Cholinergic tracing of a central neural circuit underlying the thirst drive

Cholinergic stimulation of any of a number of interrelated limbic and diencephalic structures in the rat elicits a rapid and marked increase in water intake. We postulate that a generalized Papez circuit mediates the thirst drive, that the circuit is specifically and functionally sensitive to cholinergic action, and that other primary drives depend on closely parallel neural circuits partitioned both structurally and biochemically.

CENTRIFUGAL FIBRES IN THE AVIAN VISUAL SYSTEM

A study has been made of the origin and course of the centrifugal fibres in the visual pathway of the pigeon using the Nauta method. Lesions in the mid-brain involving the isthmo-optic nucleus result in fibre degeneration which can be traced through the isthmo-optic tract to the chiasma and thence into the contralateral optic nerve and retina. In the retin a severe degeneration is found throughout the optic nerve layer, and occasional degenerating fibres can be traced through the ganglion cell layer to the inner aspect of the bipolar cell layer. Here they terminate in endings similar to those described by Cajal (1889) and Dogiel (1895) in relation to amacrine cells. The projection to the retina is completely crossed. Counts of the number of cells in the isthmo-optic nucleus indicate that the number of centrifugal fibres is approximately 10000; they form 1 % of the total number of fibres in the optic nerve. The isthmo-optic nucleus receives afferents from the tectum, and in this projection there would appear to be a well-defined organization.

RESPIRATORY PERIODICITY IN THE PARALYZED, VAGOTOMIZED CAT: HYPOCAPNIC POLYPNEA

The phrenic nerve discharge was recorded in locally anesthetized, vagotomized cats which were immobilized with gallamine. When the alveolar CO2 tension is reduced, there is a decrease in phrenic discharge, as well as an increase of respiratory frequency, which may become as high as several cycles per second ("hypocapnic polypnea"). Diencephalic section (level of optic chiasma) results in a marked increase of phrenic discharge during hypocapnia; it is therefore concluded that forebrain structures may exert a tonic inhibitory effect on inspiratory discharge. While diencephalic section does not prevent hypocapnic polypnea, mesencephalic section (intercollicular level) eliminates the phenomenon or drastically reduces its extent; it is therefore concluded that at the posterior diencephalic and upper midbrain levels there are systems whose tonic activity tends to increase the respiratory frequency. In naturally breathing, midcollicular decerebrate cats, it was found that CO2 inhalation while the vagi are intact causes an increase of respiratory frequency, whereas after vagotomy it causes a decrease of frequency; thus, vagal afferent input results in reversal of the phenomenon of hypocapnic polypnea.

[A DIENCEPHALIC SYNDROME ASSOCIATED WITH A CEREBAL TUMOR IN AN INFANT]

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THE CONNEXIONS OF THE AMYGDALA

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