Alterations in red blood cell parameters, plasma amino acids, total cholesterol and fatty acids in Standardbred horses undergoing fitness training

Maintenance of metabolic homeostasis is vital to optimise the supply of nutrients to support exercise and facilitate recovery and repair processes in horses. This study assessed the effects of exercise on resting plasma homeostasis in horses upon initiation of a training program to attain fitness in preparation for competitive harness racing. Four Standardbred horses (three males and one female) that had not been in work for at least 6 months were assessed prior to the commencement of the training program and then progressively on a weekly basis for 8 weeks. Resting plasma samples were collected in the early morning prior to exercise training and feeding. Samples were analysed for amino acid composition, cholesterol, palmitic acid and stearic acid on a weekly basis, and red blood cell counts and haemoglobin were analysed at weeks 0, 4 and 8. The red cell counts and levels of haemoglobin increased progressively over the training period (P<0.05). Specific amino acids in the plasma displayed temporal variations during the training period. Glycine was the most abundant amino acid in resting horse plasma and together with serine was reduced throughout the first half of the training period, eventually returning to initial levels at weeks 7 and 8 (P<0.05). A number of amino acids were noted to increase in concentration throughout the 8 week training period including ornithine, histidine and hydroxyproline (P<0.05). Cholesterol fell to substantially lower levels after 8 weeks of exercise (P<0.05). Palmitic acid showed three ‘peaks’ of elevated concentrations in plasma (P<0.05) following the initiation of exercise and then again at the transitions into harder fast work sessions. Stearic acid was relatively constant throughout the exercise period. Adjustments in the plasma composition of these key metabolites were consistent with supporting the increased metabolic demands associated with the higher levels of exercise training.

Sweat facilitated losses of amino acids in Standardbred horses and the application of supplementation strategies to maintain condition during training

Little is known about the amino acid composition of horse sweat, but significant fluid losses can occur during exercise with the potential to facilitate substantial nutrient losses. Sweat and plasma amino acid compositions for Standardbred horses were assessed to determine losses during a standardised training regime. Two cohorts of horses 2013 (n=5) and 2014 (n=6) were assessed to determine baseline levels of plasma and sweat amino acids. An amino acid supplement designed to counter losses in sweat during exercise was provided after morning exercise daily for 5 weeks (2013, n=5; 2014, n=4). After the supplementation period, blood and sweat samples were collected to assess amino acid composition changes. From baseline assessments of sweat in both cohorts, it was found that serine, glutamic acid, histidine and phenylalanine were present at up to 9 times the corresponding plasma concentrations and aspartic acid at 0-2.2 μmol/l in plasma was measured at 154-262 μmol/l in sweat. In contrast, glutamine, asparagine, methionine and cystine were conserved in the plasma by having lower concentrations in the sweat. The predominant plasma amino acids were glycine, glutamine, alanine, valine, serine, lysine and leucine. As the sweat amino acid profile did not simply reflect plasma composition, it was proposed that mechanisms exist to generate high concentrations of certain amino acids in sweat whilst selectively preventing the loss of others. The estimated amino acid load in 16 l of circulating plasma was 3.8-4.3 g and the calculated loss via sweat during high intensity exercise was 1.6-3.0 g. Following supplementation, total plasma amino acid levels from both cohorts increased from initial levels of 2,293 and 2,044 µmol/l to post-supplementation levels of 2,674 and 2,663 µmol/l respectively (P<0.05). It was concluded that the strategy of providing free amino acids immediately after exercise resulted in raising resting plasma amino acid levels.

Comparative sequence analysis and radiation hybrid mapping of the canine keratin 10 gene

The type I keratin, K10, is expressed in epidermal keratinocytes undergoing terminal differentiation to form the stratum corneum, a barrier essential for life. In order to facilitate the study of keratinization disorders in the dog, the sequence and mapping of KRT10 is reported. The coding region of KRT10 is 1707 bp and is comprised of eight exons. Although the length of KRT10 has been reported to be polymorphic in humans, this was not observed in the eight domestic dog breeds studied, although one wild canid displayed a size difference. The structure and sequence of this gene is highly conserved across mammalian species. Canine K10 had an 86% amino acid identity with the human gene. KRT10 was localized to the on-going canine radiation hybrid map to chromosome 9 in the type I keratin gene cluster.

