Macrophages in Pacinian corpuscles

The presence of macrophages in the outer bulb region of mouse, monkey and human Pacinian corpuscles was demonstrated by light and electron microscopy. In the normal, nontreated, Pacinian corpuscles, a few particular cells were located in the spaces between lamellae of the outer bulb. These cells contained numerous vesicles and vacuoles, and various cytoplasmic processes. When horseradish peroxidase (HRP) was injected locally or systemically, many HRP-positive cells, which were considered to be similar to the particular cells described above, were found in the outer bulb region of the corpuscles. Electron microscopy revealed that these cells contained HRP in vesicles and vacuoles, suggesting that they were macrophages vigorously taking up exogenous HRP. Macrophages in the Pacinian corpuscles are considered to work as scavengers to keep the inner environment of the corpuscles clear and constant with regard to its macromolecular content.     

Mg, Ca-activated ATP-ase of Pacinian corpuscles]

Adenosine triphosphatase (ATPase) activated by Mg2+ or Ca2+ ions was detected in single mechanoreceptors (Pacini's corpuscles) of cat; addition of Ca2+ (10(-5)M) to Mg-ATP-ase increased the activity by the factor of 1.6. The activity optimum of Mg- or Co-ATPase was in the alkaline pH zone. A high substrate specificity of Mg, Ca-ATPase was shown. Parachlorinemercury-benzoate (5muM) considerably reduced the activity of Mg, Ca-ATPase, whereas oubain (10(-5)M) failed to affect it significantly. It is supposed that Mg, Ca-ATPase of Pacini's corpuscles was close to actomyosine -like proteins.     

A re-evaluation of the cytology of cat Pacinian corpuscles

Summary The aesthetascs of the spiny lobster, Panulirus argus, are hair sensilla located on the lateral filaments of the antennules. Each hair is about 0.8 mm long and innervated by about 320 bipolar sensory neurons, the dendrites of which project as a bundle into the hair shaft. Each of the dendrites develops two cilia. Within a very short distance each of these cilia branches repetitively and dichotomously resulting in 8000 to 10000 outer dendritic segments per hair, or about 20 to 30 branches per neuron. The branches intertwine frequently before running to the tip of the hair. Each hair also possesses inner and outer auxiliary cells. The inner auxiliary cells surround the bundle of dendrites, extending distally to the origin of the ciliary segments. Extensions of these cells project into the bundle of dendrites, separating groups of dendrites into discrete clusters. Outer auxiliary cells wrap the inner ones, but do not extend beyond the base of the hair.     

A re-evaluation of the cytology of cat Pacinian corpuscles

Summary The ultrastructure of cat mesenteric Pacinian corpuscles in cross and longitudinal sections has been examined. The terminal ends of lamellar cells of the inner core have been identified in longitudinal sections through the proximal portion of the inner core. These terminal bulbous expansions contain characteristic concentric membranes of rough endoplasmic reticulum and in some cases masses of oval membranous inclusions. The central axon as seen in cross section is oval in profile, having X-(short) and Y-(long) axes, and each axonal face is characterized by specializations of the axolemma. At the X-axis, the inner lamellae of the inner core tightly abut a smooth axolemma, with no intervening connective tissue matrix, in a manner reminiscent of a neuroepithelium. The axolemma of the Y-axis has numerous axonal spines (microspikes) that project into the cleft in the inner core. The extent of the axolemma having axonal spines can only be appreciated in longitudinal sections. The clefts contain a specialized connective tissue with elastic and collagen fibrils. The connective tissue compartment of fibers and matrix separating individual inner core lamellae is unique, in that it contains extremely thin collagen fibrils measuring approximately 15 nm in diameter. The diameter of collagen fibrils increases as the cleft is approached. Here the fibrils resemble typical endoneural collagen.     

Survival of Pacinian corpuscles after denervation in adult rats

Summary The ultrastructure of Pacinian corpuscles located on the crural interosseous membrane was studied in adult rats 6 h to 10 months after transection of the right sciatic nerve. Axon terminals degenerated one day after transection and were engulfed and resorbed by cells of the inner core within one week. The axial space left after removal of the axonal debris was closed by the lamellae of the inner core. The main structural features of the inner core and capsule remained preserved after denervation throughout the period of study. The denervated inner cores, however, became atrophic 10 months after neurotomy, their mean diameter being reduced by 17.5% compared with that of contralateral control corpuscles. The number of capsular lamellae was unaltered, and perineurial pathways of the peripheral nerve stump remained preserved. Schwann cells proliferated and formed Büngner bands during the first month after denervation, but retracted their processes and became atrophic at later stages after neurotomy.Survival of Pacinian corpuscles after long-term denervation in adult rats is in contrast to their rapid degeneration within several days after nerve section in neonates.     

