Respiratory movements during vocalization in the squirrel monkey

Respiratory abdominal movements during vocalization were measured in awake squirrel monkeys during spontaneous and playback-induced vocal activity. Large vocalization-correlated respiratory movements (VCRM) starting before vocalization were observed during several call types, such as peeping, trilling, cackling and err-chuck. Purring, in contrast, was accompanied by only small VCRM that started late after vocal onset. VCRM during trilling, a call with marked frequency modulation, showed a modulation in the rhythm of the frequency changes. A correlation with amplitude modulation was also present but more variable. As high frequencies need a higher lung pressure for production than low frequencies, the modulation of VCRM seems to serve to optimize the lung pressure in relation to the vocalization frequency. The modulation, furthermore, may act as a mechanism to produce different trill variants. During err-chucks and staccato peeps, which show a large amplitude modulation, a non-modulated VCRM occurred. This indicates the existence of a laryngeal amplitude-controlling mechanism that is independent of respiration.Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Serum hormone patterns during abortion in the Bolivian squirrel monkey

Serum measurements of chorionic gonadotropin (CG), estradiol (E-2) and progesterone (P) were used to describe patterns of hormonal change in Bolivian squirrel monkeys undergoing spontaneous abortion. During early pregnancy, serum CG levels gradually increased, reaching maximum levels at the end of the first 50 days of pregnancy (range: 200-1964 ug protein/ml). E-2 concentrations also increased to high levels (10-30 ng/ml) toward the end of pregnancy, while serum P remained fairly constant at levels above 100 ng/ml. A gradual decline in serum hormone concentrations was observed in aborting animals. CG levels declined to less than 100 ug protein/ml while E-2 and P decreased to concentrations characteristic of nonpregnant cycling animals, less than 500 pg/ml and 20 ng/ml respectively. The data suggest that two weekly measurements of CG and E-2 could be used to identify monkeys undergoing abortion and those which have already aborted.     

Cortical potentials associated with vocalization in the rhesus monkey.

Cortical potentials associated with vocalization have been investigated in two rhesus monkeys. In both animals a slow negative potential shift beginning approximately 1 sec prior to the onset of vocalization has been observed in transcortical recordings from precentral areas. It is suggested that this slow potential change might be the phylogenetic antecedent of the voluntary control of speech in humans.     

Diurnal and annual variation of adrenocortical activity in the squirrel monkey

Diurnal changes in basal cortisol levels and stress reactivity were assessed in male and female squirrel monkeys. Blood samples were collected at four-hour intervals throughout the day and night in the mating and nonmating seasons. Basal cortisol levels in females were similar in both seasons, but males tended to have higher cortisol levels during the mating season, especially at night. For both sexes, cortisol secretion was highest between 0400 and 0800 preceding the onset of the diurnal activity period. Assessment of cortisol responses following brief handling and anesthesia indicated that stress responses were relatively stable across the year, but cortisol increments were slightly higher in the nonmating season. Cortisol levels post-stress were generally related to prior baseline values. Thus, a knowledge of biorhythmic changes in basal hormone levels was important for predicting hormone levels after acute stressors. Males also underwent marked seasonal variation in their basal testosterone levels, which markedly altered the nature of their testosterone responses 30-minutes poststress. © 1995 Wiley-Liss, Inc.     

Visual sensitivity in the squirrel monkey

Several indices of visual sensitivity have been obtained from behavioral experiments conducted on the squirrel monkey (Saimiri sciureus). In this species, the photopic spectral sensitivity functions determined by increment-threshold and flicker discrimination procedures are substantially different; the involvement of two different neural processes in the two tasks is suggested. When tested similarly, the thresholds for rod and cone-based vision are not substantially different for squirrel monkeys and humans; however, above cone threshold, for a 500 nm test light, increment threshold is some 0.3 to 0.4 log₁₀ units higher for the squirrel monkey. Rod saturation has also been demonstrated to occur in the squirrel monkey.     

Physiological effects of cocaine in the squirrel monkey.

Doses of cocaine that have previously been shown to have behavioral effects produced dose-related increases in arterial blood pressure, heart rate and core temperature in unanesthetized squirrel monkeys ($\text{Saimiri}$$\text{sciureus}$). The pressor effect was immediate, but heart rate increased more gradually after cocaine injection. The onset of hyperthermia was substantially delayed. The squirrel monkey may be a good animal model of the physiological concomitants of cocaine abuse in humans.     

