Mammalian Superior Cervical Ganglion Research Articles

Chapter Two - Stereological and Allometric Studies on Neurons and Axo-Dendritic Synapses in Superior Cervical Ganglia

The superior cervical ganglion (SCG) plays an important role in neuropathies including Horner's syndrome, stroke, and epilepsy. While mammalian SCGs seem to share certain organizational features, they display natural differences related to the animal size and side and the complexity and synaptic coverage of their dendritic arborizations. However, apart from the rat SCG, there is little information concerning the number of SCG neurons and synapses, and the nature of relationships between body weight and the numbers and sizes of neurons and synapses remain uncertain. In the recognition of this gap in the literature, in this chapter, we reviewed the current knowledge on the SCG structure and its remodeling during postnatal development across a plethora of large mammalian species, focusing on exotic rodents and domestic animals. Instrumentally, we present stereology as a state-of-the-art 3D technology to assess the SCG 3D structure unbiasedly and suggest future research directions on this topic.

Rostro-caudal variations in neuronal size reflect the topography of cellular phenotypes in the rat superior cervical sympathetic ganglion

The mammalian superior cervical ganglion (SCG) contains a complex mixture of neuronal phenotypes that selectively innervate different peripheral targets. The present study examined the rostro-caudal topography of sympathetic phenotypes in the rat SCG by analyzing the relation between cell position, size, and the expression of immunoreactivity for neuropeptide Y (NPY), calretinin, and calcitonin gene-related peptide (CGRP). We observed that 64% of SCG neurons expressed NPY and had an average diameter of ∼24 μm throughout the ganglion. Previous studies indicate that most of these cells are vasoconstrictor in function. By contrast, the size of NPY-negative neurons varied from ∼25 μm in the rostral ganglion near the internal carotid nerve to ∼30 μm in the caudal ganglion between the external carotid nerve and cervical sympathetic trunk. Many of the large NPY-negative neurons in the caudal ganglion were surrounded by dense axonal baskets that were immunoreactive for calretinin and therefore are likely to be secretomotor neurons projecting to salivary glands. Consistent with earlier reports, the rostral ganglion contained low numbers of presumptive pupillomotor neurons, based on their expression of NPY and contact with fibers containing CGRP. The present results indicate that neuronal size may provide a useful aid to cellular identification, especially in the caudal ganglion, and they provide further evidence of a topographic organization within the mammalian SCG.

Mechanical changes associated with synaptic transmission in the mammalian superior cervical ganglion

Mechanical changes in the superior cervical ganglion (SCG) of the guinea pig, evoked by stimulating the pre- or postganglionic nerve, were determined by using a mechano-electric transducer. The mechanical change evoked by either one of these nerves was monophasic, an initial phase of rapid swelling (about 1 dyn/cm2) being followed by a slow relaxation. The mechanism of these mechanical changes was examined by treating the preparations with agents which are known to suppress or facilitate synaptic transmission in the SCG. Mechanical changes elicited by preganglionic nerve stimulation were suppressed by agents that reversibly block ganglionic transmission (Ca2(+)-free high Mg2+, d-tubocurarine, hexamethonium, TEA, TTX). On the other hand, agents which are known to facilitate synaptic transmission (high Ca2+) increased both the amplitude and the duration of swelling. In a Ba2(+)-containing medium, a large, long-lasting shrinkage of the ganglion was observed. It is suggested that the mechanical changes recorded in this study are associated with postsynaptic electro-genesis.

Heat generation associated with synaptic transmission in the mammalian superior cervical ganglion

By use of a thermal detector constructed with a thin polyvinylidene fluoride film (PVDF), heat production in the superior cervical ganglion (SCG) of the guinea pig was examined. A single electric shock applied to the preganglionic nerve evokes a temperature rise of approximately 1.5 x 10(-6) deg. The thermal responses summate when the preganglionic nerve is stimulated repetitively. The amplitude of the thermal response is increased when the preparation is treated with a high Ca2+ medium. Treatment with agents that block ganglionic transmission (high Mg2+, d-tubocurarine, hexamethonium, TTX) reversibly suppresses thermal response. It is thus concluded that the thermal responses described in this paper are generated by the physico-chemical events underlying postsynaptic electrogenesis in the SCG cells.

Pattern of presynaptic nerve activity can determine the type of neurotransmitter regulating a postsynaptic event.

The mammalian superior cervical ganglion has been the classical preparation for studying cholinergic transmission between neurones. Recently, however, evidence has been presented showing that, in addition to the postsynaptic changes mediated via nicotinic and muscarinic receptors, there is a non-cholinergic component to transmission in this ganglion, as in frog paravertebral ganglia. In the rabbit superior cervical ganglion, Ashe and Libet recorded a late, slow excitatory postsynaptic potential in response to preganglionic nerve stimulation in the presence of nicotinic and muscarinic antagonists. We have found, in the rat superior cervical ganglion, that a postsynaptic biochemical consequence of preganglionic nerve stimulation, namely the acute activation of tyrosine 3-monooxygenase (tyrosine hydroxylase, TH; EC 1.14.16.2), is mediated in part by acetylcholine and in part by a non-cholinergic neurotransmitter. The regulation of this enzyme activity is of particular interest because it catalyses the rate-limiting step in the biosynthesis of the postganglionic neurotransmitter, noradrenaline. In the present paper, we report that the relative importance of cholinergic and non-cholinergic transmission in the regulation of TH activity varies with the pattern of electrical stimulation of the preganglionic nerve trunk.

