation. This was done for several different head orientations relative to gravity in order to determine how canal-mediated angular (aVOR) and otolithmediated linear (lVOR) components of the VOR are combined to generate eye movement responses in three-dimensional space. The aVOR was stimulated in isolation by rotating the head about the axis of rotation in the upright (UP), right-side down (RD), or nose-up (NU) orientations. Horizontal and vertical aVOR responses were compensatory for head rotation over the frequency range 0.25–4.0 Hz, with mean gains near 0.9. The horizontal aVOR was relatively constant across the frequency range, while vertical aVOR gains increased with increasing stimulation frequency. In the NU orientation, compensatory torsional aVOR responses were of relatively low gain (0.54) compared with horizontal and vertical responses, and gains remained constant over the frequency range. When the head was displaced eccentrically, rotation provided the same angular stimuli but added linear stimulus components, due to the centripetal and tangential accelerations acting on the head. By manipulating the orientation of the head relative to gravity and relative to the axis of rotation, the lVOR response could be combined with, or isolated from, the aVOR response. Eccentric rotation in the UP and RD orientations generated aVOR and lVOR responses which acted in the same head plane. Horizontal aVOR-lVOR interactions were recorded when the head was in the UP orientation and facing toward (nose-in) or away from (nose-out) the rotation axis. Similarly, vertical responses were recorded with the head RD and in the nose-out or nose-in positions. For both horizontal and vertical responses, gains were dependent on both the frequency of stimulation and the directions and relative amplitudes of the angular and linear motion components. When subjects were positioned nose-out, the angular and linear stimuli produced synergistic interactions, with the lVOR driving the eyes in the same direction as the aVOR. Gains increased with increasing frequency, consistent with an addition of broad-band aVOR and high-pass lVOR components. When subjects were nose-in, angular and linear stimuli generated eye movements in opposing directions, and gains declined with increasing frequency, consistent with a subtraction of the lVOR from the aVOR. This response pattern was identical for horizontal and vertical eye movements. aVOR and lVOR interactions were also assessed when the two components acted in orthogonal response planes. By rotating the monkeys into the NU orientation, the aVOR acted primarily in the roll plane, generating torsional ocular responses, while the translational (lVOR) component generated horizontal or vertical ocular responses, depending on whether the head was oriented such that linear accelerations acted along the interaural or dorsoventral axes, respectively. Horizontal and vertical lVOR responses were negligible at 0.25 Hz and increased dramatically with increasing frequency. Comparison of the combined responses (UP and RD orientations) with the isolated aVOR (head-centered) and lVOR (NU orientation) responses, indicates that these VOR components sum in a linear fashion during complex head motion.     

Effect of ablation of area postrema on frequency and latency of motion sickness-induced emesis in the squirrel monkey

Twelve young adult squirrel monkeys of the Bolivian subspecies were subjected to continuous counter-clockwise horizontal rotary motion at 25 rpm, together with a simusoidal vertical excursion of 6 in. every 2 sec (0.5 Hz). Each animal was exposed to this motion regimen for a period of 60 min once each week for three consecutive weeks. Following the third weekly motion test bilateral ablation of the area postrema (AP) was performed in eight of the animals by thermal cautery. Two control animals were sham-operated after the third motion test while two additional controls were given the motion tests as noted above but were not operated. The four controls were considered as a single group for statistical analyses of results of the motion tests. After a recovery period of 30 to 40 days, and at a comparable interval in the non-operated controls, each animal was again tested for motion sensitivity for three consecutive weeks. The brains of all of the animals were then fixed by left ventricular cardiac perfusion with Bouin's fluid and processed for histological evaluation of the bilateral AP ablation in comparison with the control brains. Five of the AP-ablated animals postoperatively were completely refractory to the motion stimuli, two exhibited a decreased number of emetic responses, and one exhibited the same number of responses before and after the AP lesions. The controls exhibited no significant difference in emetic sensitivity on the second series of three weekly tests than on the first series. The results of this investigation appear to be in agreement with the observations of Wang and Chinn in the dog [32,33] indicating that the intergrity of the AP (CTZ) is essential to the emetic response to motion.     

