Sensitization to morphine induced by viral-mediated gene transfer

Repeated administration of morphine sensitizes animals to the stimulant and rewarding properties of the drug. It also selectively increases expression of GluR1 (an AMPA glutamate receptor subunit) in the ventral tegmental area, a midbrain region implicated in morphine action. By viral-mediated gene transfer, a causal relation is shown between these behavioral and biochemical adaptations: Morphine's stimulant and rewarding properties are intensified after microinjections of a viral vector expressing GluR1 into the ventral tegmental area. These results confirm the importance of AMPA receptors in morphine action and demonstrate specific locomotor and motivational adaptations resulting from altered expression of a single localized gene product.

Chronic morphine induces visible changes in the morphology of mesolimbic dopamine neurons

The mesolimbic dopamine system, which arises in the ventral tegmental area (VTA), is an important neural substrate for opiate reinforcement and addiction. Chronic exposure to opiates is known to produce biochemical adaptations in this brain region. We now show that these adaptations are associated with structural changes in VTA dopamine neurons. Individual VTA neurons in paraformaldehyde-fixed brain sections from control or morphine-treated rats were injected with the fluorescent dye Lucifer yellow. The identity of the injected cells as dopaminergic or nondopaminergic was determined by immunohistochemical labeling of the sections for tyrosine hydroxylase. Chronic morphine treatment resulted in a mean approximately 25% reduction in the area and perimeter of VTA dopamine neurons. This reduction in cell size was prevented by concomitant treatment of rats with naltrexone, an opioid receptor antagonist, as well as by intra-VTA infusion of brain-derived neurotrophic factor. In contrast, chronic morphine treatment did not alter the size of nondopaminergic neurons in the VTA, nor did it affect the total number of dopaminergic neurons in this brain region. The results of these studies provide direct evidence for structural alterations in VTA dopamine neurons as a consequence of chronic opiate exposure, which could contribute to changes in mesolimbic dopamine function associated with addiction.

Cystic meningiomas in 2 dogs

Two dogs with signs of forebrain disease had hypodense lesions on computed tomography evaluation. Magnetic resonance imaging of the first dog showed a hypointense lesion on the T1-weighted scan and a hyperintense lesion on T2-weighted scanning. At surgery, both dogs had a primary cystic intracranial lesion, and the abnormal tissue adjacent to the cyst had histological features of meningioma. Each dog underwent whole brain irradiation after surgery, and 1 dog lived for 3 years after treatment. While uncommon, meningioma should be considered as a differential diagnosis in dogs with cystic intracranial lesions.

Regulation of CREB expression: in vivo evidence for a functional role in morphine action in the nucleus accumbens

Previous work has shown that chronic opiate administration regulates protein components of the cAMP signaling pathway, specifically in the nucleus accumbens (NAc), a brain region implicated in the reinforcing properties of opiates, and that such adaptations may contribute to changes in reinforcement mechanisms that characterize opiate addiction. In the present study, we examined a possible role for the transcription factor cAMP response element-binding protein (CREB) in mediating these long-term effects of opiates in the NAc. Chronic, but not acute, morphine administration was found to decrease levels of CREB immunoreactivity in the NAc, an effect not seen in other brain regions studied. The functional significance of this CREB down-regulation was then investigated by the use of an anti-sense oligonucleotide strategy that produces a specific and sustained decrease in CREB levels in the NAc, without detectable toxicity. It was found that the antisense oligonucleotide-induced reduction in CREB levels mimicked the effect of morphine on certain, but not all, cAMP pathway proteins in this brain region, whereas a large number of other signal transduction proteins tested were unaffected by this treatment. Our results support a role for CREB in autoregulation of the cAMP pathway in the nervous system, as well as in mediating some of the effects of morphine on this signaling pathway in the NAc.

Adenovirus-based p53 gene therapy in ovarian cancer

Mutations of the p53 tumor suppressor gene are the most common molecular genetic abnormality to be described in ovarian cancer. To determine the feasibility of mutant p53 as a molecular target for gene therapy in ovarian cancer, we constructed an adenovirus vector containing the wild-type p53 gene. The ability of this adenovirus construct (Ad-CMV-p53) to express p53 protein was examined by Western blot analysis in the H358 lung cancer cell line, which has a homozygous deletion of the p53 gene. The ability of the adenovirus vector system to infect ovarian cancer cells was tested using an adenovirus containing the beta-galactosidase reporter gene under the control of the CMV promoter (Ad-CMV-beta gal). The ovarian cancer cell line 2774, which contains an Arg273His p53 mutation, was infected with Ad-CMV-beta gal, and the infected cells were assayed for beta-galactosidase activity after 24 hr. To test the ability of wild-type p53 to inhibit cell growth, the 2774 cell line was infected with Ad-CMV-p53 or Ad-CMV-beta gal, and the effect of these agents on the growth of 2774 cells was determined using an in vitro growth inhibition assay. Western blot analysis of lysates from H358 cells infected with Ad-CMV-p53 showed expression of wild-type p53 protein. When 2774 cells were infected with Ad-CMV-beta gal at a multiplicity of infection (m.o.i.) of 10 PFU/cell, > 90% of cells showed beta-galactosidase activity, demonstrating that these cells are capable of efficient infection by the adenovirus vector. Growth of 2774 cells infected with Ad-CMV-p53 was inhibited by > 90% compared to noninfected cells. The ability of the adenovirus vector to mediate high-level expression of infected genes and the inhibitory effect of Ad-CMV-p53 on the 2774 cell line suggests that the Ad-CMV-p53 could be further developed into a therapeutic agent for ovarian cancer.

Feline spinal lymphosarcoma: a retrospective evaluation of 23 cats

A retrospective study of pathologically confirmed cases of feline spinal lymphosarcoma (FSL) admitted to the Colleges of Veterinary Medicine at the University of Georgia and North Carolina State University from 1973 to 1988 was conducted. Two hundred fourteen cases of feline lymphosarcoma were diagnosed histopathologically; involvement of the central nervous system (CNS) was identified in 26 (12.1%). Twenty-three of these tumors involved the spinal cord, and 22 of the 23 were solitary. A predilection for the thoracic and lumbar vertebral canal was noted. Most cats with spinal disease were young, with mean and median ages of 43 and 24 months, respectively; 67 cats were 36 months of age or younger. In most cases, affected cats had acute neurological deterioration after an initial insidious course. Extraneural abnormalities were not consistently present. Neoplastic lymphocytes diagnostic of FSL were identified on cerebrospinal fluid (CSF) analysis in 6 of 17 cats evaluated. Sixteen of 17 cats evaluated had serologically positive test results for feline leukemia virus (FeLV) p27 antigen, and all cats tested for feline immunodeficiency virus (FIV) antibodies had negative test results.

Medical management of recurrent seizures in dogs and cats

The problem of recurrent seizures is a common and challenging one in veterinary medical practice. The pathophysiology and pharmacologic suppression of focal seizure activity have been studied extensively in basic research settings, yet little is known of the genesis, modulation, and termination of generalized seizures, the most common form of seizures noted to occur in companion animals. Knowledge concerning the pharmacokinetic fate of anticonvulsant drugs currently used in veterinary medicine is adequate, though prospective clinical studies of the efficacy of these drugs in the treatment of various types of seizures are lacking. This study will review the available literature regarding the pharmacology, use, and side effects of anticonvulsant drugs currently available for control of recurrent seizures in companion animals. Alternative anticonvulsant drugs will also be described.