Orthocephalization in the postweaning squirrel monkey

Twenty male squirrel monkeys (Saimiri sciureus boliviensis) raised in captivity were allotted to one of the following groups: weanling control (C6) sampled at 6 months of age; young control (C24) fed ad libitum on a control diet and killed at 24 months of age; and malnourished (M24) fed ad libitum on a low-protein diet and sampled at 24 months of age. Cranial points and the lateral semicircular canals were marked. On each skull, a strict lateral teleradiograph was taken, and the lengths of the midsagittal chords and their angles with respect to the vestibular line were measured. Age changed the lengths in about 70% of the chords and more than 50% of the angles. Malnutrition arrested about 50% of the lengths, but the angles were practically not affected. It is concluded that the postweaning Saimiri sciureus undergoes orthocephalization according to a general pattern already observed in rodents and suggested for pongids. Postweaning malnutrition affected growth in size but not shape changes related to the orthocephalization of the Saimiri skull. © 1996 Wiley-Liss, Inc.     

Craniorachischisis in a squirrel monkey

A stillborn squirrel monkey had craniorachischisis. The calvarium was absent and the skin and vertebral neural arches were cleft from the foramen magnum to the midlumbar region. Cranial nerves and degenerating neural tissue were attached to the cranial base and there were remnants of spinal cord in skin-covered areas of the spinal canal. The adrenal glands were normal. This is the only reported case of craniorachischisis in a monkey fetus.     

Auditory frequency discrimination in the squirrel monkey

Four squirrel monkeys (Saimiri sciureus) were tested for their frequency discrimination capacity using an eyeblink classical conditioning procedure, with air puff against the eye as unconditioned stimulus and 600-ms pure tones as conditioned stimuli. Absolute frequency difference thresholds showed a minimum (20-41 Hz, mean 30 Hz) at 4,000-8,000 Hz and increased towards higher as well as lower frequencies (70-90 Hz, mean 80 Hz at 300 Hz; 44-120 Hz, mean 82 Hz at 16,000 Hz). Relative frequency difference thresholds increased from higher to lower frequencies, with values as low as 0.3-0.8% (mean 0.5%) at 16,000 Hz and as large as 24-30% (mean 27%) at 300 Hz. The squirrel monkey's frequency discrimination function thus shows a severe deviation from Weber's law. The frequency difference thresholds are comparable to human's in the 4,000-8,000 Hz range, but are 65-80 times higher in the 500- to 300-Hz range. Individuals with high auditory thresholds do not necessarily also have high frequency difference thresholds.     

Acoustic structure of vocalization and stapedius muscle activity during vocal development in chickens (Gallus gallus)

The link between stapedius muscle activity and acoustic structure of vocalization was analysed in cocks of age 20–30 to 90–100 days old. The results show that stapedius muscle activation depends on the acoustic structure of vocalization and changes during vocal development. This dependence was observed in spontaneous calls and in vocalizations elicited by stimulating the mesencephalic calling area. In 30-day-old cocks stapedius muscle EMG response is never associated with vocalizations with an acoustic energy content which is always distributed at frequencies higher than 2000 Hz. The coupling between vocalization and stapedius muscle activity begins later, when birds produce vocalizations with acoustic energy shifted towards lower frequencies. Overall, stapedius muscle activity is related to a bird's production of high amplitude low frequencies. These results support the hypothesis that the primary role of the stapedius muscle during normal vocal development is to dampen the amplitude of low frequency energy that reaches the cochlea during vocalization.     

An immunoradiometric assay for squirrel monkey prolactin.

