Neuroscience
-
Comparative Study
Heterogeneity of evoked dopamine overflow within the striatal and striatoamygdaloid regions.
The heterogeneity of evoked dopamine overflow in vivo was examined and compared in striatal and striatoamygdaloid regions of the rat. The characteristics of appearance and disappearance rates and the maximum concentration elicited were determined from overflow curves measured by fast-scan cyclic voltammetry. Overall, the characteristics of evoked dopamine overflow were quite variable in the striatum compared to the relative uniformity of overflow in the basolateral amygdaloid nucleus. ⋯ In contrast, differences in evoked dopamine overflow within the striatoamygdaloid region were sharply defined dorsoventrally and appeared to be region-specific. Dopamine terminal fields in the striatum are not clearly demarcated into the caudate-putamen and nucleus accumbens, but may exist as a continuum. The uptake of dopamine appears to be the distinguishing characteristic for the regulation of extracellular dopamine levels in the striatum and the basolateral amygdaloid nucleus.
-
In order to develop a rodent model displaying a progressive degeneration of the dopamine neurons of the substantia nigra, we bilaterally injected the tracer substance FluoroGold into the terminal field of the nigrostriatal projection, i.e. the striatum. One week later, rats received unilateral injections of 20 micrograms 6-hydroxydopamine into one of the two striatal tracer deposits. Groups of animals were killed one, two, four, eight and 16 weeks later. ⋯ We conclude that injection of 6-hydroxydopamine into the terminal field of nigral dopaminergic neurons causes a progressive degeneration of these cells, starting between one and two weeks after lesion and continuing over eight to 16 weeks. This degeneration is preceded, and accompanied by, cellular atrophy and a partial loss of marker enzyme expression, thus yielding an animal model which mimics the degenerative processes in Parkinson's disease more closely than the animal models available so far. The present model may be helpful in investigating the in vivo effects of putative neuroprotective agents and neurotrophic factors.
-
Changes in chemical sensitivity of peripheral nociceptors following injury or inflammation have been studied in in vitro preparation of the saphenous nerve-hind paw skin from adult rats. Heat hyperalgesia in the hind paw was induced by a prior ultraviolet irradiation and the skin from these animals was investigated five days later. Polymodal nociceptors were quiescent in normal skin but were spontaneously active in the majority of fibres after ultraviolet exposure. ⋯ These data show that polymodal nociceptors change their activity and sensitivity to exogenous chemicals following the induction of peripheral hyperalgesia by ultraviolet irradiation. Specifically, evidence is provided for the expression of opioid sensitivity and inhibition of polymodal nociceptor activity through mu- and kappa-opioid receptors. These observations may account for peripheral antinociceptive actions of opioids during specific states of peripheral hyperalgesia.
-
The anterograde and retrograde transport of wheat germ agglutinin-horseradish peroxidase was used to study the trigeminoperibrachial pathway in the muskrat after injections of tracer into either the medullary dorsal horn or the dorsolateral pons. After injections into the medullary dorsal horn, labeled fibers ascended into the ipsilateral dorsolateral pons via the spinal trigeminal tract, within the neuropil of the trigeminal sensory complex and within the reticular formation adjacent to the spinal trigeminal nucleus. At caudal levels of the ipsilateral peribrachial area, dense terminal-like label distributed in the Kölliker-Fuse nucleus continued into the lateral parabrachial nucleus. ⋯ In the medullary dorsal horn, they were found almost exclusively in laminae I and V. Labeled neurons in lamina I were especially prominent in rostral ventral levels of the medullary dorsal horn. Labeled cells in lamina I were continuous with others found in the displaced band of substantia gelatinosa at the interface of the subnucleus caudalis and subnucleus interpolaris, as well as with those found in the ventral and dorsal paratrigeminal nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)
-
Neurogenesis, migration and maturation of ganglion cells in the posterior pole of chick retina have been studied using embryonic incorporation of [3H]thymidine, immunocytochemistry and retrograde labeling. Unlike previous studies, we have examined the neurogenesis of independently identified ganglion cells that have survived the period of naturally occurring cell death (embryonic days 11-16). Embryos were labeled with [3H]thymidine at different embryonic ages (embryonic days 3, 5 and 7). ⋯ Using immunocytochemistry with an antibody against neuron-specific beta-tubulin and retrograde labeling with the carbocyanine dye DiI we show that ganglion cells begin to differentiate before the completion of their migration to the presumptive ganglion cell layer. These results suggest the following developmental sequence. (1) Ganglion cells of the posterior pole undergo their final mitosis near the ventricular margin between embryonic days 2 and 8. (2) They maintain contacts with both retinal surfaces and their nuclei move toward the ganglion cell layer. At this time they start to differentiate, expressing a form of neuron-specific tubulin and growing axons that can reach the optic chiasm. (3) Once migration is completed dendritic development commences.