Potentiation of amygdala AMPA receptor activity selectively promotes escalated alcohol self-administration in a CaMKII-dependent manner

Growing evidence indicates that drugs of abuse gain control over the individual by usurping glutamate-linked mechanisms of neuroplasticity in reward-related brain regions. Accordingly, we have shown that glutamate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) activity in the amygdala is required for the positive reinforcing effects of alcohol, which underlie the initial stages of addiction. It is unknown, however, if enhanced AMPAR activity in the amygdala facilitates alcohol self-administration, which is a kernel premise of glutamate hypotheses of addiction. Here, we show that low-dose alcohol (0.6 g/kg/30 minutes) self-administration increases phosphorylation (activation) of AMPAR subtype GluA1 S831 (pGluA1 S831) in the central amygdala (CeA), basolateral amygdala and nucleus accumbens core (AcbC) of selectively bred alcohol-preferring P-rats as compared with behavior-matched (non-drug) sucrose controls. The functional role of enhanced AMPAR activity was assessed via site-specific infusion of the AMPAR positive modulator, aniracetam, in the CeA and AcbC prior to alcohol self-administration. Intra-CeA aniracetam increased alcohol-reinforced but not sucrose-reinforced responding and was ineffective following intra-AcbC infusion. Because GluA1 S831 is a Ca2+/calmodulin-dependent protein kinase II (CaMKII) substrate, we sought to determine if AMPAR regulation of enhanced alcohol self-administration is dependent on CaMKII activity. Intra-CeA infusion of the cell-permeable CaMKII peptide inhibitor myristolated autocamtide-2-related inhibitory peptide (m-AIP) dose-dependently reduced alcohol self-administration. A subthreshold dose of m-AIP also blocked the aniracetam-induced escalation of alcohol self-administration, demonstrating that AMPAR-mediated potentiation of alcohol reinforcement requires CaMKII activity in the amygdala. Enhanced activity of plasticity-linked AMPAR-CaMKII signaling in the amygdala may promote escalated alcohol use via increased positive reinforcement during the initial stages of addiction.

Activation of mGluR2/3 following stress hormone exposure restores sensitivity to alcohol in rats

Sensitivity to the interoceptive effects of alcohol is blunted following a period of exposure to the stress hormone corticosterone (CORT), an effect that is suggested to be related, in part, to glutamatergic neuroadaptations. Group II metabotropic glutamate receptors (subtypes 2 and 3; mGluR2/3) modulate several drug- and alcohol-related behaviors, including the interoceptive (discriminative stimulus) effects of alcohol. Therefore, we sought to determine if manipulation of mGluR2/3 would restore sensitivity to the interoceptive effects of alcohol following CORT exposure. Using a two-lever drug discrimination task, male Long-Evans rats were trained to discriminate alcohol (1 g/kg, intragastric [IG]) vs. water. First, the effect of mGluR2/3 antagonism on the discriminative stimulus effects of alcohol was determined using LY341495 (0.3-3.0 mg/kg; intraperitoneal [IP]). Next, the effects of mGluR2/3 antagonism and activation were assessed in discrimination-trained animals exposed to CORT (300 μg/mL) in the home cage drinking water or water only, for 7 days. Following CORT exposure, decreased sensitivity to alcohol (1 g/kg) was observed. Pretreatment with the mGluR2/3 agonist LY379268 (1.0-3.0 mg/kg; IP), but not the mGluR2/3 antagonist (0.3-1.0 mg/kg; IP), restored sensitivity to alcohol. Additionally, in water controls, mGluR2/3 antagonism and mGluR2/3 activation disrupted expression of the discriminative stimulus effects of alcohol. Together, these findings suggest that blunted sensitivity to the interoceptive effects of alcohol following an episode of heightened stress hormone levels may be due to adaptations in mGluR2/3-related systems. The ability of mGluR2/3 activation to restore sensitivity to alcohol under these conditions lends further support for the importance of these receptors under stress-related conditions.