Polymorphisms in the interleukin 10 gene promoter are associated with susceptibility to aggressive non-Hodgkin's lymphoma

Interleukin-10 (IL-10) is mainly an anti-inflammatory cytokine produced by a number of cells including normal and neoplastic B cells. It has been implicated in autoimmunity, transplantation tolerance and tumourigenesis. Polymorphisms in the IL-10 gene promoter genetically determine inter-individual differences in IL-10 production. The aim of this study was to determine whether polymorphisms in the IL-10 gene promoter play a role in predisposing an individual to lymphoma. We analysed the frequencies of three single base substitutions in the IL-10 promoter in patients with aggressive lymphoma (B-cell DLCL n = 46, other aggressive histologies n = 17), Hodgkin's disease (n = 44) or low/intermediate grade lymphoma (n = 46), compared to healthy controls. The frequency of the low-IL-10 producing AA allele (at position -1082) was significantly higher in patients with aggressive lymphoma compared to controls (p = 0.0344, Odds ratio 1.974, 95% C.I 1.066-3.655). Similarly, the frequency of the low IL-10 producing ATA or the intermediate-IL-10- producing ACC haplotype was significantly higher in patients with aggressive disease compared to controls (p = 0.0255, Odds ratio 1.647, 95% C.I 1.077-2.518). No association was found between IL-10 genotypes and Hodgkin's disease or less aggressive forms of lymphoma. Thus, polymorphisms in the IL-10 gene promoter which are associated with a low IL-10 producing phenotype may influence susceptibility to aggressive forms of lymphoma or may contribute to the pathogenesis of this disease.

Invasive phaeohyphomycosis caused by Curvularia species in a dog

A 2-year-old female Boxer dog was presented with a history of skin lesions that started 1 month after being given oral glucocorticoids for a neurologic problem. Clinically, the animal had focal areas of alopecia with papules and nodules often with ulceration overlain by crusts. Lesions were most common on the dorsum and the lateral aspects of the trunk and extremities. Histologic evaluation revealed pigmented fungal organisms within the lumina of hair follicles and throughout the dermis and subcutis. These organisms were associated with a multinodular, pyogranulomatous luminal folliculitis/furunculosis, dermatitis, and panniculitis. Curvularia sp. was isolated from the cutaneous lesions. The histologic identification of dematiaceous fungal organisms in the hair follicles may explain how phaeohyphomycosis can occur without history of a penetrating injury.

Dose-dependent transformation of cells of human fibroblast cell strain MSU-1.1 by cobalt-60 gamma radiation and characterization of the transformed cells

Cells from an infinite-life-span near-diploid human fibroblast cell strain, MSU-1.1, were transformed after a single exposure to 60Co gamma radiation. The frequency of transformation as measured by the number of induced foci per 10(6) cells was a linear function of dose. Cells from 13 independent foci from gamma-irradiated cell populations and one from a nonirradiated cell population were isolated, clonally expanded and assayed for characteristics of malignantly transformed cells. Eight of the 13 focus-derived cell strains from the irradiated populations formed tumors in athymic mice with latent periods (time required for the tumors to reach 1 cm in diameter) of 4-27 weeks. Of these 8 cell strains, 3 were fully growth factor-independent, formed large colonies (> 120 microm in diameter) in 0.33% agarose at a high frequency (50%), and produced malignant tumors with a mean latency of 6 weeks or less at all sites injected. Four others formed colonies in agarose at a slightly lower frequency, were only partially growth factor-independent, and produced malignant tumors with a longer mean latency (7-18 weeks). The tumor-derived cell lines from these latter 4 cell strains, when tested for growth in agarose, showed markedly enhanced anchorage independence. The eighth tumorigenic focus-derived cell strain was growth factor-independent but could not produce large colonies in agarose. It produced benign tumors (fibromas) with a mean latency of 27 weeks. All 8 tumorigenic focus-derived cell strains had lost the transactivating function of the TP53 (formerly known as p53) gene. However, loss of TP53 activity was not sufficient to cause tumorigenicity since 3 of the 6 nontumorigenic focus-derived cell strains had also lost all TP53 transactivation function. The other 3, which included a cell strain from the unirradiated control, had wild-type TP53 alleles and did not form tumors. These latter results support the hypothesis that loss of TP53 transactivating function plays a role in focus formation, but does not directly cause tumorigenicity. This is in agreement with studies that demonstrate that the loss of TP53 transactivation facilitates the other changes required for tumorigenicity.

