Male Bonnet Research Articles

Effect of Chlordiazepoxide or Haloperidol Oral Premedication during Midazolam-Ketamine Anaesthesia on Physiological and Blood Gas Parameters in Adult Male Bonnet Macaques (Macaca radiata)

Capturing wild animals with minimal stress is crucial to reduce morbidity and mortality. Oral premedicants can ease handling and subsequent anaesthetic administration. This study evaluated anaesthetic protocols and physiological changes during vasectomy in 12 adult male Bonnet Macaques. Group I received 10 mg/kg chlordiazepoxide, and Group II received 1 mg/kg haloperidol orally four hours before midazolam-ketamine anaesthesia. Sedation quality, induction, maintenance, and recovery were assessed. Physiological and blood gas changes were monitored at 0, 5, 10, 15, and 20 minutes. Both groups exhibited sedation post-premedication. Induction, maintenance, and anaesthesia depth were similar. Group I had better analgesia, while Group II had superior muscle relaxation. Blood gas analysis indicated mild stress and respiratory acidosis in both groups, with Group II showing more significant hypoxemia and respiratory acidosis. Haloperidol-premedicated animals were easier to handle but exhibited increased stress parameters compared to chlordiazepoxide-premedicated animals. Recovery was better in Group I. Both protocols effectively induced sedation and anaesthesia in Bonnet Macaques.

Recovery of Accidental Traumatic Brain Injury (TBI) in an Infant Bonnet Macaque (Macaca radiata) by Progesterone Therapy

An infant male bonnet macaque with a history of accident and lateral recumbency presented to the Veterinary Clinical Complex, VCRI, Orathanadu. On examination he scored a 10 on the modified Glasgow Coma Scale (GCS), and the animal had racoon eyes. Immediately skull X-ray was taken and it revealed two radiating temporal bone fracture. These characteristics strongly pointed to a tentative diagnosis of Traumatic Brain Injury. In addition to supportive care, Progesterone, a neuroprotective steroid, was continuously administered to the animal at a dose rate of 0.2 mg per kg SID P.O. In order to manage and monitor the animal health, it was admitted to the critical care unit. On the tenth day, the animal showed slight improvement and had hemiparesis on the contralateral side of the cranial lesion. The animal's limb reflexes were fully restored by day 20. However cerebral and vestibular lesions persisted with signs of blindness, nystagmus, and circling. After 60 days of continuous treatment animal recovered uneventfully.

Surgical Repair of Indirect Inguinal Hernia in Bonnet Macaque (Macaca radiata)

Background:Hernia is a protrusion of an organ from the wall of the cavity bearing it. Omentum, adipose tissue, and intestinal loops are the most frequently involved organs. The present case report is a rare case of indirect inguinal hernia having omentum engaged in scrotum through hernial ring in a bonnet macaque (Macaca radiata) and its surgical management.Case Description:A 19-year-old male bonnet macaque was presented with distension of the right inguinal and scrotal region. Physical examination revealed an inguinal hernia. Surgical intervention was deemed necessary considering the state of the animal. The herniation was surgically corrected by the removal of the protruded fatty mass. The monkey was kept in strict confinement till complete healing. The animal recovered uneventfully in 2 weeks without any post-operative complications. This case report details a successful surgical repair of an indirect inguinal hernia in a bonnet macaque.Conclusion:Based on the present case study, it is concluded that surgery can be an ideal and effective option for the treatment of inguinal hernias in primates.

Normalization by valence and motivational intensity in the sensorimotor cortices (PMd, M1, and S1)

Our brain’s ability to represent vast amounts of information, such as continuous ranges of reward spanning orders of magnitude, with limited dynamic range neurons, may be possible due to normalization. Recently our group and others have shown that the sensorimotor cortices are sensitive to reward value. Here we ask if psychological affect causes normalization of the sensorimotor cortices by modulating valence and motivational intensity. We had two non-human primates (NHP) subjects (one male bonnet macaque and one female rhesus macaque) make visually cued grip-force movements while simultaneously cueing the level of possible reward if successful, or timeout punishment, if unsuccessful. We recorded simultaneously from 96 electrodes in each the following: caudal somatosensory, rostral motor, and dorsal premotor cortices (cS1, rM1, PMd). We utilized several normalization models for valence and motivational intensity in all three regions. We found three types of divisive normalized relationships between neural activity and the representation of valence and motivation, linear, sigmodal, and hyperbolic. The hyperbolic relationships resemble receptive fields in psychological affect space, where a unit is susceptible to a small range of the valence/motivational space. We found that these cortical regions have both strong valence and motivational intensity representations.

