Distribution of neuropeptide Y-like immunoreactive perikarya and processes in the medulla of the cat

Central control of atrio-ventricular conduction and left ventricular contractility in the cat heart: Synaptic interactions of vagal preganglionic neurons in the nucleus ambiguus with neuropeptide Y-immunoreactive nerve terminals

In the cat, vagal postganglionic controls of heart rate, atrio-ventricular (AV) conduction and left ventricular contractility are mediated by three separate intrinsic cardiac ganglia, the sinoatrial (SA), AV and cranioventricular (CV) ganglia, respectively. The vagal preganglionic neurons (VPNs) that project to these ganglia are located in the ventrolateral nucleus ambiguus (NA-VL). We have previously shown that the VPNs projecting to the SA, AV and CV ganglia are distinct from one another. We have also demonstrated that neuropeptide Y-immunoreactive (NPY-IR) axon terminals synapse upon VPNs projecting to the SA ganglion. In the present study, we test the hypothesis that those VPNs projecting to the AV ganglion (negative dromotropic VPNs) and those projecting to the CV ganglion (negative inotropic VPNs) are innervated by NPY-IR terminals in NA-VL. A retrograde tracer was injected into the AV or CV ganglion of the cat, and the brains subsequently processed for visualization of tracer and the immunocytochemical visualization of NPY by dual labeling electron-microscopic methods. We observed that 11+/-5% of all axodendritic synapses and 8+/-6% of all axosomatic synapses upon negative inotropic VPNs were NPY-IR. Furthermore, 19+/-14% of all axodendritic synapses upon negative dromotropic VPNs were NPY-IR. A few NPY-IR axosomatic synapses upon negative dromotropic neurons were also observed. NPY-IR terminals in NA-VL occasionally formed axosomatic synapses with NPY-IR neurons and axoaxonic synapses with unlabeled terminals. These results suggest that central NPY afferents to the NA-VL modulate the vagal preganglionic control of AV conduction and left ventricular contractility.

Enkephalins and functionally specific vagal preganglionic neurons to the heart: Ultrastructural studies in the cat

In cat, distinct populations of vagal preganglionic and postganglionic neurons selectively modulate heart rate, atrioventricular conduction and left ventricular contractility, respectively. Vagal preganglionic neurons to the heart originate in the ventrolateral part of nucleus ambiguus and project to postganglionic neurons in intracardiac ganglia, including the sinoatrial (SA), atrioventricular (AV) and cranioventricular (CV) ganglia, which selectively modulate heart rate, AV conduction and left ventricular contractility, respectively. These ganglia receive projections from separate populations of vagal preganglionic neurons. The neurochemical anatomy and synaptic interactions of afferent neurons which mediate central control of these preganglionic neurons is incompletely understood. Enkephalins cause bradycardia when microinjected into nucleus ambiguus. It is not known if this effect is mediated by direct synapses of enkephalinergic terminals upon vagal preganglionic neurons to the heart. The effects of opioids in nucleus ambiguus upon AV conduction and cardiac contractility have also not been studied. We have tested the hypothesis that enkephalinergic nerve terminals synapse upon vagal preganglionic neurons projecting to the SA, AV and CV ganglia. Electron microscopy was used combining retrograde labeling from the SA, AV or CV ganglion with immunocytochemistry for enkephalins in ventrolateral nucleus ambiguus. Eight percent of axodendritic synapses upon negative chronotropic, and 12% of axodendritic synapses upon negative dromotropic vagal preganglionic neurons were enkephalinergic. Enkephalinergic axodendritic synapses were also present upon negative inotropic vagal preganglionic neurons. Thus enkephalinergic terminals in ventrolateral nucleus ambiguus can modulate not only heart rate but also atrioventricular conduction and left ventricular contractility by directly synapsing upon cardioinhibitory vagal preganglionic neurons.