Bovine hereditary zinc deficiency: lethal trait A 46

Bovine hereditary zinc deficiency, also referred to as Adema disease, is an autosomal recessive disorder which results in inadequate amounts of zinc being absorbed from the gastrointestinal tract and leads to a number of clinical abnormalities. Using semen from a homozygous affected bull and obligate heterozygote cows in embryo transfer studies, 7 offspring were obtained. These included 5 affected calves and 1 heterozygous carrier; the seventh calf died within 48 hours of birth undiagnosed. One unaffected, unrelated bull calf was raised as a control. All the calves were raised and maintained under similar management conditions designed to minimize secondary complications that would obscure the clinical and biochemical observations of a zinc deficient state. The first clinical manifestation of zinc deficiency was diarrhea, followed by skin lesions, poliosis, and a decreased ability to sustain a suckle reflex. Trace mineral analysis of plasma blood samples revealed that plasma zinc concentrations of all the calves were normal at birth; however, they gradually declined in affected calves over the course of 3-8 weeks postpartum to below 0.5 ppm. Biochemical analysis of serum samples showed alkaline phosphatase activity consistently paralleled changes in the plasma zinc concentrations. The oral administration of zinc acetate caused a reversal of all clinical, biochemical, and histologic abnormalities in affected calves. The study of these affected calves allows further insight into the biological role of zinc as well as provides an animal model for the continued investigation of the human homologue acrodermatitis enteropathica.

Adenosine triphosphate-magnesium chloride in radiation injury

Although adenosine triphosphate-magnesium chloride (ATP-MgCl2) has demonstrated cytoprotective effects in a variety of adverse pathophysiologic conditions, its ability to alter radiation injury is unknown. The purpose of this study, therefore, was to assess the effects of ATP-MgCl2 on colorectal radiation injury after preoperative pelvic radiotherapy. Mixed-breed pigs (n = 36) received 4250 cGy preoperative external-beam pelvic radiotherapy (350 cGy fractions three times per week for 4 weeks). During radiotherapy, animals were randomly assigned to one of three treatment groups: (1) intravenous infusions of normal saline during radiotherapy, (2) intravenous ATP-MgCl2 (30 mumol/kg) during radiotherapy, or (3) intravenous ATP-MgCl2 (60 mumol/kg) during each radiotherapy session. After completion of radiotherapy and a 4-week rest period, animals underwent colorectal resection by either the two-layer hand-sewn (n = 18) or stapled end-to-end anastomosis technique (n = 18). Laser Doppler velocimetric readings were obtained to assess mural colonic blood flow after completion of anastomosis. A second laparotomy on postoperative day 5 or 11 was done to examine the following anastomotic parameters: (1) repeat laser Doppler velocimetry, (2) gross inflammatory scoring, (3) bursting pressure, (4) preoperative barium enema to identify leak or stenosis, (5) analysis of anastomotic hydroxyproline content, and (6) incidence of cutaneous injury in the radiation portals. ATP-MgCl2 administered intravenously at 60 mumol/kg led to (1) diminished colorectal seromuscular ischemia evidenced by laser Doppler velocimetric readings, (2) decreased skin and subcutaneous tissue injury in the treatment portals, (3) significantly decreased perianastomotic inflammatory reaction, and (4) increased early hydroxyproline content. There was no significant difference in the incidence of leakage or stenosis between the study groups, nor was the anastomotic bursting strength significantly different between the treatment groups. Therefore the administration of ATP-MgCl2 (60 mumol/kg) appears to offer significant cytoprotection from preoperative pelvic radiation therapy.

Revisional Surgery for Failed Gastric Restrictive Procedures for Morbid Obesity

As part of the Adelaide Obesity Surgery Study, we have reviewed all patients who have undergone revisional surgery. Of the 31 0 trial patients, 63 (20%) had revisions 1-69 (median 32) months following their original surgery-30% of all 105 gastrogastrostomy (GG) operations, 22% of 106 gastroplasty (GP) procedures, and 9% of 99 gastric bypasses (GB). Failure was due to stomal dilatation, 11% of all trial patients (71% of GG revisions), stomal stenosis, 6% (52% of GP revisions) and staple dehiscence, 4%. There was no mortality and a low hospital morbidity. Long-term success was only 23% (follow-up at least 3 years) and was achieved at considerable expense (3 reversals, 10 further revisions, 44 endoscopic procedures). Revisional surgery was successful in 45% of patients with stomal dilatation or dehiscence but in only 17% with stenosis. Overall, the most successful operation was revision of, or conversion to, gastric bypass (58% success rate), compared with gastroplasty (24%) and gastrogastrostomy (25%). Our long-term results following revisional surgery were disappointing, particularly for stenosis, and most failures followed revision to GG or GP. Roux-en-Y gastric bypass is the procedure of choice when considering revision.