Catecholamines and cyclic nucleotides in the modulation of superior cervical ganglia

Four hypotheses have been advanced to explain the relationships between the cholinergic presynaptic afferents, principal ganglionic neurons, and small, intensely fluorescent (SIF) cells in synaptic transmission in the mammalian superior cervical ganglion (SCG). The first hypothesis involves the role of the dopaminergic SIF cell and cyclic AMP in the modulation of ganglionic transmission through the generation of a slow inhibitory postsynaptic potential (s-IPSP). The second concerns the generation of a slow excitatory postsynaptic potential (s-EPSP), and the role of dopamine and cyclic AMP in potentiating it. The third postulates that a presynaptic α-adrenergic receptor is responsible for inhibiting f-EPSP generation. A fourth hypothesis concerns the localization of the β-adrenergic receptor—adenylate cyclase complex in SCG. This paper discusses the evidence for each hypothesis, with special emphasis on species variations in the modulation of ganglionic transmission by catecholamines, adrenergic receptors, and cyclic AMP.

Embryologic development of a mouse sympathetic ganglion in vivo and in vitro.

The morphologic and biochemical development of the embryonic mouse superior cervical ganglion was characterized in vivo and in tissue culture. From 13 days of gestation, when the superior cervical ganglion was first visible, to birth at 19 days, tyrosine hydroxylase [tyrosine 3-monooxygenase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2] activity increased 100-fold in vivo. Explants of ganglia from 14-day embryos exhibited abundant neurite outgrowth in basal medium without added nerve growth factor (NGF), and increases in tyrosine hydroxylase activity paralleled that observed in vivo. Ganglia from 14-day embryos elaborated neurites and exhibited 3-fold increases in enzyme activity in vitro in the presence of antiserum to NGF (anti-NGF) or NGF + anti-NGF. In direct contrast, ganglia from 18-day fetuses failed to grow without added NGF or in medium containing anti-NGF or NGF + anti-NGF: virtually no axon outgrowth occurred and tyrosine hydroxylase activity decreased by half. These observations suggest that developmental regulatory mechanisms change radically during embryologic and fetal life of mammalian superior cervical ganglion.

Persistent innervation of mammalian sympathetic neurones by native and foreign fibres.

CONSIDERABLE evidence has been advanced to support the view that the reinnervation of adult mammalian autonomic neurones is specific1–4. Moreover, although foreign nerve fibres by themselves readily form synaptic connections with denervated ganglion cells5–11, when native fibres are also present their terminals are thought to be preferred to foreign axon terminals, which are eventually rejected4. I have re-examined the ability of neurones in the mammalian superior cervical ganglion (SCG) to select between native and foreign nerve fibres during reinnervation using the technique of intracellular recording. An unexpected result was that many neurones were initially reinnervated by both native and foreign nerves, and retained their dual innervation for at least 10 months.

Intracellular recording from mammalian superior cervical ganglion in situ.

1. Recordings have been obtained by intracellularly placed microelectrodes from cells of the superior cervical ganglion of the rabbit. The ganglion was left in situ.2. In response to stimulation of the external carotid nerve, some cells responded with a single spike of short latency followed by a long-lasting hyperpolarization. These cells, presumably, were activated antidromically. The majority of cells, however, responded with an early spike followed by a long-lasting depolarization; superimposed on this depolarization were one or two spikes with latencies from 35 to 70 msec. Anatomical pathways responsible for this activation have been suggested.3. A variety of responses were recorded from different neurones when the preganglionic sympathetic trunk was stimulated. Many of the cells responded to maximal stimulation of the nerve with repetitive spikes. Stimuli of constant strength could elicit variable responses from a single neurone. This variability and the multiple spike response may be due to multiple pathways leading to the same cell and the possibility of the presence of internuncial neurones in the ganglion is suggested.4. Strong stimulation of the preganglionic sympathetic nerve trunk caused inhibitory effects at the ganglion cells.5. Direct stimulation of the ganglion cells through the recording microelectrode elicited only one spike even at high intensity. Thus the multiple spike response to orthodromic stimulation must have been due to a temporally dispersed afferent input.6. It is concluded that the organization of the rabbit superior cervical ganglion is more complex than has been suspected previously, and that integration as well as transmission takes place at the level of these neurones.

On the Histology and Function of the Mammalian Superior Cervical Ganglion

On the Histology and Function of the Mammalian Superior Cervical Ganglion

On the Histology and Function of the Mammalian Superior Cervical Ganglion

On the Histology and Function of the Mammalian Superior Cervical Ganglion