Transient increase in alcohol self-administration following a period of chronic exposure to corticosterone

Stressful life events and chronic stressors have been associated with escalations in alcohol drinking. Stress exposure leads to the secretion of glucocorticoids (cortisol in the human; corticosterone (CORT) in the rodent). To model a period of heightened elevations in CORT, the present work assessed the effects of chronic exposure to the stress hormone CORT on alcohol self-administration. Male Long Evans rats were trained to self-administer a sweetened alcohol solution (2% sucrose/15% alcohol) resulting in moderate levels of daily alcohol intake (0.5-0.7 g/kg). Following stable baseline operant self-administration, rats received CORT in the drinking water for 7 days. A transient increase in alcohol self-administration was observed on the first self-administration session following CORT exposure, and behavior returned to control levels by the second session. Control experiments determined that this increase in alcohol self-administration was specific to alcohol, unrelated to general motor activation, and functionally dissociated from decreased CORT levels at the time of testing. These results indicate that repeated exposure to heightened levels of stress hormone (e.g., as may be experienced during stressful episodes) has the potential to lead to exacerbated alcohol intake in low to moderate drinkers. Given that maladaptive drinking patterns, such as escalated alcohol drinking following stressful episodes, have the potential to put an individual at risk for future drinking disorders, utilization of this model will be important for examination of neuroadaptations that occur as a consequence of CORT exposure in order to better understand escalated drinking following stressful episodes in nondependent individuals.

Enhanced AMPA receptor activity increases operant alcohol self-administration and cue-induced reinstatement

Long-term alcohol exposure produces neuroadaptations that contribute to the progression of alcohol abuse disorders. Chronic alcohol consumption results in strengthened excitatory neurotransmission and increased α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPA) receptor signaling in animal models. However, the mechanistic role of enhanced AMPA receptor activity in alcohol-reinforcement and alcohol-seeking behavior remains unclear. This study examined the role of enhanced AMPA receptor function using the selective positive allosteric modulator, aniracetam, in modulating operant alcohol self-administration and cue-induced reinstatement. Male alcohol-preferring (P-) rats, trained to self-administer alcohol (15%, v/v) versus water were pre-treated with aniracetam to assess effects on maintenance of alcohol self-administration. To determine reinforcer specificity, P-rats were trained to self-administer sucrose (0.8%, w/v) versus water, and effects of aniracetam were tested. The role of aniracetam in modulating relapse of alcohol-seeking was assessed using a response contingent cue-induced reinstatement procedure in P-rats trained to self-administer 15% alcohol. Aniracetam pre-treatment significantly increased alcohol-reinforced responses relative to vehicle treatment. This increase was not attributed to aniracetam-induced hyperactivity as aniracetam pre-treatment did not alter locomotor activity. AMPA receptor involvement was confirmed because 6,7-dinitroquinoxaline-2,3-dione (AMPA receptor antagonist) blocked the aniracetam-induced increase in alcohol self-administration. Aniracetam did not alter sucrose-reinforced responses in sucrose-trained P-rats, suggesting that enhanced AMPA receptor activity is selective in modulating the reinforcing function of alcohol. Finally, aniracetam pre-treatment potentiated cue-induced reinstatement of alcohol-seeking behavior versus vehicle-treated P-rats. These data suggest that enhanced glutamate activity at AMPA receptors may be key in facilitating alcohol consumption and seeking behavior, which could ultimately contribute to the development of alcohol abuse disorders.

Assessment of the interoceptive effects of alcohol in rats using short-term training procedures

In the present study, we sought to determine whether the interoceptive effects of alcohol (1 g/kg, IG) could be assessed using a Pavlovian discrimination method, in which the alcohol drug state sets the occasion for which an environmental stimulus (e.g., light) will be followed by a sucrose reward. This procedure takes advantage of a naturally occurring behavior (i.e., food-seeking) which can be trained rapidly prior to the initiation of discrimination training. Given that the interoceptive effects of alcohol are routinely assessed using operant drug discrimination methods, another group of rats was trained using standard two-lever operant drug discrimination procedures in an effort to compare the Pavlovian procedure to a known behavioral benchmark. The results from this work show that, in addition to operant discrimination procedures, a Pavlovian discrimination task can be used to evaluate the interoceptive effects of alcohol. In addition to the brief behavioral sucrose access training (3 days) required prior to the initiation of the Pavlovian discrimination, the alcohol discrimination was acquired relatively rapidly (i.e., 8 training sessions), shortening the overall duration of the experiment. These features of the Pavlovian procedure make it a valuable method by which to assess the interoceptive effects of alcohol if a short experimental time frame is required, such as assessing the interoceptive effects of alcohol during a brief developmental window (e.g., adolescence) or determining the effects of a pretreatment (i.e., chronic stress, chronic drug pretreatment) on the acquisition of the alcohol discrimination. As such, this initial characterization confirms the feasibility of using this Pavlovian discrimination training method as an additional tool by which to assess the interoceptive effects of alcohol, as there may be experimental situations that necessitate short term discrimination training.