Does a proximal colostomy affect colorectal anastomotic healing?

Fecal diversion has been implicated as an etiologic factor in anastomotic stenosis following colorectal surgery, particularly following the use of circular anastomotic stapling devices. However, experimental confirmation of the effects of fecal diversion on anastomotic healing is virtually nonexistent. The purpose of this study was to serially evaluate colorectal anastomotic healing with proximal colostomy (COL) and without it (CON; control) using two anastomotic techniques in a porcine model. Fifty-two (28 CON; 24 COL) mixed-breed female pigs had colorectal anastomoses using either a two-layer hand-sewn (HS) or an EEA (U.S. Surgical Corporation, Norwalk, CT) circular stapled (CS) technique. Anastomotic blood flow was measured using laser Doppler velocimetry (LDV). At second surgery (5, 11, 60, or 120 days postoperatively), the following data were collected: repeat LDV, gross and microscopic anastomotic inflammatory scores, anastomotic diameter, and bursting pressure. There were no significant differences in anastomotic blood flow (LDV), inflammatory scores, or incidence of leak or stenosis between the CON and COL groups or between anastomotic techniques. Bursting pressure was significantly lower for the COL group at day 11 but not any other postoperative day (POD). Proximal colostomy does not appear to exert adverse effects on colorectal anastomotic healing. The choice of colorectal anastomotic technique should not be influenced by the need for proximal colostomy.

Roseola infantum and other syndromes associated with acute HHV6 infection

Eight cases of acute human herpesvirus type 6 (HHV6) infection in infants were diagnosed serologically by the demonstration of IgM anti-HHV6 (8/8) and a significant change in total anti-HHV6 antibody titre (6/8). Four infants were sufficiently ill to require admission to hospital and further investigations: one with encephalitis and three with gross hepatosplenomegaly, two of whom had evidence of simultaneous infection with another herpes-virus. The remaining four infants had an illness compatible with roseola infantum, although this diagnosis had not been made clinically. Sera from two of those infants with rash had been sent for analysis to exclude rubella because the infants' mothers were pregnant. The other two had received antibiotics when febrile, and the subsequent appearance of the roseola rash had raised the possibility of antibiotic allergy. The data suggest that there are clinical syndromes in addition to roseola infantum associated with the presence of IgM anti-HHV6, in which serological screening for evidence of acute HHV6 infection may be useful.

Intramural pH: a quantitative measurement for predicting colorectal anastomotic healing

Leakage and stenosis are serious complications of gastrointestinal anastomotic surgery that may, in part, be related to local ischemia. The ability to accurately quantitate the degree of gastrointestinal anastomotic ischemia remains a challenging clinical problem. The purpose of this study was to: 1) develop a model of colorectal anastomotic stenosis following local ischemia; 2) compare the accuracy of laser Doppler velocimetry and intramural colonic pH in quantitating critical levels of intestinal anastomotic ischemia; and 3) compare the anastomotic healing process using either a standard two-layer Czerny-Lembert handsewn or EEATM stapled anastomotic technique under ischemic conditions. The studies reported here were performed in two phases. Phase I was the pilot study in which the authors developed a model of colorectal anastomotic ischemia and defined critical levels of ischemia using laser Doppler velocimetry and intramural pH (less than or equal to 200 mV; less than or equal to 7.0, respectively). These parameters were then tested prospectively in Phase II, assessing the effects of anastomotic ischemia on animals kept alive for 5, 11, 21, and 60 days after surgery. Overall there was a 70 percent incidence of anastomotic healing complications in the Phase II trial with laser Doppler velocimetry correctly predicting anastomotic outcome in 70 percent of cases and tissue pH in 93 percent of cases. The results indicate that, although laser Doppler velocimetry and intramural pH measurements provide safe, easy techniques for assessing the effects of ischemia on the colorectal anastomosis, measurement of intramural pH provides an optimal quantitative method for predicting subsequent anastomotic outcome and tissue viability.