Lifelong reductions of PKMζ in ventral hippocampus of nonhuman primates exposed to early-life adversity due to unpredictable maternal care.

Protein kinase Mζ (PKMζ) maintains long-term potentiation (LTP) and long-term memory through persistent increases in kinase expression. Early-life adversity is a precursor to adult mood and anxiety disorders, in part, through persistent disruption of emotional memory throughout life. Here we subjected 10- to 16-wk-old male bonnet macaques to adversity by a maternal variable-foraging demand paradigm. We then examined PKMζ expression in their ventral hippocampi as 7- to 12-yr-old adults. Quantitative immunohistochemistry reveals decreased PKMζ in dentate gyrus, CA1, and subiculum of subjects who had experienced early-life adversity due to the unpredictability of maternal care. Adult animals with persistent decrements of PKMζ in ventral hippocampus express timid rather than confrontational responses to a human intruder. Persistent down-regulation of PKMζ in the ventral hippocampus might reduce the capacity for emotional memory maintenance and contribute to the long-lasting emotional effects of early-life adversity.

Gender differential in profitability of cultivating Scotch bonnet pepper

ABSTRACT Profitability difference may exist across farmers’ gender. This study examined profitability differences of male and female Scotch bonnet pepper (Capsicum annuum L.) farmers, levels of profitability of Scotch bonnet pepper cultivation, comparison of production cost, output and profit, and identified factors affecting profitability in Scotch bonnet pepper production. Data from respondents obtained through multi-stage sampling were analyzed with descriptive and budgetary techniques. There was a mean gross margin (GM) of N42,126 for male and N16,929 for female farmers; N is the Naira, Nigerian currency, 1 USD = N300. The GM ratio was 0.81 and 0.91 for male and female farmers, respectively. Rates of return on investment were 23.8% for male and 9.5% for female; profit was N23,796 for males and N8,016 for female farmers. A difference occurred across gender in mean production cost per land area (N100,025.33 for males and N84,260.58 for females), output (375.55 kg for males and 286.62 kg for females), and profit (N23,789.00 for males and N8,016.35 for females). For both genders, profitability of Scotch bonnet pepper cultivation was mostly affected by poor pricing (96.0% for males and 100.0% of females), poorly organized market (88.0% for males and 100.0% of females), scarcity of improved inputs (76.0% of males and 80.8% of females), problem of pests and diseases (77.3% of males and 80.8% of females). Profitability level of Scotch bonnet pepper cultivation, especially for female farmers can be improved through adequate training and access to funds for purchasing basic production inputs and facilitating adequate market linkages.

Patterns of anterior versus posterior white matter fractional anistotropy concordance in adult nonhuman primates: Effects of early life stress

IntroductionFunctional neuroimaging studies report global prefrontal dysconnectivity in mood disorders, supporting the notion of widespread disruptions in brain networks. Microscopic alterations in white matter (WM) tracts – which possess neuroplastic properties and play a central role in brain connectivity – are interrogated herein in the context of brain dysconnectivity. Early life stress (ELS), an antecedent to human mood disorders, induces WM alterations in volumetrics and integrity. We hypothesized that nonhuman primate infants exposed to ELS would exhibit persistent impairments in both frontal and posterior concordance of WM integrity, therefore contributing to global brain dysconnectivity. MethodsUsing a 3T MRI, diffusion tensor imaging (DTI) was performed on 21 adult male Bonnet macaques, 12 of whom had been raised under variable foraging demand (VFD) conditions and nine of whom had been raised under normative conditions (Non-VFD). As representative of anterior regions, fractional anisotropy (FA) concordance between anterior corpus callosum (ACorpusC) and anterior limb of the internal capsule (ALIC) was examined. For posterior regions, FA concordance between posterior corpus callosum (PCorpusC) and posterior limb of the internal capsule (PLICA) and between PCorpusC and occipital WM was examined. Examination of posterior FA was explored in the context of frontal markers of neuroplasticity. ResultsA concordant relationship for FA between left ALIC and ACorpusC was evident in Non-VFD-reared subjects, but significantly absent in VFD-reared subjects. For left posterior regions, FA concordance between PLICA and PCorpusC and occipital WM and PCorpusC was evident in VFD-reared and not Non-VFD-reared subjects. The posterior concordance in VFD was significantly distinguishable from the deficit in anterior concordance FA in VFD. ConclusionsThe findings support the view that disrupted emotional integrity of the maternal-infant attachment process affects normative synchronous development of frontal white matter tracts but creates errant posterior concordance and also disrupts an inverse relationship between posterior white matter tracts and markers of neuroplasticity. We provide preliminary evidence that a concordant relationship between capsular–callosal FA may become discordant, providing a putative mechanism for prefrontal functional brain dysconnectivity.

