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

Abstract

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.

Water diffusion closely reveals neural activity status in rat brain loci affected by anesthesia

“…Although LFPs integrate “broad” electrophysiological changes, they are not strongly correlated with multi-unit activity (MUA) recordings, which directly reflect electric spiking of neurons. At this stage, one may only speculate that the ADC variations might reflect synaptic activity, originating from the integration at the MRI time scale (much longer than neuronal activity time scale) and spatial resolution of the dynamic swelling and shrinking of a very large number of dendritic spines continuously occurring upon their activation/deactivation status [28,60,65,66], as envisioned already by Ramon y Cajal more than a century ago (“The state of activity would correspond to the swelling and elongation of the [dendritic] spines, and the resting state (sleep or inactivity) to their retraction”) [67]. Dendritic spines are present in a very high density in mammal brain cortical tissue (approximately 1–2 × 10 9 /mm 3 in the human brain [68], 7 × 10 8 /mm 3 in the mouse cortex [69]) but not in organotypic slices, which are known to have a drastic reduction in the density of dendritic spines and functional synapses [70], perhaps explaining why neuronal activity did not correlate with any observable ADC change in such slices, although it was observed with cell swelling in extraphysiological conditions [14].…”

The ‘wet mind’: water and functional neuroimaging

“…In the small non-myelinated fibres of the garfish olfactory nerves (0.2-0.3 µm) swelling is in the order of 2 × 10 −2 µm 3 . Such a large excitation-induced swelling, which has been observed in various nerve tissues, including mammalian ganglion cells (Kusano and Tasaki 1990b), cannot easily be ascribed to a simple translocation of water from the extra-to the intracellular compartment, but can be better explained by an overall decrease in the density of the excited tissue (Tasaki and Byrne 1990).…”

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

“…ther low (3 mM) or high (10 mM) Ba2+ for a short period of time (not shown, but see Fig. 4B, top trace in the accompanying paper, Kusano and Tasaki, 1990). The heat generation in these preparations is very large, with the temperature of the preparation reaching about 1 O-' deg above the level before stimulation.…”