Shin-Ichi Terashima

Structure of warm fiber terminals in the pit membrane of vipers

The free nerve endings in the infrared receptor organ (the so-called “pit organ”) of an oriental pit viper, Trimeresurus f. flavoviridis, were studied with the electron microscope. The free nerve endings in this organ form a conglomeration of nonmyelinated nerve branchlets surrounding a few Schwann cells. We regard this conglomeration as a receptive unit, and have termed it the “terminal nerve mass”. Terminal nerve masses are about 40 μ in diameter and 10 μ thick; they are found in a single layer throughout the innervated membrane suspended in the pit cavity. The nerve branchlets comprising the masses contain a high concentration of mitochondria. Thin processes of the Schwann cells partially cover the surface of the branchlets, leaving certain areas completely bare. The structural relation between the Schwann cells and the branchlets seems functional, i.e., to provide the necessary nutrition for the cells without obstructing the reception of radiated energy over all the surface of the nerve mass. There are no synapses in the masses, indicating the absence of receptor interaction at this level of the receptor system.

Crotaline Pit Organs Analyzed as Warm Receptors

Afferent impulses from single-fiber preparations of the trigeminal nerve in Agkistrodon blomhoffi brevicauduswere recorded during steady and dynamic temperature stimulation of the sensory membrane in the facial pit. The thermoreceptors of the pit showed high sensitivity to the rate of change in receptor temperature. Changing the heat capacity of the pit membrane (a drop of water in the pit in the case of the laser and halogen lamp, and a drop of water covered by a plastic film in the case of flowing water) changed the pattern of response. When the heat capacity of the pit membrane is increased, responses approach those obtained in other warm receptors. The spatial gradient theory of Williams, whereby a reversal of heat energy flow is supposed to produce a reverse of response, was shown to be inapplicable to the pit receptors. Reversal of heat energy flow in the pits produced neither off-silence nor depression of response, and therefore direction of heat flow is not an important component of the stimulus for these receptors.

Infrared sensory neurons in the trigeminal ganglia of crotaline snakes: Transganglionic HRP transport

Trigeminal neurons were labeled by inserting HRP into holes cut in the pit receptor membranes of a crotaline snake, Agkistrodon blomhoffi brevicaudus. Neurons were labeled in the ophthalmic ganglion and the maxillary division of the maxillo-mandibular ganglion, and the HRP was further transported across the ganglia and through the lateral descending trigeminal tract (dlv) to label axon terminals exclusively in the dlv nucleus (DLV). In 6 successful preparations, 7.1-19.3% of totals of 5568-5986 cells in the maxillary division of the ganglion were labeled, but none at all were labeled in the mandibular division. Only a few or none at all were labeled in the ophthalmic ganglion. Cells in the two ganglia ranged in size from 10 to 55 micrometers, but large cells (greater than or equal to 40 micrometers) were scarce (4.9% of the total population). All HRP-labeled neurons fell in the median range of 20-39 micrometers. We concluded that these ganglion cells were infrared neurons, and were therefore the origin of the A delta fibers in the pit membrane. There were no HRP-labeled neurons above or below this range, in spite of the fact that smaller cells (less than or equal to 19 micrometers) made up 35.8% of the total population. In normal Nissl preparations we found both light- and dark-staining cells, but the size range of neither corresponded to the size range of infrared neurons.

Correlation between activity of the visual cortex and the somatovisual interaction in the lateral thalamus of cats

Summary In cats immobilized with Flaxedil, unitary responses to single radial nerve stimuli and to light flashes could be recorded in the contralateral thalamic reticular nucleus and the pulvinar region. From the same units, responses to single electric shock to the ipsilateral visual cortex were obtained. Cortically induced discharge patterns were mainly of two types: The first was a short latency train of repetitive bursts, the second was a long depression period followed by repetitive firing. Conditioning electrical stimuli of the visual cortex interacted in a complex fashion with the responses of thalamic units to visual, somatic and combined somatovisual stimulation; both facilitatory and inhibitory type interactions occurred. Strychnine application to the surface of the visual cortex elicited a remarkable increase of neuronal discharges at the thalamic level with respect to somatic, visual and the combined somatovisual stimuli. It is suggested from these results that the visual cortex and the thalamic reticular and pulvinar complex may work as a mechanism of perceptual integration involving the convergence of compound information from different sensory modalities.

Static response of infrared neurons of crotaline snakes—normal distribution of interspike intervals

Summary1.Background discharges (static responses) of warm fibers in the pit organs (infrared receptive organs) of two species of crotaline snakes were recorded at various temperatures (water, 18–33°C; air, 19–28°C). Mean interspike intervals

Central Response to Infra-Red Stimulation of the Pit Receptors in a Crotaline Snake, Trimeresurus Flavoviridis

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Generator potential of crotaline snake infrared receptor.

, standard deviations (SD), and coefficients of variation (CV) were calculated, and the goodness of fit of interspike interval histograms to a corresponding normal distribution (i.e., one having the same mean and SD) were tested.