Spatial memory in nonhuman primates implanted with the subdural pharmacotherapy device

This study investigated the possible influence of the Subdural Pharmacotherapy Device (SPD) on spatial memory in 3 adult, male bonnet macaques (Macaca radiata). The device was implanted in and above the subdural/subarachnoid space and cranium overlaying the right parietal/frontal cortex: a circuitry involved in spatial memory processing. A large test chamber, equipped with four baited and four non-baited food-ports at different locations, was used: reaches into empty food ports were counted as spatial memory errors. In this study of within-subject design, before SPD implantation (control) the animals made mean 373.3±114.9 (mean±SEM) errors in the first spatial memory test session. This value dropped to 47.7±18.4 by the 8th session. After SPD implantation and alternating cycles of transmeningeal saline delivery and local cerebrospinal fluid (CSF) drainage in the implanted cortex the spatial memory error count, with the same port locations, was 33.0±12.2 during the first spatial memory test session, further decreasing to 5.7±3.5 by the 8th post-implantation session (P<0.001 for trend). Replacing transmeningeal saline delivery with similar delivery of the GABAA receptor agonist muscimol (1.0mM) by the SPD did not affect the animals’ spatial memory performance, which in fact included at least one completely error-free session per animal over time. The study showed that complication-free implantation and use of the SPD over the parietal and frontal cortices for months leave spatial memory processes intact in nonhuman primates.

Glucagon-like peptide-1 as predictor of body mass index and dentate gyrus neurogenesis: neuroplasticity and the metabolic milieu.

Glucagon-like peptide-1 (GLP-1) regulates carbohydrate metabolism and promotes neurogenesis. We reported an inverse correlation between adult body mass and neurogenesis in nonhuman primates. Here we examine relationships between physiological levels of the neurotrophic incretin, plasma GLP-1 (pGLP-1), and body mass index (BMI) in adolescence to adult neurogenesis and associations with a diabesity diathesis and infant stress. Morphometry, fasting pGLP-1, insulin resistance, and lipid profiles were measured in early adolescence in 10 stressed and 4 unstressed male bonnet macaques. As adults, dentate gyrus neurogenesis was assessed by doublecortin staining. High pGLP-1, low body weight, and low central adiposity, yet peripheral insulin resistance and high plasma lipids, during adolescence were associated with relatively high adult neurogenesis rates. High pGLP-1 also predicted low body weight with, paradoxically, insulin resistance and high plasma lipids. No rearing effects for neurogenesis rates were observed. We replicated an inverse relationship between BMI and neurogenesis. Adolescent pGLP-1 directly predicted adult neurogenesis. Two divergent processes relevant to human diabesity emerge—high BMI, low pGLP-1, and low neurogenesis and low BMI, high pGLP-1, high neurogenesis, insulin resistance, and lipid elevations. Diabesity markers putatively reflect high nutrient levels necessary for neurogenesis at the expense of peripheral tissues.

Low respiratory quotients in chow‐fed male bonnet macaque monkeys as an indicator of metabolic stress due to single cage housing

