Nitrous Oxide as an Emerging Cause of Subacute Combined Degeneration and Polyneuropathy: A Two-Case Report.

Recreational use of nitrous oxide (N2O), commonly known as laughing gas, has increased in the last few years, bringing an increase in the number of reported cases of toxicity due to this gas. Subacute combined degeneration (SCD) of the spinal cord is the most frequently reported neurological disorder due to the use of N2O, as well as polyneuropathy and even psychiatric symptoms. All of these disorders are consequences of a functional deficit of vitamin B12. We are reporting the cases of two patients with a history of N2O abusive use presenting to the emergency department with progressive symptoms of paresthesia, ascending symmetric paraparesis, and gait ataxia, emulating the clinical characteristics of Guillain-Barré Syndrome (GBS). In both cases, magnetic resonance imaging (MRI) showed findings compatible with transverse myelitis of the cervical spinal cord, and electrodiagnosis studies reported the presence of polyneuropathy with a mixed mechanism. All these findings together pointed to the presence of myeloneuropathy due to a vitamin B12 deficit induced by the prolonged use of N2O. Symptoms improved gradually with vitamin B12 supplementation and abstinence from N2O. It is important to acknowledge the clinical characteristics of complications due to neurotoxicity induced by N2O. Such complications are potentially reversible if they are treated appropriately and quickly. Considering the increase in N2O abuse, it should be considered a probable cause when treating patients with myelopathy and/or neuropathy of an unusual etiology.

Toxoplasma gondii infection lower anxiety as measured in the plus-maze and social interaction tests in rats A behavioral analysis.

It has been suggested that the parasite Toxoplasma gondii reduces the fear of rodents toward their feline predators, which may lead to an augmented rate of predation and multiplication of the parasite through an increased number of life cycles. To investigate whether T. gondii infection induces selective effects on behavior associated with anxiety, Wistar rats were inoculated i.p. with several doses of T. gondii tachyzoites and tested in two animal tests of anxiety. In the third week following inoculation, rats infected with 100 and 1000 tachyzoites increased plus-maze open arm exploration in a dose-related manner. However, no effect was detected in either social interaction levels or motor activity measures. In the seventh week after inoculation, rats infected with 100 and 1000 tachyzoites showed increased open arm exploration and social investigation without change on any motor activity measures. However, rats infected with a higher dose (1500 tachyzoites) showed a drop in locomotion. These data support the hypothesis that T. gondii impairs mechanism of warning as a function of reduced anxiety. The pattern of brain colonization by the parasite and the host immune response suggests that the predominant invasion to limbic areas works as a natural anxiolytic mechanism.

Distribution of mucopolysaccharides and glycoproteins in the articular discs of temporomandibular joints in human fetuses.

AIMS: To evaluate the distribution of mucopolysaccharides and glycoproteins in the articular discs of temporomandibular joints (TMJs) in human fetuses at different stages of development in order to test the hypothesis that the development and histological maturation of the articular disc has already begun by the 12th week of gestation. METHODS: Eighteen human fetuses at gestational ages 12, 14, and 16 weeks were used (6 fetuses of each age). Sections (6 microm wide) of the articular discs were stained with trichromic stain for collagen fibers, Mayer's mucicarmine for mucopolysaccharides, and Schiff's periodic acid reaction for glycoproteins. The densities of the stained zones were measured by means of Image J software. The nonparametric Kruskal-Wallis test was used to evaluate the differences among stained zones in the 3 fetus groups. RESULTS: TMJ tissues of four of the six 12-week-old fetuses were stained positive for collagen fibers, mucopolysaccharides, and glycoproteins. In these fetuses the stain was localized to the articular posterior area and was denser in that area than in the middle and anterior areas. The stained areas in the 14-week-old fetuses were distributed throughout the articular discs, with isolated clear unstained areas. The stained areas of all the articular discs of the 16-week-old fetuses were more compact than those of the 12-and 14-week-old fetuses. In all the fetuses examined, the collagen fibers along the articular disc had a wavy appearance. The fossa of the temporal bone was observed in all the fetuses as a straight structure that was similar in the 3 fetus groups. The densities (mean +/- SD) of the stained zones were 38.36% +/- 3.39%, 59.5% +/- 1.56%, and 94.04% +/- 2.04% for 12, 14, and 16 weeks of gestation, respectively; these densities were significantly different (chi2 = 15.16; df = 2, P < .001). CONCLUSION: This study indicates that mucopolysaccharides and glycoproteins as well as collagen fibers are present at 12, 14, and 16 weeks of gestation. This suggests that the histological maturation of the articular disc has already begun at the 12th week and is complete by the 16th week of gestation.

Tonic and phasic alteration in amygdala 5-HT, glutamate and GABA transmission after prefrontal cortex damage in rats.

The relationship between the ventromedial prefrontal cortex and the amygdala during the presentation of an unconditioned fear stimulus was assessed. Rats underwent bilateral ibotenic acid or vehicle administration into the ventromedial prefrontal cortex. Five weeks later, the behavior as well as the neurochemical changes in the amygdala was evaluated before and after a brief cat presentation. Lesioned animal freezing behavior increased 10 times when compared to controls. In the right basolateral amygdala, basal concentrations of 5-HT, 5-HIAA, glutamate and serine were elevated but basal level of GABA was diminished in lesioned animals relative to controls. Sham but not lesioned animals increased 5-HT and decreased GABA and serine levels after cat presentation. Phasic changes in glutamate were not detected either in lesioned or shams but the difference in amygdala glutamate between lesioned and shams persisted after cat presentation. These data show that increased serotonin and glutamate tone and decreased gabaergic tone in the amygdala correlate to elevated fear and anxiety after prefrontal cortex ibotenic acid lesion. The lesion also seems to produce a failure of adaptive changes in neurotransmitter systems revealing lost of control of the ventromedial prefrontal cortex over the amygdala in frightening situations.