The effects of repeated corticosterone exposure on the interoceptive effects of alcohol in rats

RATIONALE AND OBJECTIVE

Repeated and/or heightened elevations in glucocorticoids (e.g., repeated stress) can promote escalated drug-taking behaviors and induce compromised HPA axis function. Given that interoceptive/subjective drug cues are a fundamental factor in drug-taking behavior, we sought to determine the effects of exposure to repeated elevations in the glucocorticoid corticosterone (CORT) on the interoceptive effects of alcohol in rats using drug discrimination techniques.

METHODS

Male Long Evans rats trained to discriminate alcohol (1 g/kg, IG) vs. water were exposed to CORT (300 μg/ml) in the home cage drinking water for 7 days. The interoceptive effects of experimenter- and self-administered alcohol were assessed and HPA axis function was determined.

RESULTS

The interoceptive effects of experimenter- and self-administered alcohol were blunted following CORT. Control experiments determined that this decreased sensitivity was unrelated to discrimination performance impairments or decreased CORT levels at the time of testing and was dependent on repeated CORT exposure. Susceptibility to compromised HPA axis function following CORT exposure was suggested by an altered pattern of CORT secretion and blunted CORT response following injection of the synthetic glucocorticoid dexamethasone.

CONCLUSIONS

These findings present a possible behavioral mechanism for escalated alcohol drinking during episodes of heightened elevations in glucocorticoids (e.g., stress). That is, during these episodes, individuals may consume more alcohol to achieve the desired interoceptive effects. Understanding these behavioral mechanisms may lead to a better understanding of factors that promote alcoholism and alcohol abuse in at risk populations.

Intra-amygdala inhibition of ERK(1/2) potentiates the discriminative stimulus effects of alcohol

Extracellular signal-regulated kinase (ERK(1/2)) has been implicated in modulating drug seeking behavior and is a target of alcohol and other drugs of abuse. Given that the discriminative stimulus (subjective/interoceptive) effects of drugs are determinants of abuse liability and can influence drug seeking behavior, we examined the role of ERK(1/2) in modulating the discriminative stimulus effects of alcohol. Using drug discrimination procedures, rats were trained to discriminate a moderate intragastric (IG) alcohol dose (1g/kg) versus water (IG). Following an alcohol (1g/kg) discrimination session phosphorylated ERK(1/2) (pERK(1/2)) immunoreactivity (IR) was significantly elevated in the amygdala, but not the nucleus accumbens. Therefore, we hypothesized that intra-amygdala inhibition of ERK(1/2) would disrupt expression of the discriminative stimulus effects of alcohol. However, intra-amygdala or accumbens administration of the MEK/ERK(1/2) inhibitor U0126 (1 and 3μg) had no effect on the discriminative stimulus effects of the training dose of alcohol (1g/kg). Contrary to our hypothesis, intra-amygdala infusion of U0126 (3μg) potentiated the discriminative stimulus effects of a low alcohol dose (0.5g/kg) and had no effect following nucleus accumbens infusion. Importantly, site-specific inhibition of pERK(1/2) in each brain region was confirmed. Therefore, the increase in pERK(1/2) IR in the amygdala following systemic alcohol administration may be reflective of the widespread effects of alcohol on the brain (activation/inhibition of brain circuits), whereas the site specific microinjection studies confirmed functional involvement of intra-amygdala ERK(1/2). These findings show that activity of the ERK signaling pathway in the amygdala can influence the discriminative stimulus effects of alcohol.

Activation of group II metabotropic glutamate receptors inhibits the discriminative stimulus effects of alcohol via selective activity within the amygdala

