In order to determine what types of neurons in the striatum receive direct synaptic input from corticostriatal and thalamostriatal fibres and whether these afferents converge on individual striatal neurons, double anterograde labelling of axon terminals was combined with Golgi impregnation at both the light and electron microscopic levels. The area of the central neostriatum that receives input from both the parafascicular nucleus of the thalamus and the somatosensory cortex was identified by retrograde transport of a conjugate of horseradish peroxidase and wheat germ agglutinin (HRP-WGA). The same region of the neostriatum was studied in rats that had received multiple electrolytic lesions in the somatosensory cortex and also an injection of HRP-WGA in different parts of the parafascicular nucleus. Sections of this part of the neostriatum were impregnated by the single-section Golgi procedure after revealing anterogradely transported HRP-WGA. Twelve Golgi-impregnated spiny neurons were recovered and examined in the light and electron microscope after gold-toning. Ten of these neurons were typical very densely spiny medium-size neurons and they were all found to receive asymmetric synaptic input on dendritic spines from degenerating corticostriatal boutons. However, even though numerous boutons labelled anterogradely by HRP-WGA from the parafascicular nucleus were found within the dendritic fields of neurons that received cortical input, none of the terminals from the thalamus made synaptic contact with these neurons. Instead, all 96 thalamostriatal boutons studied were found in asymmetric synaptic contact with dendritic shafts of other neurons. Two such neurons that received input from the parafascicular nucleus were Golgi-impregnated and appeared to be medium-size spiny neurons, but they had a lower density of spines than the typical very densely spiny neurons. An independent confirmation that the targets of thalamostriatal neurons originating in the parafascicular nucleus are dendritic shafts was provided by studying the boutons labelled following electrolytic lesioning or injection of the lectin Phaseolus vulgaris-leucoagglutinin (PHA-L) into this nucleus: these boutons were also found to form asymmetric synaptic contacts with dendritic shafts within the neostriatum. It is concluded that although afferents from the somatosensory cortex and from the parafascicular nucleus converge upon the same part of the neostriatum, they probably do not converge upon the same spiny neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
The morphological organization of the monoamine-containing neurons in the brain of the sunfish (Lepomis gibbosus) was studied by means of the Falck-Hillarp histofluorescence method. No attempt was made to distinguish between norepinephrine and dopamine, both primary catecholamines (CA) yielding a similar yellow-green fluorescence after paraformaldehyde treatment. In the brain stem of this teleost fish, three groups of CA-containing neuronal somata have been found. First, there is a small collection of CA perikarya located just caudal to the obex of the fourth ventricle. The neurons of this medullo-spinal group give rise to numerous CA fibers many of which ascend within the central portion of the medulla. Intermingled with these CA fibers are some CA cells that constitute the cendral medullary group. The CA perikarya of this group are scattered between the levels of cranial nerves X and VIII. The tegmentum of the isthmus also contains a small group of very closely packed CA neurons. The large-sized CA cells of the isthmal group are located dorsolateral to the medial longitudinal fasciculus, partly within the periventricular gray. High densities of CA varicosities were also disclosed in various brain stem structures such as the optic tectum, the torus semicircularis and the cerebellar valvula. In addition, numerous serotonin (5-HTI-type neuronal somata were found in the raphe region of the brain stem, particularly a t caudal mesencephalic, isthmal and rostra1 medullary levels.A large number of CA cell bodies were visualized in the sunfish hypothalamus. Most of them form two populations of small, round cells that are located along and partly within the ependymal walls of the posterior and lateral recesses of the third ventricle. These bipolar cells possess one short club-like process protruding into the ventricle and their thin ependymofugal processes contribute to the CA innervation of numerous hypothalamic regions. Large CA neurons apparently without direct CSF contact also occur in the area of nucleus posterior tuberis, a t the level of the mesodiencephalic junction. Although the hypothalamic inferior lobes are devoid of CA cell bodies they are heavily innervated by CA axons.The sunfish telencephalon also receives a strikingly massive and complex monoaminergic innervation. Numerous CA fibers which are first observed a t the level of the preoptic area, ascend through the central zone of the telencephalon and arborize profusely particularly within the medial zone of area dorsalis telencephali. Other CA fibers, as well a s abundant fine 5-HT varicosities were found in the lateral zone of area dorsalis. Although the exact origin of the telencephalic CA afferents in Lepomis is not known, part of it may arise from the isthmal CA cell group which appears similar to the locus coeruleus of reptiles, birds and mammals. ' Reprint requests should be sent t o Dr. A, Parent,