ObjectiveDetermine the metabolic affects of previously group housed male monkeys residing in single cage housing (SCH).MethodsAfter two months of SCH, 16 adult male bonnet macaque (M. radiata) monkeys (11.0 ± 1.9 kg, modified BMI = 40.0 ± 7.0 kg/crown‐rump length, m2 and 14.5 ± 3.1 years old) were each placed in the primate Enhanced Metabolic Testing Activity Chamber (EMTAC Inc. Santa Barbara, CA) for 22‐hour measurements of energy intake (kcal/kg) and expenditure (EE; kcal/kg/min), along with the respiratory quotient (RQ;VCO2/VO2). All were fed monkey chow #5038 (LabDiet Inc., Richmond, IN) ad‐libitum under a 12/12 hour light/dark cycle. Metabolic data were divided into day (8‐hours), night (12‐hours) and morning periods (2‐hours). For data analysis (SPSS Ver. 13), monkeys were divided into stressed and non‐stressed groups based on their RQ being above or below 0.70, respectively.ResultsWhen compared to their non‐stressed counterparts, stressed monkeys exhibited a lower 22‐hour mean RQ (0.66 ± 0.03 vs. 0.78 ± 0.05; p&lt;0.05) as well as that during the day (0.69 ± 0.04 vs. 0.81 ± 0.03; p&lt;0.05), dark (0.63 ± 0.02 vs. 0.77 ± 0.07; p&lt;0.05) and morning (0.67 ± 0.03 vs. 0.77 ± 0.07; p&lt;0.05) periods. Moreover, stressed monkeys had a greater EE during the morning period (4.1 ± 0.6 vs. 3.5 ± 0.3 kcal/kg; p&lt;0.05) when compared to their non‐stressed counterparts. Finally, energy intake was reduced in the stressed (7.0 ± 8.5) compared to non‐stressed (27.0 ± 12.2) monkeys.ConclusionBesides the low energy intake, the EMTAC enabled the detection of abnormal metabolic changes associated with the apparent stress of long term SCH.

Low Respiratory Quotients in chow-fed Male Bonnet Macaque Monkeys as a potential indicator of Metabolic Stress due to single cage housing

Background: There is lack of knowledge about specific metabolic changes associated with the stress of long term single cage housing (SCH) of previously indoor group housed male bonnet monkeys (Macaca radiata). Therefore, it is hypothesized that long term SCH will alter the normal metabolic profile of previously indoor group housed male bonnet monkeys. Methods: After two months of indoor SCH, each formally indoor grouped housed male bonnet monkey was placed in the primate Enhanced Metabolic Testing Activity Chamber for 22-hour continuous measurements of energy expenditure (kcal/kg/min) and intake (kcal/kg), along with the respiratory quotient (RQ; VCO2/VO2). For analysis, male bonnet monkeys were divided into two groups, metabolically “stressed” and “non-stressed”, based on 22-hour energy intake being below 13, and above 23 kcal/kg, respectively. Furthermore, the 22-hour metabolic test was divided into an eight-hour day, twelve-hour dark and two-hour morning periods, respectively. Differences (p<0.05) were determined by independent t-tests (SPSS v. 13). Results: Energy intake of the “stressed” monkeys was (p<0.05) lower (4.1 ± 5.6 kcal/kg) in comparison to the “non-stressed” group (27.0 ± 10.5). Furthermore, mean 22-hour RQ was lower (p<0.05) in the “stressed” monkeys (0.68 ± 0.05) in comparison to their “non-stressed” counterparts (0.75 ± 0.08). Finally, compared to their “nonstressed” counterparts, mean RQ’s were lower (p<0.05) for the “stressed” group during both the dark (0.74 ± SD 0.09 vs. 0.65 ± SD 0.05) and morning (0.75 ± 0.08 vs. 0.67 ± 0.05) periods. Conclusions: Two-months of indoor SCH were associated with low RQ’s. This could have implications in regards to results obtained for various drug and physiological studies utilizing monkeys subjected to SCH.

Comparative Evaluation of Testosterone Release and its Derivatives in Adult Male Monkeys

The present study was undertaken to compare the release of testosterone and its derivatives in adult male bonnet monkeys by different routes. Testosterone and its derivatives such as T.propionate, T.enanthate, T.undecanoate, T.busiclate and 7 -Methyl 19-nortestosterone (MENT) were administered via different routes that includes intramuscular, Alzet pump and Silastic tubing. It was observed that 5 ng/ml testosterone concentration was maintained up to 45 days with esters like enanthate, undecanoate or buciclate when given via Alzet pump, whereas with Silastic implants, the testosterone concentration was maintained at 5 ng/ml up to 105 days in the enanthate group, 112 days in the undecanoate group and 133 days in the buciclate group. The results of the study clearly establish the efficacy of delivery by Silastic tubing, which maintained high concentration of testosterone buciclate even on Day 49 compared to 18 days by Alzet pumps or only for 13 days by intramuscular route.

