KOSTRZEWA, R. M., J. W. KLARA, J. ROBERTSON AND L. C. WALKER. Studies on the mechanism of sprouting of noradrenergic terminals in rat and mouse cerebellum after neonatal 6-hydroxydopa. BRAIN RES. BULL. 3(5) 525-531, 1978.-The effect of various pharmacologic agents on the noradrenergic innervation of rat cerebellum was observed. It was found that the neurotoxin 6-hydroxydopa (6-OHDOPA), when given to rats at birth, caused a 46% reduction at 5 weeks of age in tyrosine hydroxylase activity in the locus coeruleus, the nucleus of origin for noradrenergic fibers innervating the cerebellum. At the same time, however, both tyrosine hydroxylase activity and NE content were elevated by 50% in the cerebellum. By treating gravid mice with the 6-OHDOPA, which crosses the placental barrier to affect the brains of developing pups, a dissociation has been shown between the elevated cerebellar NE levels and reduced telencephalic NE content. None of the other assorted pharmacological agents-namely amphetamine, metaraminol, apomorphine, α-methyl-ρ-tyrosine, L-dihydroxyphenylalanine and tyramine-when given at birth, caused a permanent elevation in cerebellar NE content. This series of studies suggests that a reduced number of noradrenergic perikarya are providing a greater innervation of the cerebellum than in control rats. Also, alteration of the telencephalic noradrenergic fibers, which are also derived from the locus coeruleus, does not appear to be a necessary event for the initiation of sprouting of noradrenergic fibers in the cerebellum. Because none of the acute-acting pharmacological agents caused a permanent elevation of NE in the cerebellum, it appears that damage, and not mere stimulation or blockade, is a necessary event for initiation of sprouting.

The hypothalamic tuberoinfundibular dopaminergic (TIDA) neurones secrete dopamine, which inhibits prolactin secretion. TIDA neurone numbers are deficient in Ames (df/df) and Snell (dw/dw) dwarf mice, which lack prolactin, growth hormone and thyroid-stimulating hormone. Prolactin therapy initiated before 21 days maintains normal-sized TIDA neurone numbers in df/df mice and, when initiated as early as 7 days, maintains the maximum TIDA neurone numbers observed in dw/dw development, which are decreased compared to those in normal mice. The present study investigated the effect of prolactin dose and species on TIDA neurone development. Snell dwarf and normal mice were treated with saline, 5 μg of ovine prolactin (oPRL), 50 μg of oPRL, or 50 μg of recombinant mouse prolactin (rmPRL) beginning at 3days of age. Brains were analysed at 45 days using catecholamine histofluorescence, and immunohistochemistry for tyrosine hydroxylase or bromodeoxyuridine. Normal mice had greater (P ≤ 0.01) TIDA neurones than dw/dw, regardless of treatment. TIDA neurones in 50 μg oPRL-treated dw/dw mice were greater (P ≤ 0.05) than those in 5 μg oPRL- and rmPRL-treated dw/dw mice, which were greater (P ≤ 0.01) than those in saline-treated dw/dw mice. Fifty microgram oPRL-treated dw/dw mice also had greater (P < 0.01) TIDA neurone numbers than the maximum numbers observed in untreated dw/dw mice development. Among saline, 5 μg oPRL and 50 μg oPRL treatments, but not rmPRL, A14 neurone numbers were higher (P ≤ 0.01) in normal compared to in dw/dw mice. The mechanism of TIDA neurone recruitment was investigated using bromodeoxyuridine (BrdU) treatment at intervals after 21 days. Mice treated with rmPRL, but not oPRL, had increased BrdU incorporation in the periventricular area surrounding the third ventricle and median eminence and in the arcuate nucleus. The data obtained in the present study indicate that oPRL, but not rmPRL, when given at a high enough dose, induces TIDA neurone differentiation in dw/dw mice. This supports neurotrophic effects of prolactin on TIDA neurones in early postnatal development that extends beyond maintenance of the cell population.

Immunohistochemical studies were conducted to assess the subunits of ionotropic and metabotropic glutamate receptor present in the rostral ventrolateral medulla (RVLM) of the rat. Double labeling the medullary sections with polyclonal GluR1, GluR2/3, GluR4, NMDAR1, NMDAR2A/B, mGluR1α, and mGluR2/3 antiserum and monoclonal tyrosine hydroxylase (TH) antiserum revealed nearly all TH immunoreactive (irTH) cells and many TH-negative neurons were immunoreactive to GluR2/3 (irGluR2/3), NMDAR1 (irNMDAR1), and NMDAR2A/B (irNMDAR2A/B). A few RVLM neurons were immunoreactive to GluR1 (irGluR1) and GluR4 (irGluR4), but they were generally TH-negative. Immunoreactivity to mGluR1α (irmGluR1α) appeared to be localized exclusively to fiber-like elements in the RVLM area. Our results show that neurons in the RVLM, including irTH, are endowed mainly with GluR2/3 and NMDAR1 or NMDAR2A/B ionotropic receptor subunits, and that irmGluR1α splice variant appears to be located on nerve fibers ramifying within the RVLM. Moreover, TH-negative neurons in the RVLM appear to bear similar subunits of ionotropic glutamate receptors.