Schedule-induced water and ethanol consumption as a function of interreinforcement interval in the squirrel monkey.

Lever pressing of two squirrel monkeys (Saimiri sciureus) was maintained under fixed-interval schedules of food delivery that were varied systematically from 1–10 min. First water and then 2% (V/V) ethanol solutions were available during the experimental sessions at each fixed-interval value. Drinking occurred immediately following the delivery of each pellet. The amount of water consumed increased markedly with increases in the length of the fixed-interval value from 1–9 min; drinking was decreased with one monkey at the 10 min fixed-interval, whereas with the second, drinking continued to increase. The amount of ethanol solution ingested was generally lower than that of water. With one animal ethanol consumption increased when the interval length was increased from 1–6 min, and then decreased beyond this point. With the second animal, ethanol drinking typically increased with increases in the fixed-interval length from 1–10 min. The amount of water consumed in the home cage generally decreased when the interval was lengthened from 1 to approximately 3 min and did not change substantially with further increases in the fixed-interval value.     

Eye movements and vestibular-nerve responses produced in the squirrel monkey by rotations about an earth-horizontal axis

Summary The eye movements produced by constant-speed rotations about an earth-horizontal axis (EHA) are similar in the alert squirrel monkey to those observed in other species. During EHA rotations, there are persistent eye movements, including a nonreversing nystagmus at lower rotation speeds and either a direction-reversing nystagmus or sinusoidal eye movements at higher rotation speeds. Horizontal eye movements are produced by barbecuespit (yaw) rotations, vertical eye movements by head-over-heels (pitch) rotations. The responses can be viewed as composed of a bias component, reflected in the nonreversing nature of the nystagmus, and a cyclic component, reflected in the periodic modulation of slow-phase eye velocity as head position varies. Vestibular-nerve recordings in the barbiturate-anesthetized monkey indicate that neither semicircular-canal nor otolith afferents give rise to a directionally specific dc signal which can account for the bias component. Apparently the appropriate dc signal has to be constructed centrally from a sinusoidal or ac peripheral input. The otolith organs are a likely source of this peripheral input, although contributions from the semicircular canals and from somatosensory receptors must also be considered. Our results suggest that the directional information required to distinguish rotation direction, rather than being contained in the discharge of individual otolith afferents, is encoded across a population of afferents. Possible sources of such information are the phase differences in the sinusoidal responses of otolith afferents differing in their functional polarization vectors.Supported by Grants NS 01330 from the National Institutes of Health and NGR-14-001-225 from the National Aeronautics and Space Administration     

Hormonal responses accompanying fear and agitation in the squirrel monkey

The adrenocortical and gonadal responses of 14 male monkeys were evaluated during four experimental conditions in order to evaluate the influence of social interactions on endocrine responsiveness. Plasma hormone levels were determined during the establishment of social relations, after 60-min exposures to a novel environment, after 60-min exposures to a snake, and 60 min after ACTH administration. Both adrenal and gonadal secretion changed significantly during the first day after social relations were established, although only dominant males showed increases in testosterone, whereas cortisol levels rose in all subjects. Increases in cortisol, but not testosterone, were also observed following exposure to novelty or a snake. The presence of a social partner reduced signs of behavioral disturbance during these test conditions, although the adrenal responses were equivalent or greater than when tested alone. This finding qualifies earlier research which indicated that social support was beneficial for reducing stress when squirrel monkeys were tested in larger groups in their home environment.     

Canal-otolith interactions in the squirrel monkey vestibulo-ocular reflex and the influence of fixation distance