Mesenteric and tactile Pacinian corpuscles are anatomically and physiologically comparable

Pacinian corpuscles (PCs) in cat mesentery have been studied extensively to help determine the structural and functional bases of tactile mechanotransduction. Although we, like many other investigators, have found that the mesenteric receptors are anatomically very similar to those found in mammalian skin, few physiological characteristics of the mesenteric PCs and those of the skin have been compared. Action-potential rate-amplitude and frequency characteristics (10 Hz–1 KHz), as well as interval (IH) and peri-stimulus-time (PSTH) histograms in response to sinusoidal displacements were obtained from nerve fibers innervating mesenteric PCs and from PC fibers innervating cat glabrous skin. The intensity characteristics obtained on both preparations showed similar response profiles, including equal slopes for low stimulus intensities (approximately 10, with impulse ratios/20 dB displacement) and one and two impulse/cycle entrainment. The frequency characteristics of both groups were U-shaped with similar low-frequency slopes (?12.5 dB/octave) and bandwidths (Q_3dB = 1.4). The best frequency for both the tactile PCs' and mesenteric PCs was 250 Hz, which is in the expected range. The IHs showed entrainment and the PSTHs showed neither transient responses nor adaptation to steady-state sinusoidal stimuli. The functional similarity between mesenteric PCs' nerve responses and those of tactile PC afferents, as well as the receptors’ anatomical similarity, lead us to suggest that the mesenteric PC can act as a model for those in the skin. Furthermore, since the frequency characteristics of the two PC types are similar, it is concluded that the skin, while attenuating stimulus intensity, does not impart temporal filtering of vibratory stimuli.     

Mesenteric and tactile Pacinian corpuscles are anatomically and physiologically comparable

Pacinian corpuscles (PCs) in cat mesentery have been studied extensively to help determine the structural and functional bases of tactile mechanotransduction. Although we, like many other investigators, have found that the mesenteric receptors are anatomically very similar to those found in mammalian skin, few physiological characteristics of the mesenteric PCs and those of the skin have been compared. Action-potential rate-amplitude and frequency characteristics (10 Hz-1 KHz), as well as interval (IH) and peri-stimulus-time (PSTH) histograms in response to sinusoidal displacements were obtained from nerve fibers innervating mesenteric PCs and from PC fibers innervating cat glabrous skin. The intensity characteristics obtained on both preparations showed similar response profiles, including equal slopes for low stimulus intensities (approximately 10, with impulse ratios/20 dB displacement) and one and two impulse/cycle entrainment. The frequency characteristics of both groups were U-shaped with similar low-frequency slopes (-12.5 dB/octave) and bandwidths (Q(3dB) = 1.4). The best frequency for both the tactile PCs' and mesenteric PCs was 250 Hz, which is in the expected range. The IHs showed entrainment and the PSTHs showed neither transient responses nor adaptation to steady-state sinusoidal stimuli. The functional similarity between mesenteric PCs' nerve responses and those of tactile PC afferents, as well as the receptors' anatomical similarity, lead us to suggest that the mesenteric PC can act as a model for those in the skin. Furthermore, since the frequency characteristics of the two PC types are similar, it is concluded that the skin, while attenuating stimulus intensity, does not impart temporal filtering of vibratory stimuli.     

Effect of catecholamines on excitability of single mechanoreceptors of Pacinian corpuscles

A method of continuous external perfusion was used to study the effect of adrenalin and noradrenalin on the excitability of single isolated mechanoreceptors of Pacinian corpuscles. On the addition of adrenalin and noradrenalin in concentrations of 1·10^–5–1·10^–7 g/ml to the solution the excitability of the receptors was increased by 10–15% and the amplitude of the receptor potential rose on the average by 10–20%. It is postulated that the change in excitability is due to an increase in the receptor membrane potential. The results are discussed in connection with the possible adrenergic innervation of the Pacinian corpuscles.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 6, No. 3, pp. 312–317, May–June, 1974.     

Possible glutaminergic interaction between the capsule and neurite of Pacinian corpuscles

The role of the capsule encasing the Pacinian corpuscle's (PC's) neurite, where mechanotransduction occurs, may be more than mechanical. The inner core of the PC's capsule consists of lamellar cells that are of Schwann-cell origin. Previously, we found both voltage-gated Na+ and K+ channels in these inner-core lamellae. Research on astrocytes and Schwann cells shows bidirectional signaling between glia and neurons, a major component of which is glutamate. Furthermore, Merkel cells show positive immunoreactivity for glutamate receptor mGluR5, and the glutamate-receptor antagonist kynurenate greatly decreases the static activity of the slowly adapting neurons of Merkel cell-neurite complexes. To investigate the possibility of glutaminergic interaction in PCs, we applied antibodies to glutamate, glutamate receptors, glutamate transporters, and SNARE proteins to cat mesenteric PC sections. Positive labeling was seen in the inner-core lamellae, at inter-lamellar connections, where the lamellae contact the membrane of the neurite and at the lamellar tips. The presence of these proteins on the lamellae and neurite membranes, demonstrated both with immunofluorescent light microscopy as well as immunogold electron microscopy, suggests a chemical, possibly bidirectional, interaction between the lamellar cells and the neurite. Thus, the capsule of the PC, apart from having a mechanical filtering function, may also provide an environment for lamellar-neurite interaction, perhaps acting as a neuro-modulator of the initiation, and/or continuation, of the mechanical-electrical transduction process. At the very least, the presence of the aforementioned proteins suggest some sort of "synaptic-like" activity in these mechanoreceptors, which up until now has not been considered possible.