Metabotropic glutamate receptor subtypes (mGlu2/3) regulate a variety of alcohol-associated behaviors, including alcohol reinforcement, and relapse-like behavior. To date, the role of mGlu2/3 receptors in modulating the discriminative stimulus effects of alcohol has not been examined. Given that the discriminative stimulus effects of drugs are determinants of abuse liability and can influence drug seeking, we examined the contributions of mGlu2/3 receptors in modulating the discriminative stimulus effects of alcohol. In male Long-Evans rats trained to discriminate between alcohol (1 g/kg, IG) and water, the mGlu2/3 agonist LY379268 (0.3-10 mg/kg) did not produce alcohol-like stimulus effects. However, pretreatment with LY379268 (1 and 3 mg/kg; in combination with alcohol) inhibited the stimulus effects of alcohol (1 g/kg). Systemic LY379268 (3 mg/kg, i.p.) was associated with increases in neuronal activity within the amygdala, but not the nucleus accumbens, as assessed by c-Fos immunoreactivity. Intra-amygdala activation of mGlu2/3 receptors by LY379268 (6 μg) inhibited the discriminative stimulus effects of alcohol, without altering response rate. In contrast, intra-accumbens LY379268 (3 μg) profoundly reduced response rate; however, at lower LY379268 doses (0.3, 1 μg), the discriminative stimulus effects of alcohol and response rate were not altered. These data suggest that amygdala mGlu2/3 receptors have a functional role in modulating the discriminative stimulus properties of alcohol and demonstrate differential motor sensitivity to activation of mGlu2/3 receptors in the amygdala and the accumbens. Understanding the neuronal mechanisms that underlie the discriminative stimulus effects of alcohol may prove to be important for future development of pharmacotherapies for treating alcoholism.

Anatomy of the lumbosacral spinal cord in rabbits

This study provides an accurate, anatomical description of the rabbit's lumbosacral spinal cord. Following humane euthanasia, 64 rabbits were radiographed and dissected. The number of thoracic (T) and lumbar (L) vertebrae was 12T/7L in 43.8%, 13T/6L in 32.8%, and 13T/7L in 23.4% in the 64 rabbits studied. The 13th ribs were rudimentary, asymmetric, or both in 15 animals. The spinal cord terminated within the second sacral vertebra (S2) in 79.3%, within the first sacral vertebra (S1) in 19.0%, and within the third sacral vertebra (S3) in 1.7% of the sample. Spinal nerve contributions to the femoral, obturator, sciatic, and pudendal nerves were determined. Formulas to predict the termination of the cord relative to the vertebral column were established. Age, weight, sex, and method of preparation did not show a significant correlation with the length of the spinal cord.

Parapagus conjoined twin Holstein calf

BACKGROUND

Conjoined twins with a doubling of all cranial structures, having two vertebral columns along their entire body length yet with a single pelvis, have not been described in the literature. The cause of conjoined twinning is incompletely understood; however, two main theories (fission and fusion) have been proposed and disputed.

METHODS

A dicephalus, tetrabrachius (parapagus) conjoined twin Holstein heifer calf was studied.

RESULTS

Two normal heads were present on two necks. The twins were fused in the thoracic region. There were four forelimbs and an abnormal orientation of ribs. Two separate vertebral columns along the length of the animal ended with two tails. There was a single pelvis, and only two hindlimbs were present. The musculature of the medial forelimbs was complete but abnormally positioned. Some medial structures, caudal to the thorax, failed to develop in these twins. There were two hearts, each one supplying one half of the body. The cranial vasculature was doubled and normal. Caudally there were two aortas, each supplying the respective half of the twin. The right caudal vena cava drained all caudal parts of the body while the left caudal vena cava drained only the liver. There were two sets of lungs. Each twin had a separate esophagus that entered a separate stomach. The right abomasum (fourth stomach chamber) was herniated through the diaphragm into the thoracic cavity. The two duodenums from each stomach fused distal to the pyloric sphincters. Caudal to this point of fusion, all structures of the digestive and urogenital systems were single. The calf had a single anus and vulva.

CONCLUSIONS

The anatomical findings in this twin suggest a fission event followed by fusion of parallel embryonic axes.

Agonadal presumptive XX/XY leukochimeric pig

BACKGROUND

XX/XY chimeric pigs are uncommon and their reproductive anatomy is variable and unpredictable.

METHOD

A piglet was identified by its enlarged vulva as a possible intersex. Venous blood was collected at 1.5 and 9 months for karyotyping and determination of testosterone and estrone sulphate concentrations. At 1 year euthanasia was performed. The reproductive tract was carefully dissected and examined histologically.

RESULTS

As the animal matured the vulva did not develop relative to the size of the animal. Lymphocyte cultures indicated a 70% XX/30% XY chimera. The reproductive tract consisted of a strand of tissue enveloped by fascia. Histological study revealed presumptive Wolffian derivatives, coiled bilateral ducts along the tract, and a Müllerian derivative, a medially located duct in the caudal third of the tract. No gonads were found. Plasma levels of estrone sulfate and testosterone were negligible.

CONCLUSIONS

In utero exposure to exogenous androgens from a male co-twin or weak endogenous adrenal androgens may account for the enlarged vulva at birth and retention of the androgen dependent Wolffian duct primordia. An atesticular state is supported by retention of the Müllerian duct primordia and the negligible peripheral sex steroids.