Natural head movements include angular and linear components of motion. Two classes of vestibulo-ocular reflex (VOR), mediated by the semicircular canals and otoliths (the angular and linear VOR, or AVOR and LVOR, respectively), compensate for head movements and help maintain binocular fixation on targets in space. In this study, AVOR/LVOR interactions were quantified during complex head motion over a broad range of fixation distances at a fixed stimulus frequency of 4.0 Hz. Binocular eye movements were recorded (search-coil technique) in squirrel monkeys while fixation distance (assessed by vergence) was varied using brief presentations of earth-fixed targets at various distances. Stimuli consisted of rotations around an earth-vertical axis and therefore always activated the AVOR. Horizontal and vertical AVORs were assessed when the head was centered over the axis of rotation and oriented upright (UP) and right-side-down (RD), respectively. AVOR gains increased slightly with increasing vergence in darkness, as expected given the small anterior position of the eyes in the head. Combined AVOR/LVOR responses were recorded when subjects were displaced eccentrically from the rotation axis. Eccentric rotations activated the AVOR just as when the head was centered, but added a translational stimulus which generated an LVOR component in response to interaural (IA) or dorsoventral (DV) tangential accelerations, depending on whether the head was UP or RD, respectively. When the head was eccentric and facing nose-out, the AVOR and LVOR produced ocular responses in the same plane and direction (coplanar and synergistic), and response magnitudes increased with increasing vergence. With the head facing nose-in, AVOR and LVOR response components were oppositely directed (coplanar and antagonistic). The AVOR dominated the response when fixation distance was far, and phase was compensatory for head rotation. As fixation distance decreased toward the rotation axis, responses declined to near zero, and when fixation distance approached even closer, the LVOR component dominated and response phase inverted. The same pattern was observed for both horizontal (head UP) and vertical (head RD) responses. The LVOR was recorded directly by rotating subjects eccentrically but in the nose-up (NU) orientation. The AVOR then generated torsional responses to head roll, coexistent with either horizontal or vertical LVOR responses to tangential acceleration when the subject was oriented head-out or right-side-out, respectively. Only the LVOR response components were modulated by vergence. A vectorial analysis of AVOR, LVOR, and combined responses supports the conclusion that AVOR and LVOR response components combine linearly during complex head motion. Received: 27 February 1997 / Accepted: 18 June 1997     

Histochemical mapping of succinic dehydrogenase and cytochrome oxidase in the pons and mesencephalon of squirrel monkey (Saimiri sciureus)

Summary The distribution of succinic dehydrogenase (SDA) and cytochrome oxidase (Cy. O) has been investigated in a series of sections through the pons and mesencephalon of the squirrel monkey brain. The localization of the two enzymes is very similar in the various regions and shows only slight differences. The epiphysis, however, shows moderately strong SDA and very mild Cy. O activity. Particularly strong SDA and Cy. O activity has been observed in the cell bodies of the various cranial nerve nuclei, nucleus colliculi inferioris, colliculi superioris, nuclei griseum pontis, reticularis tegmenti pontis, lemnisci lateralis pars dorsalis, geniculatum laterale and mediale, and pulvinaris. The enzyme content of the neurons and cell bodies is generally stronger compared to the neuropil which often occurs in smooth, loose, compact and reticulated forms. Any special relationship between the neurons and neuropil with regard to their enzyme content has, however, not been observed. The cranial nerves, and fibers of the brachium conjunctivum, corpus callosum, and fornix show very mild enzyme activity except those of the trapezoid complex which show moderate enzyme activity.Abbreviations Ann Nucleus annularis - APT Area praetectalis - AS Aquaeductus Sylvii - BC Brachium conjunctivum - BCI Brachium colliculi inferioris - BCS Brachium colliouli superioris - BP Brachium pontis - Cb Cerebellum - CC Corpus callosum - CCI Commissura colliculi inferioris - CCS Commissura colliculi superioris - Cd Nucleus caudatus - CHD Commissura hippocampi —parsdorsalis - CoI Colliculus inferior - CoP Commissura posterior - CoR Corona radiata - CoS Colliculus superior - CPf Cortex piriformis - CR Cortex retrosplenialis - DBC Decussatio brachii conjunctivi - DG Nucleus dorsalis tegmentalis(Gudden) - DR Nucleus dorsalis raphes - EP Epiphysis - F Fornix - FH Fimbria hippocampi - FLM Fasciculus longitudinalis medialis - FRPC Formatio reticularis pontis, parscaudalis - FRPO Formatio reticularis pontis, parsoralis - FRTM Formatio reticularis tegmentimesencephali - GC Substantia grisea centralis - GCd Substantia grisea centralis, parsdorsalis - GCv Substantia grisea centralis, parsventralis - GL Corpus geniculatum laterale - GM Corpus geniculatum mediate - GPO Griseum pontis - Hipp Hippocampus - HL Nucleus habenulae lateralis - HM Nucleus habenulae medialis - IP Nucleus interpeduncularis - LC Nucleus locus coeruleus - LCb Lingula cerebelli - Lim Nucleus limitans thalami - LL Lemniscus lateralis - LLD Nucleus lemnisci lateralis —parsdorsalis - LM Lemniscus medialis - LP Nucleus lateralis posterior thalami - MD Nucleus medialis dorsalis thalami - Mv Nucleus motorius n. trigemini - NCI Nucleus colliculi inferioris - NCS Nucleus centralis superior tegmenti - NCT Nucleus trapezoideum - NMv Nucleus tractus mesencephalicus n.trigemini - NR Nucleus ruber - NST Nucleus supratrochlearis - NSv Nucleus tractus spinalis n. trigemini - NiiiC Nucleus centralis n. oculomotorii - NiiiD Nucleus n. oculomotorii — pars dor-salis - NiiiV Nucleus n. oculomotorii — pars ven-tralis - Niv Nucleus n. troehlearis - nvm Nervus trigeminus, portio major - niv Nervus trochlearis - nvi Nervus abducens - OS Nucleus olivaris superior - P Nucleus posterior thalami - PbL Nucleus parabrachialis lateralis - PbM Nucleus parabrachialis medialis - PC Pedunculus cerebri - Pg Nucleus parabigeminalis - PUI Nucleus pulvinaris inferior thalami - PUL Nucleus pulvinaris lateralis thalami - PUM Nucleus pulvinaris medialis thalami - Py Tractus pyramidalis - Pv Nucleus principalis n. trigemini - R Nucleus reticularis thalami - RTP Nucleus reticularis tegmenti pontis - SNc Substantia nigra — pars compacta - SNd Substantia nigra — pars diffusa - Sub Subiculum - TCT Tractus corticotectalis - VR Nucleus ventralis raphes - III Ventriculus tertius - IV Ventriculus quartus     