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<p> Schizophrenia is treated with haloperidol, an antipsychotic drug. Although highly effective in treating the positive symptoms of this disease, extrapyramidal side effects also accompany haloperidol treatment, including parkinsonism. Previous investigations revealed that dopamine receptor blockade by haloperidol was not temporally correlated with the appearance of parkinsonian side effects, which begin approximately 3 weeks after haloperidol treatment. In fact, by using tyrosine hydroxylase as a marker for dopamine, TH-immunoreactivity was significantly decreased 5 minutes after haloperidol administration and further downregulation was seen after 10 minutes. Microglial activation has also been implicated in Parkinson's disease models. Haloperidol also induces maximal microglial activation at 5 minutes after administration, with activation increasing by 2 minutes. In this respect, microglial activation may precede TH downregulation, thereby mediating the downregulation. In order to test this possibility, minocycline, a microglial inhibitor, was administered to Sprague-Dawley rats. Minocycline successfully inhibited microglial activation and showed partial protection over TH levels. Caffeine and nicotine have also been implicated as neuroprotective agents in Parkinson's disease. Epidemiological evidence has indicated that both caffeine and nicotine protect against Parkinson's disease. Therefore, caffeine and nicotine were independently tested and found to both prevent TH downregulation and inhibit microglial activation. Overall, microglial activation has been found to correlate with TH downregulation induced by haloperidol. Minocycline, nicotine and caffeine have all been found to inhibit microglial activation, preventing neurotoxicity associated with haloperidol administration. </p> / Thesis / Master of Science (MSc)

Autism is a severe developmental disorder characterized by impairments in reciprocal social interaction and communication, coupled with repetitive stereotypic activities. Evidence from twin and family studies strongly suggest that genetic factors play a significant role in the etiology of autism. The factors involved in the development of autism are also thought to underlie related pervasive developmental disorders (PDD). The affected sib-pair method was used to screen nine autosomal candidate loci in 18 families, each of which have two or more children with autism or a related PDD. Candidate loci were selected on the basis that: (1) the locus is near genetic disorders or chromosomal abnormalities found to co-occur with autism; and/or (2) the gene encodes a protein which has been speculated to play a role in the pathophysiology of autism. Genotypes of the affected children and their parents were determined for the following microsatellite markers which are tightly linked to the candidate genes/regions: 13S118, DRD2, TH, HRAS-1, 22S343, D15S11, GABRB3, 16S291, and DBH. No significant concordance between affected siblings was observed for any of the loci tested. During the study, however, many of the families were found to be uninformative at the dopamine beta hydroxylase (DBH) microsatellite locus. A comparsion of DBH allele frequencies observed in the parents to published British values revealed a significant difference between the two groups (L2=13.16, df=5, p<0.05). Given this finding, and the knowledge that serum DBH activity is largely under the control of DNA sequences in or close to the DBH gene, serum DBH activities were measured in the parents and in an adult control group. Mean serum DBH activity was found to be significantly lower in parents with two autistic/PDD children compared to an adult control group (Student's t=-1.71, df=60, p<0.05). DBH alleles are defined by a polymorphic dinucleotide repeat and the presence or absence of a 19 bp sequence. Upon further analysis the frequency of alleles in which the 19 bp sequence is deleted was found to be significantly increased in the mothers with two autistic/PDD children, compared to both published frequencies (L2=11.99, df=1, p<0.001) and to a Canadian control group (L2=6.96, df=1, p<0.01). Subsequent investigation revealed that deletion of the 19 bp sequence is associated with lower mean serum DBH enzyme activity (nondeletion homozygotes 44.5±28.6 iu/L; heterozygotes 30.4±16.0 iu/L; and deletion homozygotes 20.5±15.3 iu/L; F=5.45, df=59, p<0.01). Based on these findings it is proposed that lowered maternal serum DBH activity provides a uterine environment which, in conjunction with genotypic susceptiblity of a fetus, results in autism or a related PDD. / Thesis / Master of Science (MS)

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