Distribution of neuropeptide Y-immunoreactive neurons in the human brainstem, cerebellum, and cortex during development

1. Neuropeptide Y is found throughout the central nervous system where it appears to play a wide range of often poorly understood functions. In this study, the distribution of neuropeptide Y immunoreactive (NPY-ir) neurons in the brainstem, cerebellum, and cerebral cortex of human fetuses ranging in age from 11 gestational weeks to term was investigated by immunohistochemistry. 2. The NPY-ir cells were detected in the dorsal and ventral rostral midbrain and the interpeduncular nucleus by 21 weeks and 32 weeks of gestation, respectively. Although no positive cells were found in the pons, the NPY-ir fibers were detected there at 32 gestational weeks. 3. The vagal, hypoglossal, and olivary nuclei of the medulla oblongata contained immunoreactive cells by week 21 and the medullary reticular formation by week 25 of gestation. In most of these locations, both the number and size of neuropeptide Y positive cells were greater at birth and reached maximal values of 100-400 cells per 1 mm2 and 2-5 microm in diameter, respectively. 4. In the cerebellum, numerous NPY-ir horizontal and granule cells, as well as the cells within the dentate nucleus were observed as early as 21 weeks of gestation. 5. The NPY-ir cells were also detected in the developing cerebral cortex, with the earliest activity observed within the temporal cortex at 14 weeks of gestation. By week 21, positive cells appeared in the visual, frontal, sensory, and motor cortices. Most of these cells were bipolar or multipolar in morphology but their numbers at birth were relatively low. 6. Our results show a wide distribution of the NPY-ir cells in the developing human brain and offer supporting evidence for the important modulatory role of NPY in both the fetus and adult.

Parasympathetic control of the heart. III. Neuropeptide Y-immunoreactive nerve terminals synapse on three populations of negative chronotropic vagal preganglionic neurons

The vagal postganglionic control of cardiac rate is mediated by two intracardiac ganglia, i.e., the sinoatrial (SA) and posterior atrial (PA) ganglia. Nothing is known about the vagal preganglionic neurons (VPNs) that innervate the PA ganglion or about the neurochemical anatomy of central afferents that innervate these VPNs. These issues were examined using light microscopic retrograde labeling methods and dual-labeling electron microscopic histochemical and immunocytochemical methods. VPNs projecting to the PA ganglion are found in a narrow column exclusively in the ventrolateral nucleus ambiguus (NA-VL). These neurons are relatively large (37.6 +/- 2.7 microm by 21.3 +/- 3.4 microm) with abundant cytoplasm and intracellular organelles, rare somatic and dendritic spines, round uninvaginated nuclei, and myelinated axons. Previous physiological data indicated that microinjections of neuropeptide Y (NPY) into the NA-VL cause negative chronotropic effects. The present morphological data demonstrate that NPY-immunoreactive nerve terminals formed 18 +/- 4% of the axodendritic or axosomatic synapses and close appositions on VPNs projecting to the PA ganglion. Three approximately equal populations of VPNs in the NA-VL were retrogradely labeled from the SA and PA ganglia. One population each projects to the SA ganglion, the PA ganglion, or to both the SA and PA ganglia. Therefore, there are both shared and independent pathways involved in the vagal preganglionic controls of cardiac rate. These data are consistent with the hypothesis that the central and peripheral parasympathetic controls of cardiac rate are coordinated by multiple potentially redundant and/or interacting pathways and mechanisms.

Ultrastructural study of NADPH-d positive neurons in laminae I and II of the rat caudal spinal trigeminal nucleus