Histochemical mapping of succinic dehydrogenase and cytochrome oxidase in the spinal cord, medulla oblongata and cerebellum of squirrel monkey (Saimiri sciureus)

Summary The distribution of succinic dehydrogenase (SDA) and cytochrome oxidase (Cy. O) in serial sections of the cervical region of the spinal cord and the medulla oblongata, arranged caudo-cranially, has been described. The motor cranial nerve nuclei exhibit strong SDA and Cy. O activity in the neurons and neuropil. The nuclei gracilis, cuneatus, olivaris inferior, cochlearis and vestibularis likewise show strong enzyme activity. Nucleus intercalatus and nucleus tractus solitarius, however, show weak and moderate enzyme activity respectively. The lateral part of formatio reticularis myelencephali shows less SDA and Cy. O compared to the medial part, which shows some accumulation of these enzymes in the neuropil.The neuropil of the molecular layer of cerebellar cortex and the perikarya and dendrites of the Purkinje cells show strong SDA and Cy. O activity. The granular layer exhibits stronger SDA and Cy. O in the synaptic glomeruli. The cerebellar nuclei possess stronger enzyme activity in the neurons and dendritic branches, compared to mild activity in the neuropil.Abbreviations AB Nucleus ambiguus - AP Area postrema - Cb Cerebellum - Cn Nucleus cuneatus medialis - CnL Nucleus euneatus lateralis - CRF Corpus restiforme - D Cell group D of meesen and Olszewski (1949) - DPy Decussatio pyramidum - DV Nucleus dorsalis n. vagi - F Cell group P of Meesen and Olszewski (1949) - FC Puniculus cuneatus - FG Funiculus gracilis - FLM Fasciculus longitudinalis medialis - FRM Formatio reticularis myelencephali - G Nucleus gracilis - Gr Granular layer of cerebellar cortex - I Nucleus intercalatus - Lcb Lingula cerebelli - MoL Molecular layer of cerebellar cortex - NC Nucleus cochlearis - NCD Nucleus cochlearis dorsalis - NCV Nucleus cochlearis ventralis - ND Nucleus dentatus - NE Nucleus emboliformis - NF Nucleus fastigii - NFL Nerve fiber layer - NG Nucleus globosus - NR Nucleus raphes - NSV Nucleus tractus spinalis n. trigemini - NTS Nucleus tractus solitarius - NVI Nucleus n. abducentis - NVII Nucleus n. facialis - NXII Nucleus n. hypoglossi - OI Nucleus olivaris inferior - OIm Nucleus olivaris inferior, accessorius medialis - OIp Nucleus olivaris inferior, principalis - P Layer of Purkinje cells - Pp Nucleus praepositus - Py Tractus pyramidalis - RG Nucleus reticularis gigantocellularis - RL Nucleus reticularis lateralis myelencephali - RPM Nucleus reticularis paramedianus myelencephali - SGD Nucleus substantiae griseae dorsalis - SGL Nucleus substantiae griseae lateralis - SGV Nucleus substantiae griseae ventralis - TCV Tractus corticospinalis ventralis - TS Tractus solitarius - TSC Tractus spinocerebellaris - VI Nucleus vestibularis inferior - VL Nucleus vestibularis lateralis - VM Nucleus vestibularis medialis - VS Nucleus vestibularis superior - IV Ventriculus quartus     

