Chemoarchitectonics of the brainstem in infrared sensitive and nonsensitive snakes.

The crotaline snake Agkistrodon possesses infrared receptors, whereas the colubrid Elaphe quadrivirgata does not. We compared the histochemical activity of succinate dehydrogenase (SDH), monoamine oxidase (MAO), and acetylcholinesterase (AChE) in the brainstem of these 2 species, by the method of Nachlas et al. (1957), Glenner et al. (1957), and Koelle and Friedenwald (1949), respectively, and made the following observations. Visual system: The tectum opticum (TO) exhibited strong or moderate AChE and SDH activity in areas receiving retinal projections, i.e. the str. zonale (sz), str. fibrosum et griseum superficiale (sfgs), and narrow areas between small tight fasciculi of the tr. opticus. The sfgs was divided into 2 sublayers, a superficial and a deep, by the intensity of AChE activity. The deep sublayer of the sfgs and sfc of Agkistrodon were stained more strongly than other layers. Numerous fibers within the TO showed MAO activity. The entire sfgs of Agkistrodon was thinner than in Elaphe. The nucl. posterodorsalis showed moderate AChE, and weak SDH and MAO activity in Agkistrodon, but lack of AChE, weak SDH, and moderate MAO activity in Elaphe. Infrared system: This system was present only in Agkistrodon. The nucl. of the lateral descending trigeminal tract (dlV) and the nucl. reticularis caloris (rc) showed to moderate SDH activity in the main neuropil and/or perikarya. These nuclei were not conspicuous in AChE preparations. The marginal neuropil of the dlV had weak SDH, and moderate AChE and MAO activity. Common sensory trigeminal system: Moderate activity of the 3 enzymes was seen in the nucl. tr. descendens n. trigemini (dl). In the dorsomedial part of the nucl. interpolaris, the round limited portion was stained strongly for SDH and AChE. Cells of the nucl. tr. mesencephalicus n. trigemini showed strong SDH and AChE activity. Other regions: In Elaphe, there was strong to moderate AChE and SDH activity in the nucl. of the fasciculus longitudinalis medialis, nucl. centralis superior, raphe nuclei, and reticular nuclei, but only weak activity in Agkistrodon. We also found the following similarities in the 2 species. Strong to moderate AChE and SDH activity was observed in the motor nuclei of the cranial nerves, pretectal nuclei excepting the nucl. posterodorsalis, nucl. opticus basalis, and nucl. posterolateralis tegmentalis. Strong to moderate activity of the 3 enzymes together was detected in the nucl. interpeduncularis as found in other animals previously studied, and in the nucl. commissurae cornae dorsalis, nucl. cochlearis angularis, and the molecular and granular layer of the cerebellum.(ABSTRACT TRUNCATED AT 400 WORDS)