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  • 1
    ISSN: 1432-1106
    Keywords: Acetylcholine ; Receptor antagonists ; Area 17 ; Mesencephalic reticular formation ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Stimulation of the mesencephalic reticular formation facilitates responses in the visual cortex elicited from the optic radiation. Using intraveneous administration of cholinergic antagonists we investigated in adult cats and two kittens whether this effect is mediated by cholinergic mechanisms. When administered alone the muscarinic antagonists atropine and scopolamine and the nicotinic antagonist mecamylamine failed to block reticular facilitation and sometimes even enhanced the effects of reticular stimulation. However, when administered in combination muscarinic and nicotinic antagonists eliminated or significantly reduced the facilitation. This was even true when the two antagonists were administered with a time lag of several hours. These results support the notion that reticular facilitation of cortical responses is mediated by cholinergic mechanisms and suggest that this effect is mediated either by a receptor with a mixed pharmacological property or by two independent pathways acting via nicotinic and muscarinic receptors. This hypothesis is discussed in the context of recent evidence on cholinergic transmission and earlier data on the pharmacology of reticular arousal.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1106
    Keywords: Excitotoxin lesion ; Basal forebrain ; Area 17 ; Mesencephalic reticular formation ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Cholinergic afferents to the neocortex controlled by the mesencephalic reticular formation (MRF) are known to transiently facilitate cortical excitability. In an attempt to identify the pathway mediating this effect in the cat visual cortex we combined retrograde tracing techniques with immunocytochemical methods to visualize the acetylcholine-synthesizing enzyme choline acetyltransferase (ChAT). In addition we examined, in acute electrophysiological experiments, whether local neurotoxin injections into nuclei of the basal forebrain interfered with the reticular facilitation of cortical evoked potentials. Cholinergic projections to area 17 originate from different centers in the homolateral substantia innominata/internal capsule, the septal nuclei, and the nuclei of the diagonal band of Broca. No direct cholinergic projection from the MRF to the visual cortex was observed. Retrogradely labelled cells intermingled with ChAT-positive neurons in the brainstem generally revealed immunopositivity for catecholaminergic markers. Local injections of neurotoxins in the substantia innominata blocked reticular facilitation, whereas local lesions of the septal nuclei and the nuclei of the diagonal band had no effect on MRF-induced facilitation. The blockage of the reticular facilitation of cortical evoked responses after unilateral lesions of the substantia innominata was bilateral, suggesting a cooperative interaction between basal forebrain structures of the two hemispheres. The anatomical and physiological data are discussed with respect to possible mechanisms of transient brainstem influences on cortical excitability.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 81 (1990), S. 257-266 
    ISSN: 1432-1106
    Keywords: Serotonin ; Area 17 ; Postnatal development ; Immunohistochemistry ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The laminar distribution and postnatal development of profiles immunoreactive to antibodies directed against serotonin (5-hydroxytryptamine, 5-HT) have been investigated in the primary visual cortex (striate cortex, area 17) of cats. In the adult cat, profiles with serotonin-like immunoreactivity consist exclusively of fibers which exhibit laminar differences in density and predominant orientation. Immunoreactive fibers are dense in layers I–III, less dense in layer V, and sparse in layers IV and VI. In layers I and VI the trajectories of these fibers are mainly tangential to the pial surface; in layers II–V they are predominantly radial and more irregular. The vast majority of immunoreactive fibers consists of fine axons with frequent small varicosities. In addition, there are a few thick axons. In 2-week-old cats, immunoreactive fibers are sparsely distributed through layers II–V. By 4 weeks, fiber density has decreased still further in layer IV and increased in layers I–III. By 6 weeks, the laminar pattern resembles that of adult cats except that fiber density is still lower than in adults. At three months of age, the mature pattern is established.
    Type of Medium: Electronic Resource
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