Influence of static head position on the horizontal nystagmus evoked by caloric,rotational and optokinetic stimulation in the squirrel monkey

Summary We studied the influence of static head position on the horizontal nystagmus produced by caloric, rotational and optokinetic stimulation in alert squirrel monkeys. Caloric nystagmus is stronger for nose up (NU) than for nose down (ND) pitches; so, for example, slow-phase eye velocity is four times larger in supine than in prone positions. A similarly directed asymmetry occurs in the horizontal vestibulo-ocular (HVOR) responses to longduration, constant angular-head accelerations, but not to midband (0.1 Hz) sinusoidal head rotations. Consistent with a first-order model of the HVOR, the low-frequency or acceleration gain of the reflex (G_A) is equal to the product of the midband velocity gain (G_V) and a time constant (T_VOR). G_V is proportional to the cosine of the angle between the horizontal-canal plane and the plane of rotation, from which it is concluded that signals from the horizontal, but not from the vertical canals contribute to the HVOR. T_VOR can be as much as twice as large in NU than in ND positions. G_A is proportional to T_VOR and it, too, shows a NU-ND asymmetry. The time constant of optokinetic afternystagmus (T_OKAN) was also studied. Since T_VOR and T_OKAN are modified in similar ways by static tilts, it is concluded that head position affects the time constants by way of velocity-storage mechanisms. Evidence is presented that the position-dependent modification of velocity storage is otolith-mediated. The results are used to analyze the mechanisms of caloric nystagmus. The caloric response consists of a convective component (C_C), as originally envisioned by Bárány (1906), and a nonconvective component (N_C). C_C accounts for 75% of the caloric response in the conventional supine testing position. Both components can be affected by the position-dependent modification of T_VOR or, equivalently, of G_A. It has been suggested that two mechanisms might contribute to N_C: 1) a direct thermal effect on hair cells or afferents; or 2) a thermal expansion of labyrinthine fluids that results in a cupular displacement. Both theoretical and experimental evidence indicates that only the first of these mechanisms could result in the steady-state caloric response that is observed in the absence of convection (e.g., in spaceflight and after canal plugging) and that contributes to the prone-supine asymmetry seen in caloric testing.     

Connections between the lacrimal gland and sensory trigeminal neurons: a WGA/HRP study in the cynomolgous monkey

The sensory innervation of the lacrimal gland (LG) in the cynomolgous monkey was studied using the retrograde wheat germ agglutinin/horsereadish peroxidase (WGA/HRP) tracer technique. A small solidified piece of WGA/HRP was implanted in the LG. Labelled sensory first-order neurons were found in the ipsilateral trigeminal ganglion (TG) and in the ipsilateral mesencephalic trigeminal nucleus (MTN). The distribution of labelled TG neurons was restricted to ophthalmic and maxillary ganglionic parts. Sensory innervation of LG by primary afferents is not only restricted to TG; an MTN involvement has also been found. This may imply that there is a central sensory role in the production and release of tears.