The distribution of monoamine (MA)-containing nerve cell bodies in the brain stem of the chicken (Gallus domesticus) was studied by means of paraformaldehyde and glyoxylic acid fluorescent histochemical methods. The MA neurons were further characterized morphologically and histochemically in material prepared for the demonstration of acetylcholinesterase (AChE). In the rostral midbrain of the chicken, two large collections of catecholamine (CA)-containing cells are found: one located in the ventromedial and the other in the dorsolateral (pedunculopontine nucleus) portions of the tegmentum. On the basis of their topographic location, CA content, and fiber connections, these ventromedial and dorsolateral cell groups can be tentatively associated with the CA-containing neuronal populations of the mammalian ventral tegmental area and pars compacta of the substantia nigra, respectively. In the caudal midbrain of the chicken, numerous CA-containing cells are intermingled with serotonin (5HT)-containing perikarya beneath as well as within the decussation of the superior cerebellar peduncles. At isthmus levels, abundant, closely-packed CA-containing cells are encountered along the lateral border of the central gray. These neurons, which display a very high AChE activity, appear to be equivalent to those of the mammalian locus coeruleus. A multitude of medium-sized 5HT-containing neuronal somata occurs within the raphe region of the isthmus. Some of these somata closely surround the medial longitudinal fasciculus. This 5HT-containing cell group also massively invades the lateral tegmentum, where it becomes closely intermingled with the CA-containing neurons of the locus coeruleus and subcoeruleus. All of these 5 HT-containing neurons display a moderate to high AChE activity. In the medulla the number of MA-containing neurons is much smaller than in the upper brain stem. Nevertheless, 5HT-containing cells are present within the raphe region, particularly in the upper two-thirds of the medulla, and CA-containing perikarya can be found along the lateral border of the medulla and within the confines of the nucleus solitarius. The findings of the present study reveal that the MA-containing neuronal systems in the avian brain stem are organized according to a pattern that is much more complex than the one disclosed in reptiles or in other nonmammalian vertebrates. This complexity arises in large part from the fact that the 5HT-containing systems undergo a prominent lateralization in birds, which leads to a close intermingling of 5HT-containing and CA-containing neuronal elements at various levels of the neuraxis.
In order to investigate the neuronal populations projecting to the corpus striatum in the brain of a urodele, Triturus cristatus, horseradish peroxidase (HRP) retrograde labeling was used in parallel with anterograde degeneration, glyoxylic acid histofluorescence and behavioral testing. Striatal injections of HRP revealed that the main striatal afferent systems originate within the diencephalon, specifically in the dorsal thalamus and paraventricular organ of the hypothalamus. Several small groups of neurons in other diencephalic areas also participate in striatal innervation: proeminentia ventralis, amygdala, contralateral corpus striatum, preoptic area, posterior tuberal nucleus, locus coeruleus and raphe nuclei. Degeneration experiments after mechanical lesion of the paraventricular organ established the existence of a hypothalamostriatal projection. Degenerating axonal profiles were also found in many of the structures already identified as projecting to the striatum, suggesting that the paraventricular organ might influence the striatum not only directly but also indirectly through these other afferent systems. In the paraventricular organ, glyoxylic acid fluorescence histochemistry showed numerous monoamine neurons that corresponded in distribution and morphology to the retrogradely HRP-labeled neurons. Paraventricular-organ-lesioned males displayed a severe impairment of courtship behavior in the form of decreased tail beating and head stepping by the females. This suggests that the regulation of stereotyped hypermotricity might involve the monoamine component of the hypothalamostriatal projection.
The nature and function of the ionic channels at the apical membrane of primary cultured proximal tubule cells (PT) was investigated by use of the extracellular patch-clamp method. Several types of ionic channels were observed, including a calcium-dependent K+ channel of 206 pS in symmetrical 162 mM KCl activated at depolarizing potentials [maxi K+(Ca2+)]. Whole cell experiments were also carried out that clearly indicated that the PT cells respond to a hypotonic shock by activating electroconductive pathways. This response consisted of an initial hyperpolarization (from -47 to -58 mV, SD = 3, n = 4), followed by a strong depolarization (to -23 mV, SD = 4, n = 4). Furthermore, it was found in cell-attached experiments that the maxi K+(Ca2+) channel becomes activated during the hypotonic challenge. The activation process required external Ca2+, although some residual single-channel activity was measured in the absence of extracellular calcium (n = 3). On the basis of these results, it is concluded that the volume regulation process in PT cells in response to a hypotonic shock involves an influx of calcium from the external medium, which in turn triggers the opening of apical maxi K+(Ca2+) channels.
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