Prospective clinicopathologic studies of schizophrenia: accrual and assessment of patients

OBJECTIVE

The purpose of this study was to characterize the neuropsychiatric profile of elderly patients with schizophrenia and establish a patient registry for prospective ante-mortem and post-mortem studies.

METHOD

Medical records of all chronically institutionalized patients in eight state hospitals who were over the age of 65 and had a chart diagnosis of schizophrenia (N = 528) were reviewed. Of the potential subjects, 192 were excluded because of clinical histories inconsistent with a diagnosis of schizophrenia, 56 because of insufficient information to establish a psychiatric diagnosis, and 122 because of family members' refusal to give consent for autopsy in the event of death. To date, 81 of the remaining 158 patients have undergone neuropsychiatric evaluation with standard assessment instruments.

RESULTS

Mini-Mental State scores of the 81 patients indicated severe dementia, and Functional Assessment Scale scores showed that patients required assistance with activities of daily living. All patients were rated as severely ill on the Brief Psychiatric Rating Scale. Ratings on the Scale for the Assessment of Negative Symptoms and the Scale for the Assessment of Positive Symptoms indicated a predominance of negative symptoms over positive. Of 30 patients who have died to date, research autopsies have been conducted on 26.

CONCLUSIONS

Establishing a well characterized, prospective patient registry for clinicopathologic studies of schizophrenia is feasible but labor intensive. Diagnosis of schizophrenia with a high degree of confidence can be achieved by means of detailed chart review and assessment of current neuropsychiatric functioning with standard rating instruments. These data provide a basis for correlations of clinicopathologic factors.

Conjoined twin piglets with duplicated cranial and caudal axes

BACKGROUND

Twins with doubling of the cranial and caudal poles, yet having a single thorax, are rare.

METHODS

One set of diprosopus, dipygus porcine conjoined twins was studied.

RESULTS

In addition to the conjoining anomaly, these twins also exhibited ambiguous internal reproductive features. The twins had two snouts, three eyes, a single thorax, and were duplicated from the umbilicus caudally. Radiography indicated a single vertebral column in the cervical region. The vertebral columns were separate caudally from this point. There was a total of six limbs--one pair of forelimbs and two pairs of hindlimbs. Many medial structures failed to develop in these twins. Medial cranial nerves V-XII were absent or displaced although apparently normal laterally. The medial palates were present but shortened, whereas the medial mandibular rami had folded back on themselves rostrally to form a midline mass between the two chins. Each twin had only one lateral kidney and one lateral testis. Medial scrotal sacs were present but devoid of a testis. There was a midline, "uterine"-like structure which crossed between the twins. However, histological analysis of this structure revealed it to be dysplastic testicular tissue.

CONCLUSIONS

The relationship between the abnormal reproductive features in these twins and the conjoining is unclear. The anatomy of these twins, in addition to the literature reviewed, illustrates the internal anatomical heterogeneity of grossly similar conjoined twins. A review of the literature also suggests that conjoined twinning may be more common in swine than was previously suspected.

Characterization of a translocation and its impact on fertility in the pig

A chromosome anomaly originally detected in two intersex pigs and previously reported as a Robertsonian translocation was characterized, and its transmission pattern was assessed by analyzing the progeny and immediate relatives of a sow. Cytogenetic investigations on four phenotypically normal relatives of the intersexes, including a sow, showed that the rearrangement was a reciprocal translocation involving the X chromosome and an autosome. Giemsa-banding and reverse-banding techniques indicated that the break in the X chromosome may have occurred in the terminal segment of the short arm (Xp) and that in the autosome in the proximal segment of the acrocentric chromosome 14 (14q). Reverse-banding techniques also revealed that the normal X is the late-replicating X in female translocation carriers. Centromere banding revealed an intercalary band on the long arm of the submetacentric chromosome representing the altered X in translocation carriers. The translocation was designated as rcp (X;14) (p+;q-). Chromosome analysis on 45 of 72 live offspring of the carrier sow showed a 20:25 distribution of carriers to normal piglets, with a carrier to normal ratio of 5:13 among females and 15:12 among male piglets, indicating an overall reduction of females (18) compared with males (27). Male carriers from one litter at sexual maturity showed hypoplastic testes and no spermatozoa in their ejaculates or fluid aspirates from the cauda epididymis. Their seminiferous tubules were narrow, spermatogenesis was impaired, and pyknotic and giant nuclei were abundant in the germinal epithelium. Meiotic preparations showed no stage beyond pachytene, suggesting that the absence of spermatozoa in the ejaculates may be due to the arrest of cells at the pachytene stage.