Involvement of caudate nucleus, amygdala or reticular formation in neuroleptic and narcotic catalepsy

Local injection of haloperidol into the caudate nucleus produced catalepsy in contrast to the weak effects of morphine injected at the same site. Injection of either haloperidol or morphine into the amygdala did not have any cataleptogenic effect. Both haloperidol and morphine produced catalepsy when injected into the reticular formation. Naloxone injected into the reticular formation completely reversed the catalepsy following intraperitoneal morphine but not haloperidol. Pretreatment with alpha-methyl-p-tyrosine potentiated the effect of haloperidol injected into either the reticular formation or caudate nucleus. Phentolamine but not lignocaine or metergoline, injected into the reticular formation also caused a cataleptic response. The results confirm the caudate nucleus as a site for haloperidol catalepsy and in addition, suggest the reticular formation as a primary site for morphine catalepsy and a secondary site for haloperidol catalepsy; additionally a noradrenergic modulation of catalepsy may occur within this brainstem region.

Long-term haloperidol-treatment of mice: a change in beta-adrenergic receptor responsiveness

Mice administered haloperidol 3 mg/kg/day in their drinking water for 21 days were tested for their locomotor responsiveness to saline or acid vehicle, dl-, l- or d-propranolol, metoprolol, butoxamine or practolol. Haloperidol-treated animals administered saline or acid-vehicle were, in five of six experiments, more active than animals withdrawn from vehicle-treatment. Haloperidol- and vehicle-treated animals responded differently to the non-selective beta-adrenoreceptor antagonists (dl-propranolol and l-propranolol) and selective beta1-adrenoreceptor antagonists (practolol and metoprolol), but not to a selective beta2-adrenoreceptor antagonist (butoxamine). With dl-propranolol (4 mg/kg) the locomotor activity of haloperidol-treated animals was significantly (0.01 less than P less than 0.02) greater than that of the vehicle-treated animals. Similar effects in the same direction were seen with l-propranolol (1 mg/kg, 0.005 less than P less than 0.01), practolol (10 and 100 mg/kg, 0.025 less than P less than 0.05 and 0.01 less than P less than 0.025 respectively) and metoprolol 8 mg/kg, 0.005 less than P less than 0.01). The d-isomer of propranolol which is about 50 times less active as a beta-adrenoreceptor antagonist than the l-isomer, although having equal membrane stabilizing effects, did not differentially affect haloperidol- or vehicle-treated groups. The results suggest that there has been a change in beta 1-adrenoreceptor responsiveness in animals withdrawn from long-term haloperidol treatment.

The hyperkinetic syndrome following long-term haloperidol treatment: involvement of dopamine and noradrenaline

Mice withdrawn for 7 days from a 35-day treatment period with haloperidol (3 mg/kg/day) displayed significantly greater spontaneous locomotor activity (hyperkinesia) than animals withdrawn from the vehicle. The hyperkinesia was antagonized by phenoxybenzamine (an alpha-adrenergic receptor antagonist) and by FLA-63 (a dopamine-beta-hydroxylase inhibitor) but not by haloperidol (a dopamine receptor antagonist). alpha-Methyl tyrosine (a tyrosine hydroxylase inhibitor) was effective in antagonizing the hyperkinesia and this blockade by alpha-methyl tyrosine could be completely reversed by the administration of a low dose of the catecholamine precursor, DOPA. The data suggest that noradrenergic systems are of importance for the manifestation of the hyperkinetic syndrome seen in mice withdrawn from long-term haloperidol treatment.

Further evidence for a change in central alpha-adrenergic receptor sensitivity after withdrawal from long-term haloperidol treatment

Phenoxybenzamine, FLA-63 and alpha-MT produced less locomotor depression in mice withdrawn for 4 days from a 21 day treatment with haloperidol than that produced in vehicle-treated animals. There were no differences between the two groups when challenged with yohimbine or phentolamine. The data support the hypothesis that central alpha-adrenergic receptors had become supersensitive and suggest that the sensitivity changes are restricted to post-synaptic receptors.

