Nerve processes and cell bodies containing leucine enkephalin were demonstrated in the sacral autonomic nucleus of the cat by immunocytochemical methods. Enkephalinergic preganglionic perikarya were seen only when axonal transport was blocked either by colchicine or by ventral root ligation. Ligation of the sacral ventral roots also produced damming of enkephalin immunoreactivity proximal to the S2 ligature. These data indicate that parasympathetic preganglionic neurons synthesize and transport enkephalin or enkephalin-like immunoreactive compounds to the periphery.

This study used antisera directed against glutamic acid decarboxylase (GAD), the biosynthetic enzyme for gamma-aminobutyric acid (GABA), to examine the light- and electron-microscopic distribution of presumed GABA-ergic synapses in the medullary homologue of the cat spinal dorsal horn, the trigeminal nucleus caudalis. At the light-microscopic level, immunoreactive terminals were concentrated in the superficial dorsal horn, laminae I and II. Colchicine was generally ineffective in revealing the distribution of cell bodies. However, in two successful cases, the majority of labeled cells were found in the magnocellular layer, ventral to the substantia gelatinosa, a region that had a lower density of immunoreactive terminals. Other labeled neurons were scattered in laminae I and II. A variety of synaptic arrangements were found at the electron-microscopic level. These derived from two types of labeled terminals. One contained both small round vesicles and large dense-cored vesicles. The second contained small round and pleomorphic vesicles. Some immunoreactive GAD terminals contained a few flat vesicles. Labeled terminals predominantly formed axodendritic synapses, via symmetrical contacts. Several axoaxonic arrangements were also observed. In most cases, the GAD terminal (which did not contain dense-cored vesicles) was presynaptic to another vesicle-containing profile, including the scalloped central terminal thought to derive from primary afferents. Another population of labeled GAD terminals was found postsynaptic to unlabeled vesicle-containing profiles, including central terminals. These data indicate that inhibitory GABA-ergic controls in the trigeminal nucleus caudalis involve both presynaptic and postsynaptic mechanisms and are probably mediated via direct contacts onto ascending projection neurons, as well as via synaptic contacts onto nociceptive primary afferent fibers. The transmission of nociceptive messages by neurons of the spinal cord dorsal horn and trigeminal nucleus caudalis is subject to a variety of segmental and supraspinal controls. Pharmacological and electrophysiological studies have implicated the biogenic amines serotonin and norepinephrine, and the endogenous opioid peptides enkephalin and dynorphin, in those controls (Basbaum and Fields, 1978, 1984; Basbaum et al., 1983; Basbaum, 1985).(ABSTRACT TRUNCATED AT 400 WORDS)

This study examined the spinal cord distribution of the endogenous opioid peptide leucine-enkephalin in the cat using immunohistochemical techniques. The distribution of nerve processes was studied in untreated cats; colchicine was administered to study the distribution and morphology of spinal enkephalin-containing perikarya. Enkephalin immunoreactive processes were greatest in laminae I and II (marginal layer and substantia gelatinosa) of the superficial dorsal horn. In many sections, the outer substantia gelatinosa (SG), lamina IIa, was discernibly less immunoreactive than I or IIb. Laminae III and IV were relatively devoid of staining. Laminae V and VII had moderate enkephalin-immunoreactivity, lamina VI somewhat less. Enkephalin immunoreactivity in lamina X, around the central canal, was very dense. Enkephalin-containing beaded varicosities coursed throughout the ventral horn. Although previous studies in the rat emphasized the enkephalin-somata of the SG, we found that in the cat the majority of superficial dorsal horn enkephalin-somata are in the marginal layer. These enkephalin-containing marginal cells were morphologically similar to a population of marginal neurons which project to the brainstem and/or the thalamus. Some light staining small SG neurons were also identified; many were located at the lamina I-II border. Considerably more cells were found ventral to the SG, in lamina III, and at the IV-V border. These latter cells had dendrites coursing dorsally, toward the SG. Numerous immunoreactive cells were found in lamina VIII, in a band across the intermediate gray. These cells fused medially with cells of lamina X. Enkephalin cells were also found in the sacral autonomic nucleus and encircling the central cervical nucleus, Clarke's column, and stilling's nucleus. Although surrounded by labeled cells, the latter regions were devoid of enkephalin-immunoreactive processes. Many of these spinal enkephalin neurons are morphologically similar to and distributed in regions known to contain projection neurons. Thus it is suggested that many spinal enkephalin neurons, generally thought to be local circuit neurons, project rostrally, to other spinal levels and perhaps to brainstem and/or thalamus.

1 The contribution of vasomotor tone to the increased stiffness of carotid arteries in living spontaneously hypertensive rats (SHR) is largely unknown. Whether a reduced vascular tone is associated with an increase or a decrease in arterial stiffness in vivo remains to be determined. The goal of the present investigation was to show that a decrease in vascular tone is associated with a decrease in arterial stiffness, independent of the structural composition of the arterial wall. 2 New high resolution echo-tracking techniques were used to evaluate pulsatile changes of carotid blood pressure and diameter following transient and graded changes of vasomotor tone produced by the dihydropyridine derivative, isradipine. Treatment for 8 weeks was given to groups of SHR rats either with a low (0.6 kg day-') or a high (2.6 mg kg-l day-') dose. Another SHR group received an acute dose of 2.6 mg kg-' day-'. Results were compared to those of placebo-treated Wystar-Kyoto (WKY) and SHR rats. Whatever the dosage, acute or chronic calcium blockade caused a decrease in blood pressure which was maximal 1 h after administration and disappeared after the 16th h. Carotid arterial thickness and the composition of the arterial wall was determined from histomorphometry. 3 In placebo-treated SHR, the inverse relationship relating blood pressure to carotid arterial distensibility was significantly shifted toward higher values of blood pressure compared to the curve of normotensive placebo-treated WKY rats. The curve of SHR receiving chronically a non antihypertensive (0.6 mg kg`' day-') isradipine dose prolonged that of placebo-treated SHR toward lower values of blood pressure, so that carotid distensibility was significantly higher than in WKY for the same diameter and blood pressure level (145 mmHg). With administration of a chronic antihypertensive dose (2.6 mg kg-' day-') causing a significant decrease in arterial thickness, the curve of SHR was transiently shifted towards the WKY curve, resulting in a normal arterial function. Acute antihypertensive calcium blockade with a single isradipine dose (2.6 mg kg-' day-') caused a similar shift in the pressure-distensibility curve toward the WKY curve although the histomorphometric composition of the arterial wall differed significantly from that of chronically treated animals. 4 The study provides evidence that, in living SHR submitted to calcium blockade, (i) a low dose of isradipine causing no substantial antihypertensive effect is associated with a significant elevation of carotid arterial distensibility for the same pressure and diameter as normotensive controls, and (ii) an acute or chronic dose causing a substantial antihypertensive effect is associated with a transient shift of the SHR distensibility-pressure curve toward a physiological arterial function, increasing carotid distensibility for the same pressure and diameter as WKY controls. Since such findings were observed independently of the histomorphometric composition of the arterial wall, they imply that the transient decre...

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