Affiliative relationships and reciprocity among adult male bonnet macaques (Macaca radiata) at Arunachala Hill, India

In captivity, male bonnet macaques (Macaca radiata) frequently express "friendship" toward one another, including affiliative behavior such as huddling, grooming, coalitionary support, and sitting in close proximity. The purpose of this study was to determine whether wild adult male bonnet macaques also express "friendship" by investigating whether or not (1) adult male bonnet macaques have affiliative social relationships with other males, (2) the strength of social relationships varies among dyads, (3) there is time-matched reciprocity in allogrooming among dyads, and if so, whether the level of reciprocity occurs within a bout of grooming, a day, or over 2 months (the limit of this study), and (4) a correlation exists between the strength of social relationships and dominance ranks among adult males. Focal samples totaling 150 hr on all seven adult males in one study group were conducted to record both agonistic and affiliative interactions. Agonistic interactions were used to construct a dominance hierarchy, whereas affiliative interactions (sitting in proximity to within 1 m with and without grooming) were used to quantify the existence and strength of social bonds within dyads. Results show that adult male bonnet macaques had differentiated affiliative relationships with other males in their group. There was little reciprocity of grooming within a bout of grooming or within a day, but greater reciprocity over the study period of 2 months. There was no correlation between dominance ranking distance and the strength of affiliative relationship within dyads; however, within dyads lower-ranking males groomed higher-ranking males more than vice versa. This study suggests that friendships in male bonnet macaques are characterized not by immediate tit-for-tat reciprocal altruism, but by reciprocity over a longer time span, and that affiliative social relationships may be less constrained by agonistic relationships than is the case in more despotic species of macaques.

Early-life stress, corpus callosum development, hippocampal volumetrics, and anxious behavior in male nonhuman primates

Male bonnet monkeys ( Macaca radiata) were subjected to the variable foraging demand (VFD) early stress paradigm as infants, MRI scans were completed an average of 4 years later, and behavioral assessments of anxiety and ex-vivo corpus callosum (CC) measurements were made when animals were fully matured. VFD rearing was associated with smaller CC size, CC measurements were found to correlate with fearful behavior in adulthood, and ex-vivo CC assessments showed high consistency with earlier MRI measures. Region of interest (ROI) hippocampus and whole brain voxel-based morphometry assessments were also completed and VFD rearing was associated with reduced hippocampus and inferior and middle temporal gyri volumes. The animals were also characterized according to serotonin transporter genotype (5-HTTLPR), and the effect of genotype on imaging parameters was explored. The current findings highlight the importance of future research to better understand the effects of stress on brain development in multiple regions, including the corpus callosum, hippocampus, and other regions involved in emotion processing. Nonhuman primates provide a powerful model to unravel the mechanisms by which early stress and genetic makeup interact to produce long-term changes in brain development, stress reactivity, and risk for psychiatric disorders.

Early-life stress and neurometabolites of the hippocampus

We tested the hypothesis that early life stress would persistently compromise neuronal viability of the hippocampus of the grown nonhuman primate. Neuronal viability was assessed through ascertainment of N-acetyl aspartate (NAA)–an amino acid considered reflective of neuronal density/functional integrity–using in vivo proton magnetic resonance spectroscopic imaging (MRSI). The subjects reported herein represent a re-analysis of a sample of nineteen adult male bonnet macaques that had been reared in infancy under induced stress by maternal variable foraging demand (VFD) (N=10) or control rearing conditions (N=9). The MRSI spectral readings were recorded using a GE 1.5 Tesla machine under anesthesia. Relative NAA values were derived using NAA as numerator and both choline (Cho) or creatine (Cr) as denominators. Left medial temporal lobe (MTL) NAA/Cho but not NAA/Cr was decreased in VFD subjects versus controls. An MTL NAA/Cho ratio deficit remained significant when controlling for multiple confounding variables. Regression analyses suggested that the NAA/Choline finding was due to independently low left NAA and high left choline. Right MTL showed no rearing effects for NAA, but right NAA was positively related to body mass, irrespective of denominator. The current data indicate that decreased left MTL NAA/Cho may reflect low neuronal viability of the hippocampus following early life stress in VFD-reared versus normally-reared subjects. Given the importance of the hippocampus in stress-mediated toxicity, validation of these data using absolute quantification is suggested and correlative neurohistological studies of hippocampus are warranted.