Prevalence and types of birth defects in Ontario swine determined by mail survey

Preweaning mortality in piglets constitutes a major loss to the swine industry. Congenital defects account for a small but significant proportion of these losses. To implement appropriate strategies to reduce such losses, it is necessary to identify the specific causes and their relative importance. Consequently, a mail survey of swine production in Ontario was carried out to determine the prevalence and types of birth defects. Statistical comparisons of the prevalence of overall defects were made between accurate and estimate records, breeds (cross vs. purebred), size of operation (number of sows) and geographic location. The mean litter size of 11 pigs born per sow was not significantly different for those with accurate versus estimate records, but the difference in the prevalence of defective pigs (live and dead) was significant (accurate 3.1% vs. estimate 4.1%). Splayleg (spraddleleg) was the most common defect. The next four defects for both groups were belly rupture, other rupture, ridglings and other, but not in the same ranking. Purebred and small farm operations (< 25 sows) had a significantly higher prevalence of birth defects for estimated data only. Geographic location had no effect. Further work is required to determine whether recording prevalence of birth defects in Ontario swine will provide a useful monitor of environmental stress. The study provides a baseline for the prevalence and type of defects in Ontario swine.

Comparison of androst-16-ene steroid levels determined by a colorimetric assay with boar taint estimated by a trained sensory panel

A group of 17 intact male pigs and 3 gilts ranging in weight from 96 to 260 kg was selected for sensory evaluation of boar taint in loin chops. Samples were evaluated by 10 trained judges using a 10-cm graphic scale for rating off-aroma, off-flavor, pork flavor, softness, tenderness, juiciness, and residual tissue. In addition, a fry test for taint was conducted by four experienced testers on fat samples from all animals. Androst-16-ene steroid levels were measured in salivary gland and fat. Two versions of a colorimetric assay for the androst-16-ene steroids were used, a complete version, in which cholesterol was removed from the tissue extracts using a digitonin-Sepharose affinity column, and a simplified version, which does not include this step. The off-aroma and off-flavor sensory scores showed a good correlation with the androst-16-ene levels in fat and salivary glands and high correlations were obtained between the androst-16-ene steroid levels in fat and salivary glands. The levels of the androst-16-ene steroids in the salivary gland were highly correlated with the levels of estrogen in the blood and to a lesser extent with the levels of testosterone in the blood. Similar correlation coefficients were obtained between salivary gland androst-16-ene steroid levels measured using either the complete or simplified versions of the colorimetric assay and the off-aroma and off-flavor sensory scores. The results of the fry test were variable and no statistically significant correlations were obtained between the fry test results and the off-aroma and off-flavor sensory scores from the trained sensory panel.(ABSTRACT TRUNCATED AT 250 WORDS)

An inherited connective tissue disease in the horse

The hyperextensible, fragile skin of two related horses was compared with the skin of eight normal horses. Skin sections were examined by light microscopy and transmission electron microscopy. The deep dermal layer of the dorsal abdomen was much thinner in the affected horses, and contained bundles of collagen fibers which were more loosely packed. Within individual fibers, the fibrils were frequently curved and nonparallel rather than straight and parallel. Both of the affected animals had a greater range of fibril diameters than a normal horse. They had some unusually thick fibrils with very irregular outlines in cross-sections, not observed in the normal animal. Other skin samples were subjected to acetic acid extraction, pepsin digestion, amino acid analysis and polyacrylamide gel electrophoresis. In the skin of the two affected horses, the proportion of total extracted collagen which was acid-soluble was twice as high as in two normal horses. Collagen types I and III were present in similar proportions in normal and affected horses, and the collagen chains were of normal molecular weights. The disorder resembles the group described by Minor (Minor RR: Am J Pathol 98: 226, 1980) as 'dominant collagen packing defect I' which has been reported in dogs, mink, and cats, and which shares features with Ehlers Danlos Syndrome I, II, and III in man. The pedigree data available for these horses suggest an autosomal recessive mutation, but are also consistent with autosomal dominant inheritance.