The present study investigated the ultrastructure of neurons in the caudal spinal trigeminal nucleus. These neurons which are believed to function as interneurons in the transmission of orofacial nonreflexive nociceptive information, measured 20 microns x 11 microns, and were nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) positive. The reaction product, formazan, was localized in the nuclear envelope, mitochondria, rough endoplasmic reticulum, and multivesicular bodies of these neurons. It was also localized in the membrane of the smooth endoplasmic reticulum at the axon terminal. The neurons were contacted by both axosomatic and axodendritic synapses formed by both NADPH-d positive and NADPH-d negative axon terminals. Two types of NADPH-d positive axon terminals could be recognized. The first was a large terminal containing many stained mitochondria and unstained small round agranular vesicles mixed with some slightly flattened ones. It formed asymmetrical axodendritic synapse. The second type of axon terminals contained pleomorphic synaptic vesicles and formed asymmetrical synapses upon both dendrites and soma. The sources of NADPH-d positive axon terminals were discussed. Most of the unstained axon terminals forming axosomatic and axodendritic synapses with stained cell bodies and dendrites contained flattened vesicles. In addition to the above, complicated synaptic configurations showing NADPH-d positive axoaxonic synapses in relation to NADPH-d negative dendritic spines were also seen in which a NADPH-d negative dendritic spine was completely contacted by a NADPH-d positive bouton which was in turn contacted by another NADPH-d positive bouton.

Immunohistochemical study of catecholamine enzymes and neuropeptide Y (NPY) in the rostral ventrolateral medulla and bulbospinal projection

The purpose of this study was to determine whether neuropeptide Y (NPY) terminals in the intermediolateral spinal cord originate from the rostral ventrolateral medulla (RVLM). Immunohistochemical staining of tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), phenylethanolamine-N-methyltransferase (PNMT), and NPY in the rat brainstem and spinal cord were performed in this study in order to examine consequences of lesions of the RVLM and of intracisternal injections of 6-hydroxydopamine (6-OHDA) on catecholamine and NPY immunoreactivity in the intermediolateral column (IML) of rats. In addition, ricin, a retrograde neurotoxin, was applied in the superior cervical ganglion (SCG) to determine its effect on catecholamine and NPY immunoreactivity in the IML. Computer-aided image analysis was used to quantify the immunohistochemical changes in the RVLM and spinal cord. The results demonstrated that many catecholamine- and NPY-containing neurons and/or fibers existed in the RVLM and their terminals were found in the IML. After administration of 6-OHDA intracisternally, the catecholamine and NPY immunoreactivities were decreased both in the brainstem and IML of the spinal cord. Following unilateral microinjection of 6-OHDA into the RVLM, the number of NPY- and catecholamine-containing neurons decreased and there was a reduction in neuron terminals on the ipsilateral side. After injection of ricin into the SCG, the catecholamine and NPY neurons of the medulla were not affected, whereas their terminals in the IML decreased ipsilaterally. These results indicate that most of the catecholamine- and NPY-immunoreactive terminals found in the IML originated in the RVLM. These terminals appear to project towards the superior cervical ganglia.

Rostrocaudal differences in morphology and neurotransmitter content of cells in the subretrofacial vasomotor nucleus

The rostral ventrolateral medulla (RVLM) contains sympathoexcitatory neurons that exert a powerful control over the sympathetic outflow to the cardiovascular system. In the cat there is a concentration of such neurons (but not neurons subserving other functions) within a narrow longitudinal column in the RVLM termed the subretrofacial (SRF) nucleus. Furthermore, it has been suggested that there are subgroups of cells, located at different rostrocaudal levels of the SRF nucleus, that preferentially or exclusively control different vascular beds (e.g. in the kidney and hindlimb). The aim of this study was to map quantitatively the rostrocaudal distribution within the nucleus of different cell types, defined according to morphological and/or chemical criteria, and to correlate this with the regional vasomotor effects (in hindlimb and kidney) evoked by stimulation of SRF cells at the corresponding rostrocaudal levels. SRF cells were highly heterogeneous with respect to both their morphology and chemical properties. They varied greatly in size (equivalent diameter ranging from 10-40 microns) as well as in shape and orientation. An immunohistochemical examination using the avidin-biotin procedure revealed that many SRF cells (estimated 57% of all SRF cells) were immunoreactive for tyrosine hydroxylase (TH, a marker of catecholamine cells). In addition, there were SRF cells immunoreactive for neuropeptide Y (NPY, 11% of total), enkephalin (ENK, 16% of total), and serotonin (5HT, 10% of total), but not for substance P, galanin or somatostatin. Different cell types, defined according to their morphology and/or chemical properties, were unevenly distributed throughout the nucleus. In the most caudal part of the SRF nucleus, virtually all cells were TH-positive, and the large majority (estimated 80%) were NPY-positive, suggesting that many cells at this level contained both TH and NPY. In contrast, in the most rostral part of the SRF nucleus, only 30% of cells were TH-positive, and no NPY-positive cells were observed. Both 5HT- and ENK-positive cells were found throughout the rostrocaudal extent of the nucleus, but predominantly within its rostral part. Furthermore, TH-positive cells in the rostral SRF nucleus were on average significantly larger (mean equivalent diameter 18-43% greater) than TH/NPY-positive cells in the caudal part of the nucleus, but smaller than 5HT- or ENK-positive cells at the same level. Overall, rostral cells (regardless of their chemical type) were larger than caudal cells within the SRF nucleus (mean equivalent diameter 13-28% greater).(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural localization of neuropeptide Y-like immunoreactivity in the rat hippocampal formation