Early-life stress, corticotropin-releasing factor, and serotonin transporter gene: A pilot study

Recent studies have indicated a gene-by-environment interaction between serotonin transporter gene (5-HTTLPR) polymorphism and childhood abuse on depressive symptoms. In addition, persistent elevation of cerebrospinal fluid (CSF) corticotropin-releasing factor (CRF) concentrations following early-life adversity has been posited to underlie the subsequent development of major depression. This pilot study tested the hypothesis that elevations of juvenile CSF CRF concentrations are, in part, determined by an interaction between polymorphisms of the 5-HTTLPR and early-life stress. Nine juvenile male bonnet macaques (Macaca radiata) had been raised under variable foraging demand (VFD) conditions, a nonhuman primate model of early-life stress, whereas nine subjects were normatively raised under LFD (low foraging demand) conditions. Genotyping revealed that four (44.4%) of the VFD-reared monkeys possessed at least one "s" allele whereas five VFD monkeys were of the l/l genotype. Of the nine LFD subjects, two (22%) had the s/l genotype and seven had the l/l genotype. A "juvenile" CSF sample was obtained at approximately 3 years of age. CSF CRF concentrations were elevated specifically in the VFD "s/s" and "s/l" allele group in comparison to each of the remaining three groups, indicating a gene-by-environment (G×E) interaction.

The role of early life stress in development of the anterior limb of the internal capsule in nonhuman primates

Deep brain stimulation (DBS) of the anterior limb of the internal capsule (ALIC) may be effective in treating depression. Parental verbal abuse has been linked to decreased fractional anisotropy (FA) of white matter and reduced FA correlated with depression and anxiety scores. Utilizing a nonhuman primate model of mood and anxiety disorders following disrupted mother–infant attachment, we examined whether adverse rearing conditions lead to white matter impairment of the ALIC. We examined white matter integrity using Diffusion Tensor Imaging (DTI) on a 3T-MRI. Twenty-one adult male Bonnet macaques participated in this study: 12 were reared under adverse [variable foraging demand (VFD)] conditions whereas 9 were reared under normative conditions. We examined ALIC, posterior limb of the internal capsule (PLIC) and occipital white matter. VFD rearing was associated with significant reductions in FA in the ALIC with no changes evident in the PLIC or occipital cortex white matter. Adverse rearing in monkeys persistently impaired frontal white matter tract integrity, a novel substrate for understanding affective susceptibility.

Effect of constant infusion of gonadotropin releasing hormone (GnRH) agonist Buserelin and antagonist CDB 2085 A using osmotic minipumps on testicular function in adult male bonnet monkey (Macaca radiata): Einfluß einer konstanten Infusion des GnRH-Agonis

The effect of chronic infusion of gonadotropic hormone agonist Buserelin or antagonist CDB 2085 A for 15 weeks via alzet minipumps in adult male bonnet monkeys was studied. Infusion of Buserelin resulted in a decrease in the difference between serum testosterone values at 22.00 hours and 10.00 hours, decrease in responsiveness to injected Buserelin as judged by change in serum testosterone values from pre-injection values and decrease in sperm counts. Infusion of antagonist resulted in a decrease in the difference between serum testosterone values at 22.00 hours and 10.00 hours.

Studies on the male antifertility agent gossypol acetic acid. VI. Effect of gossypol acetic acid on the fertility of bonnet monkey. Macaca radiata.

Gossypol acetic acid (4 mg/day/5 days a week) suspended in Tonoferon tonic was given to male bonnet monkeys, Macaca radiata, by oral route for 3 months. Marked reduction in the sperm count/ejaculate and sperm motility were observed after gossypol treatment; both motility and sperm count/ejaculate returned to the normal level 8-10 weeks after termination of gossypol treatment. The citric acid and fructose levels in the semen of gossypol treated monkeys were not different from those of the controls.

Effect of modulating endogenous prolactin secretion on testosterone production in the adult male bonnet monkey (Macaca radiata):

Adult male bonnet monkeys maintained under regulated light: dark conditions exhibit a nycthemeral surge of testosterone. The present study attempts to determine the effect of administration of drugs that modulate prolactin levels like ergobromocriptine (EBC) and chlorpromazine (CPZ) on testosterone production. The injection of EBC, a known inhibitor of prolactin secretion, could abolish nocturnal testosterone surge irrespective of the drug being given at 8.00 or 17.00 h. Testosterone surge could likewise be inhibited by treating animals with CPZ, a potent stimulator of prolactin secretion. This suggests that alteration in endogenous prolactin level from the normal effects nycthemeral surges of testosterone. The in vivo responsiveness of the testes of monkeys injected either CPZ oder EBC to exogenous LH or LHRH stimulation was tested. While LH could completely override the CPZ induced inhibition in testosterone production it could only partially reverse the EBC effect.