Determination of immunoreactive prolactin in squirrel monkeys has been hampered by the lack of specific antibodies. We investigated the adaptability of a commercially available immunoradiometric assay for human prolactin, which employs two separate monoclonal antibodies (MAb I and II) to human prolactin, to determine the presence of squirrel monkey prolactin. We found that immunoreactivity curves for prolactin in squirrel monkey pituitary homogenates and serum were parallel to human prolactin standards, suggesting that the epitopes recognized by these antibodies were common to both human and squirrel monkey prolactin. Both nonglycosylated (23 kD) and glycosylated (26 kD) forms of squirrel monkey prolactin were detected in squirrel monkey pituitary homogenates by Western blot analysis using [125I]-MAb II. Neither sheep nor rat prolactin was recognized by Western blot analysis, indicating that the assay may be specific for primate prolactins. We examined the effect of ketamine HCl, an anesthetic that has been shown to elevate serum prolactin levels in other primates, on prolactin secretion in squirrel monkeys. Serum prolactin levels increased greater than fourfold after the administration of ketamine HCl (30 mg/kg b.w., i.m.) compared with control levels. Serum prolactin levels were unaffected by anesthesia with pentobarbital sodium (15 mg/kg b.w., i.v.). This assay provides a reliable and sensitive method for determining immunoreactive squirrel monkey prolactin.     

Effects of phencyclidine and ketamine on cardiovascular activity and temperature in the squirrel monkey

Heart rate (HR), mean arterial blood pressure (BP) and core temperature (TEMP) were recorded from chair-restrained squirrel monkeys surgically prepared with chronically indwelling arterial and venous catheters to determine the effects of acute intravenous (i.v.) injections of phencyclidine and ketamine and intramuscular (i.m.) injections of ketamine. Phencyclidine (0.03-3.0 mg/kg) and ketamine (0.3-30.0 mg/kg) i.v. increased BP and decreased TEMP, and the changes in BP and in TEMP were greater in magnitude and duration after phencyclidine. Heart rate also increased monotonically after 0.03-0.3 mg/kg phencyclidine or 0.3-10.0 mg/kg ketamine, but the effects of higher doses of either drug were biphasic with decreases followed by increases in HR. When either of two doses of ketamine (10.0 and 30.0 mg/kg) was injected i.m., the effects were qualitatively similar to those observed after i.v. administration although of much less magnitude, and there was no evidence of a biphasic change in HR. The data show that these two dissociative anesthetics differ in duration of action and in magnitude of effect on cardiovascular activity and core temperature in the squirrel monkey, and that phencyclidine is approximately ten times as potent as ketamine.     

Respiratory muscle control during vomiting

The changes in thoracic and abdominal pressure that generate vomiting are produced by coordinated action of the major respiratory muscles. During vomiting, the diaphragm and external intercostal (inspiratory) muscles co-contract with abdominal (expiratory) muscles in a series of bursts of activity that culminates in expulsion. Internal intercostal (expiratory) muscles contract out of phase with these muscles during retching and are inactive during expulsion. The periesophageal portion of the diaphragm relaxes during expulsion, presumably facilitating rostral movement of gastric contents. Recent studies have begun to examine to what extent medullary respiratory neurons are involved in the control of these muscles during vomiting. Bulbospinal expiratory neurons in the ventral respiratory group caudal to the obex discharge at the appropriate time during (fictive) vomiting to activate either abdominal or internal intercostal motoneurons. The pathways that drive phrenic and external intercostal motoneurons during vomiting have yet to be identified. Most bulbospinal inspiratory neurons in the dorsal and ventral respiratory groups do not have the appropriate response pattern to initiate activation of these motoneurons during (fictive) vomiting. Relaxation of the periesophageal diaphragm during vomiting could be brought about, at least in part, by reduced firing of bulbospinal inspiratory neurons.     

Time-course effects of two barbiturates on cardiovascular activity and temperature in the squirrel monkey

Heart rate (HR), mean arterial blood pressure (BP) and core temperature (TEMP) were recorded from conscious, chair-restrained squirrel monkeys surgically prepared with chronically indwelling arterial and venous catheters to determine the effects of acute intravenous injections of methohexital and secobarbital. Methohexital (0.3–17.0 mg/kg) and secobarbital (1.0–30.0 mg/kg) decreased HR, BP and TEMP in a dose-dependent manner. Methohexital resulted in a greater decrease in blood pressure than secobarbital, but the latter caused greater decreases in heart rate and temperature. The duration of all effects of methohexital was substantially briefer than the effects of secobarbital at the higher doses studied. The data show that these two barbiturates differ not only in duration of action but also in the magnitude of effect on cardiovascular activity in the squirrel monkey.