An unusual manifestation of holoprosencephaly in a pig

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Two-headed, two-necked conjoined twin calf with partial duplication of thoracoabdominal structures: role of blastocyst hatching

Gross anatomical analysis of a derodidymic monosomic stillborn male calf from an embryo transfer recipient was carried out. Two normal heads were present on two necks which were fused at the shoulders. Although the ribs were abnormal in shape and number, there was one trunk and four legs. The vertebrae were double and partially fused from the thoracic region to the sacrum, which was singular and normal. In the thoracic region there was a single vertebral canal that contained two incompletely fused spinal cords which shared common meninges. In the lumbar region there was a spina bifida. The medial neck musculature was variously fused. Two esophagi entered one enlarged rumen and the liver and gallbladder had extra lobes. Two sets of lungs occupied three pleural cavities and also part of the pericardial cavity. Two hearts were joined by a common cavernous venous sinous. The vasculature cranial to the heart reflected the doubling. The vasculature caudally was singular. The calf was uniscrotal and ipsilaterally cryptorchid. Our results are consistent with the hypothesis that atypical "hatching," that is, emergence of the blastocyst from the zona pellucida, may cause anomalous twinning.

Clinical and anatomical observations of a two-headed lamb

The clinical and anatomical features of a live-born diprosopic lamb are described. There are no complete anatomical analyses of two-faced lambs in the literature despite the frequency of conjoined twinning in sheep. The lamb had two heads fused in the occipital region. Each head had two eyes. The pinnae of the medial ears were fused. Caudal to the neck the lamb appeared grossly normal. The lamb was unable to raise its heads or stand. Both heads showed synchronous sucking motions and cranial reflexes were present. Nystagmus, strabismus, and limb incoordination were present. The respiratory and heart rates were elevated. There was a grade IV murmur over the left heart base and a palpable thrill on the left side. Each head possessed a normal nasopharynx, oropharynx, and tongue. There was a singular laryngopharnyx and esophagus although the hyoid apparatus was partially duplicated. The cranial and cervical musculature reflected the head duplications. The aortic trunk emerged from the right ventricle just to the right of the conus arteriosus. A ventricular septal defect, patent foramen ovale, and ductus arteriosus were present along with malformed atrioventricular valves. Brainstem fusion began at the cranial medulla oblongata between cranial nerves IX and XII. The cerebella were separate but small. The ventromedial structures from each medulla oblongata were compressed into an extraneous midline remnant of tissue which extended caudally to the level of T2. The clinical signs therefore reflected the anatomical anomalies. A possible etiology for this diprosopus might be the presence early in development of an excessively large block of chordamesoderm. This would allow for the formation of two head folds and hence two "heads."

Intersexes in swine: a problem in descriptive anatomy

Accurate anatomical descriptions of ten intersex pigs were compiled through dissection and histological examination in order to identify specific groups of reproductive anomalies. Six different anatomical phenotypes were identified: four varieties of male pseudohermaphrodite, one type of female pseudohermaphrodite and one type of true hermaphrodite. The intersex phenomenon is complicated by the number of distinct anatomical phenotypes represented broadly by the term hermaphrodite. Therefore, accurate anatomical descriptions and precise terminology are prerequisites to defining the etiology of hermaphroditism and defining the modes of inheritance.

The development of chick spinal cord in tissue culture. III. Neuronal precursor cells in culture

On culturing fragments of neural tube of Hamilton and Hamburger (H & H) Stage 10 chick embryos, large multipolar neurons developed. The aim of this investigation was to determine whether these neurons in culture developed from dividing neuronal precursor cells, from postmitotic precursor cells, or both. Of the neurons formed during the 20 d of culturing in the presence of [3H]thymidine, 26% were unlabeled, indicating that they originated from cells that were already postmitotic at the time of explantation. By labeling cells of the neural tube in vivo and determining the total number of cells in the neural tube, we estimated that the neural tube of chick embryos of H & H Stage 10 contained approximately 1000 (3.3%) postmitotic cells. By estimating the total number of neurons that formed in 20-d cultures and the percentage of labeled and unlabeled neurons, we concluded that the postmitotic neuronal precursor cells survived well in cultures and proceeded on their predetermined path of differentiation. By considering the number of neurons found in the spinal cord in vivo and the number of labeled neurons found in cultures, we concluded that only a relatively small fraction of the dividing neuronal precursor cells entered the postmitotic stages of differentiation and formed neurons in cultures. The majority of cells that did this, entered the postmitotic stage of differentiation during the first 5 d in culture.