Neuropeptide Y (NPY) has been implicated in the modulation of hippocampal neuronal activity and in the pathophysiology of several neurological disorders involving the hippocampal formation. Thus, this study examines the light and electron microscopic immunoperoxidase labeling of a rabbit polyclonal antibody against porcine NPY in single sections through each lamina of the CA1 and CA3 regions of the hippocampus and the dentate gyrus (DG) of normal adult rats. By light microscopy, the majority of perikarya with intense NPY-like immunoreactivity (NPY-LI) were located in stratum oriens of CA1 and CA3 of the hippocampus and in the hilus of the DG. Fine varicose processes with NPY-LI were found in all layers of the hippocampal formation, but were densest in the outer third of the molecular layer of the DG. The density of NPY-labeling was greater in the ventral portion of the hippocampal formation. By electron microscopy, most NPY-containing perikarya in all three hippocampal regions were: small (8-12 microns) or medium-sized (12-18 microns) and elongated; or medium-sized and round. A dense accumulation of NPY-LI was commonly observed within the individual saccules of Golgi complexes and some rough endoplasmic reticulum in the cytoplasm. Perikarya and dendrites with NPY-LI usually were directly apposed to other neuronal processes (mostly terminals) and lacked astrocytic appositions. The majority of terminals in contact with NPY immunoreactive neurons were unlabeled and synapsed with the shafts of large and small dendrites. In CA1 and CA3 of the hippocampus, the types of synapses formed by the unlabeled terminals were not significantly different; however, more asymmetric synapses than symmetric synapses were formed by the unlabeled terminals on the shafts of small NPY-labeled dendrites in the DG. The terminals with NPY-LI (0.25-1.2 microns) contained many small, clear vesicles and 0-2 large, dense-core vesicles. The types of synapses (i.e., asymmetric and symmetric) and distribution of NPY-labeled terminals on the targets were remarkably similar in each lamina of the hippocampal subregions. The NPY-labeled terminals usually synapsed with one unlabeled perikaryon or dendrite. However, others synapsed either (1) with two unlabeled perikarya or dendrites simultaneously or (2) with one NPY-containing perikaryon or dendrite. Most of the terminals with NPY-LI formed symmetric junctions with the shafts of small (distal) dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)

Estrogen and the etiology of anorexia nervosa

Most patients suffering from anorexia nervosa are women, but the types and relative contributions of social, psychological, or organic characteristics of women that make women more likely to develop this feeding disorder are uncertain. In this theoretical review, evidence that the female sex hormone, estrogen, contributes to the symptoms seen in anorexia and underlies the sex difference in incidence is discussed. Current data on the anorexic potency of estrogen in experimental animals, humans, and in anorexic patients is presented, along with a suggestion that treatment of anorexics with progesterone, a hormone that blocks these effects of estrogen, might have a beneficial influence upon the outcome of anorexia nervosa.