The demonstration of a change in responsiveness of mice to physostigmine and atropine after withdrawal from long-term haloperidol pretreatment

Mice, administered haloperidol 3 mg/kg/day, in their drinking water for 21 days, were tested for their responsiveness to cholinergic and anticholinergic drugs 4 days after withdrawal from haloperidol (or vehicle). Haloperidol-treated animals administered methylhyoscine (1 mg/kg i.p.) and various doses of physostigmine (5 to 1215 microgram/kg) displayed significantly less depression of locomotor activity than vehicle-treated animals. Atropine, 5 mg/kg, whilst ineffective in producing locomotor stimulation in vehicle-treated animals, produced marked stimulation in haloperidol-treated animals. Methylatropine (5 mg/kg) did not produce significant stimulation in either group. Dopamine receptor supersensitivity was present in these animals as haloperidol-treated mice, pretreated with alpha-methyltyrosine and reserpine, displayed a significantly greater locomotor response to apomorphine than did vehicle-treated animals. The data support the hypothesis that long-term administration of haloperidol produces an apparent hyposensitivity of central muscarinic receptors.

The effect of apomorphine and clonidine on locomotor activity in mice after long term treatment with haloperidol

1. Mice were given haloperidol (approximately 3 mg.kg-1 day-1) or vehicle for 21 days and then withdrawn from the drug. All tests were performed 4 days after withdrawal. 2. Haloperidol treated mice (premedicated with reserpine plus alpha-methyl-p-tyrosine) displayed an increased locomotor response to apomorphine and to apomorphine plus clonidine, but neither haloperidol- or vehicle-treated animals revealed any stimulant response to clonidine. 3. In mice which had not been pretreated with reserpine plus alpha-methyl-p-tyrosine, clonidine produced a significant stimulation of locomotor activity in animals withdrawn from haloperidol but not in those withdrawn from the vehicle. Phenoxybenzamine blocked the locomotor stimulat difference between these two groups, but did not completely antagonized the stimulant effect of clonidine in mice withdrawn from haloperidol. Pimozide was largely effective in blocking the clonidine-induced stimulation. Co-administration of phenoxybenzamine and pimozide was completely effective in blocking the stimulant effect of clonidine in mice withdrawn from haloperidol. 4. The evidence for a change in catecholamine receptor sensitivity was supported compared to the vehicle-treated animals. 5. The data suggest that there is a change in the functional responsiveness of both adrenergic and dopaminergic receptors after withdrawal from long term haloperidol treatment.

The demonstration of a change in adrenergic receptor sensitivity in the central nervous system of mice after withdrawal from long-term treatment with haloperidol

Mice, administered haloperidol (3 mg/kg/d) in their drinking water for 21 days, displayed, 4 days after cessation of the haloperidol-treatment, marked locomotor stimulation to clonidine (100 or 500 mug/kg) which lasted for about 6 h. 25 mug clonidine/kg was inactive. Premedication with FLA-63 (25 mg/kg) blocked the difference in stimulation after clonidine between the haloperidol- and vehicle-treated animals, but locomotor activity was still present in both groups. Haloperidol-treated animals displayed a supersensitive response to dexamphetamine. The difference in stimulation produced by dexamphetamine in the two groups was completely blocked by phenoxybenzamine (2.5 mg/kg), phentolamine (10 mg/kg), which drugs did not, however, block the locomotor stimulation produced by dexamphetamine in vehicle-treated animals. Pimozide (3 mg/kg) blocked all locomotor stimulation produced by dexamphetamine in both vehicle- and haloperidol-treated groups, while 1 mg/kg completely blocked the dexamphetamine response in vehicle-treated animals but not in haloperidol-treated animals. FLA-63 (25 mg/kg) blocked the difference in response between the haloperidol- and vehicle-treated groups to dexamphetamine, but did not antagonise the stimulation in the vehicle-treated animals. The data suggest that long-term haloperidol treatment leads to the development of "supersensitive" adrenergic receptors in the central nervous system, which, appropriately stimulated, effect an increase in locomotor activity. Moreover, the results indicate that a large component of the supersensitive response to dexamphetamine observed after long-term haloperidol-treatment is due to adrenergic receptor supersensitivity. However, the dopamine receptor (which was shown to be supersensitive to apomorphine) is of fundamental importance because phenoxybenzamine and phentolamine, while blocking the supersensitive response to dexamphetamine, failed to block the response to dexamphetamine in vehicle-treated animals, which was, however, blocked by pimozide.