Evaluation of nigrostriatal dopaminergic function in adult +/+ and +/- BDNF mutant mice.

Deletion of a single copy of the BDNF gene has been shown to affect the nigrostriatal dopaminergic system of young adult BDNF mice. In the present report we evaluated various indices of nigrostriatal dopaminergic function between 9-month-old wild-type (+/+) and heterozygous (+/-) BDNF mutant mice. Performance in a sensorimotor beam walking task was significantly decreased in +/- mice as indicated by increased times required to traverse both a wide (21 mm) and narrow (6 mm) beam. No differences in spontaneous locomotor behavior were observed between the +/+ and +/- mice. Amphetamine-stimulated (5 mg/kg) locomotor behavior was increased to a greater degree in the +/- mice, with the number of movements performed by these mice being significantly greater than their +/+ controls. Corpus striatal dopamine concentrations were significantly greater in the +/- BDNF mice. The absence of any significant differences for dopamine concentrations within the hypothalamus and olfactory bulb of these mice, as well as an absence of any difference in striatal norepinephrine concentrations, suggested a relative specificity of these effects to the corpus striatum. Both the +/- and +/+ mice showed similar reductions in striatal dopamine concentrations in response to a neurotoxic regimen of methamphetamine (20 mg/kg). Collectively these data show increased levels of striatal dopamine concentrations associated with altered behavioral responses involving the nigrostriatal dopaminergic system within the heterozygous BDNF mutant mice.

Inactivation of one copy of the mouse neurotrophin-3 gene induces cardiac sympathetic deficits.

Whether two copies of the neurotrophin-3 (NT3) gene are necessary for proper development of cardiac sympathetic innervation was investigated in mice carrying a targeted inactivation of the NT3 gene. Heterozygous (+/-) and null (-/-) mutant mice had fewer stellate ganglion neurons than did wild-type (+/+) mice at postnatal day 0 (P0 or birth), and this deficit was maintained between adult (P60) +/- and +/+ mice. The sympathetic innervation of the heart matured postnatally in +/+ and +/- mice. Tyrosine hydroxylase (TH)-positive axons were restricted largely to the epicardium at P0, were concentrated around large blood vessels in the myocardium at P21, and were present among cardiac myocytes at P60. Cardiac norepinephrine (NE) concentrations paralleled the growth of the sympathetic axons into the heart. NE concentrations were equivalent among +/+, +/-, and -/- mice at birth, but differences between +/- and +/+ mice increased with age. Adult +/- mice also exhibited lower resting heart rates and sympathetic tonus than +/+ mice. Thus deletion of one copy of the NT3 gene translates into anatomical, biochemical, and functional deficits in cardiac sympathetic innervation of postnatal mice, thereby indicating a gene-dosage effect for the NT3 gene.

Alterations in nigrostriatal dopaminergic function within BDNF mutant mice.

The influence of brain-derived neurotrophic factor (BDNF) upon the nigrostriatal dopaminergic system was evaluated in weanling and adult mice carrying a targeted inactivated BDNF gene. Regional specificity of this BDNF mutation was assessed by assaying catecholamine concentrations within the corpus striatum, hypothalamus, and olfactory bulbs. In weanling mice dopamine, but not norepinephrine, concentrations within the corpus striatum of homozygous mutant (-/-) mice were significantly reduced with levels being 54% that of the wild-type controls (+/+) and 49% that of the heterozygous mutant (+/-) mice. While no differences were obtained among the three genotypes for hypothalamic dopamine, norepinephrine concentrations of -/- mice were significantly lower, being 62% of +/+ mice and 49% of +/- mice. The dopamine concentrations of -/- mice within the olfactory bulb were significantly reduced (69%) compared to the +/-, but not +/+ mice. Olfactory bulb norepinephrine concentrations showed a statistically significant difference among each of the three conditions with minimal levels in -/- mice (62% of +/+ and 45% of +/-). In the adults, catecholamine concentrations were measured only in +/+ and +/- mice since -/- mice do not typically survive past 21 days. Dopamine, but not norepinephrine, concentrations within the corpus striatum were significantly increased (116%) in +/- compared to +/+ mice. No other statistically significant differences were obtained in catecholamine concentrations within the hypothalamus or olfactory bulb in these adult mice. These results show that homozygous BDNF mutations produce severe depletions within the nigrostriatal dopaminergic system and substantial reductions of norepinephrine within the hypothalamus and olfactory bulb. Interestingly, maximal catecholamine concentrations for all areas sampled at both ages were observed in the +/- mice. These latter findings may indicate some subtle changes in catecholamine functions resulting from a heterozygous BDNF mutation.

Afferent-inherent regulation of myosin heavy chain isoforms in rat muscle spindles.

Whether afferents exert their morphogenetic influence on spindles through release of trophic factors at intrafusal fiber junctions or via participation in proprioceptive pathways which modulate the motor activity to muscles was investigated by comparing myosin heavy chain (MHC) expression in intrafusal fibers after ablation of afferents (deafferentation, or DA) to the extensor digitorum longus (EDL) of adult rats or after ablation of the corresponding central processes of afferents to the spinal cord (central-process ablation, or CPA). DA and CPA elicited an exaggerated pedal plantarflexion, and hypertrophy of the EDL concomitant with atrophy of the soleus in the affected hindlimb. Frequencies and patterns of expression of seven MHCs expressed by intrafusal fibers in CPA muscles were indistinguishable from normal rats. However, frequencies and patterns of expression of several MHCs were abnormal following DA. Thus factors transported anterogradely from afferents to intrafusal fibers may regulate MHC expression in intrafusal fibers.

Fourier transform spectroscopic imaging using an infrared focal-plane array detector.

A powerful new mid-infrared spectroscopic chemical imaging technique combining step-scan Fourier transform Michelson interferometry with indium antimonide focal-plane array (FPA) image detection is described. The coupling of an infrared focal-plane array detector to an interferometer provides an instrumental multiplex/multichannel advantage. Specifically, the multiple detector elements enable spectra at all pixels to be collected simultaneously, while the interferometer portion of the system allows all the spectral frequencies to be measured concurrently. With this method of mid-infrared spectroscopic imaging, the fidelity of the generated spectral images is limited only by the number of pixels on the FPA detector, and only several seconds of starting time is required for spectral image acquisition. This novel, high-definition technique represents the future of infrared chemical imaging analysis, a new discipline within the chemical and material sciences, which combines the capability of spectroscopy for molecular analysis with the power of visualization. In particular, chemical imaging is broadly applicable for noninvasive, molecular characterization of heterogeneous materials, since all solid-state materials exhibit chemical nonuniformity that exists either by design or by development during the course of material preparation or fabrication. Imaging, employing Raman and infrared spectroscopy, allows the precise characterization of the chemical composition, domain structure, and chemical architecture of a variety of substances. This information is often crucial to a wide range of activities, extending from the fabrication of new materials to a basic understanding of biological samples. In this study, step-scan imaging principles, instrument design details, and infrared chemical imaging results are presented. Since the prospect of performing high-resolution and high-definition mid-infrared chemical imaging very rapidly has been achieved with the step-scan approach, the implications for the chemical analysis of materials are many and varied.