Morphology of a two-headed piglet

A live-born, one-day-old diprosopic piglet was presented to the Ontario Veterinary College. The piglet had a normal body with two heads, joined in the occipital region. There were two complete snouts, four eyes and three ears. The lower jaws were immobile because of overlapping mandibular rami. Although there was only one vertebral column, the bodies of the vertebrae, but not the neural arches, were doubled from the axis to T8. There was one thyroid gland and one larynx and hyoid apparatus. The two tongues were joined at their base just rostral to the single epiglottis. The palate was completely split in the right head but only partially split in the left. the cranial nerves were normal and doubled except for IX, X and XI. The brains were fused at the pon-medulla junction. An anomalous midline tag of neural tissue resembling remnants of the medical halves of two nervous systems extended form this point to the level of T8. Possible developmental mechanisms and rates of incidence are discussed.

The development of chick spinal cord in tissue culture. II. Cultures of whole chick embryos

By using whole-chick-embryo cultures followed by fragment cultures of spinal-cord primordia, it was possible to reproduce in vitro the whole process of neuronal development beginning with its initiation and continuing up to and including the maturation of neurons. Normal whole embryos were developed to Hamilton-Hamburger stages 17 and 18 by growing embryos from the primitive streak stage on large (28-mm) glass rings. The advantage of whole-embryo cultures is that development can be staged accurately, which is especially important during the early stages when morphogenesis progresses very rapidly. By using such accurately staged embryos and tritiated thymidine, we have determined that some postmitotic neuronal precursor cells appear in chick embryos as early as Hamburger-Hamilton stages 4 and 5, i.e. the definitive streak stages before the neural tube has formed.

The development of chick spinal cord in tissue culture. I. Fragment cultures from embryos of various developmental stages

Explants from neural tube and spinal cord of chick embryos at developmental stages 8 through 36 were cultured on collagen-coated cover glasses for 21 days. The cultures of neural tube at stages 10 to 14 contained many neuronal precursor cells which gave rise to mature neurons. This was verified by cumulative labeling of cultures with tritiated thymidine. Explants from spinal cords of stages 26 and 27 contained fewer precursor cells, and at stage 36, only 7% of mature neurons were labeled. Regardless of the stage of development at which explants were made (stages 8 through 36), all cultures had a similar appearance after 21 days, indicating that cells from explants taken from earlier developmental stages (before neurons were formed) "caught up" with the explants from later developmental stages, which already had formed neurons at the time of explantation.

Effect of osmotic pressure on neurogenesis in cultures of chich embryo spinal cords

The osmotic pressure of the medium in stoppered, roller tube cultures increased by an average of 17 +/- 6 mOsM per kg of water during 3 days of incubation at 37 degrees C irrespective of the initial osmolality (280 to 340 mOsM) of the medium. The increase was apparently due to evaporation of water from the medium into the gas phase of the roller tube. This observation led us to study the effect of osmotic pressure on neuronal differentiation in cultures of chick embryo spinal cords. Spinal cords were excised from stage 16 to 19 (2.5 to 3 days of incubation) or stage 36 (10 days) chick embryos and cultured as fragments on collagen-coated cover slips in roller tubes at 37 degrees C for 21 days. The medium was adjusted to 283 +/- 3,300 +/- 3,323 +/- 3, or 342 +/- 3 mOsM per kg with saturated choline chloride solution or distilled water. The results indicate that the nature of the neuronal differentiation in vitro was not altered by the osmolality of the medium. The proportion of cultures containing neurons was influenced by osmolality. In the 300 +/- 3 mOsM medium, 75% of all the stage 36 cultures initiated contained neurons, and 52% of all the stage 16 to 19 cultures initiated contained neurons. In the other media the proportion of neuron-containing cultures was lower. Two conclusions were drawn. Neurogenesis in cultures of embryonic chick spinal cord fragments is sensitive to an increase in the initial osmotic pressure of the medium as small as 20 mOsM above the optimal 300 mOsM. As a result of the 17 mOsM increase which always occurred in the culture medium between feedings, the optimum osmolality for neuronal development is in fact a range, from 300 to 317 mOsM.

Rates of oxygen uptake by embryonic anterior horn tissue isolated at various developmental stages

Neuroepithelial cells of the presumptive spinal cord (stage 11) consume oxygen, albeit at a low rate. As neurons differentiate in the presumptive motor horns the rate of oxygen consumption increases to approximately 70 mumoles/g wet wt/hr by stage 26. It is suggested that the rate of oxygen consumption per unit volume of neuron then remains constant as subsequent development ensues but since the neurons become more widely spaced the oxygen consumption per unit volume of anterior horn tissue decreases.