Functional subdivision of the venom gland musculature and the regulation of venom expulsion in rattlesnakes

Abstract

A combination of histology, whole muscle force physiology, glycogen depletion, and venom expulsion analyses using transonic probes to measure venom flow and fluid pressure transducers to measure venom pressure was performed on the m. compressor glandulae and m. pterygoideus glandulae. The m. pterygoideus glandulae has less than one‐third the cross‐sectional area of the m. compressor glandulae, and produces approximately one‐fifth the total twitch and tetanic force; however, in situ surface stimulation of the muscle produces venom flow and pressure levels that are similar to those produced by the m. compressor glandulae. The similarity in venom output following stimulation reflects in part the functional role of the larger m. compressor glandulae in jaw adduction, but also the functional subdivisions within this muscle. The m. compressor glandulae is divided into a series of columnar fascicles that run from the surface of the muscle to the venom gland. The combined results of clearing and staining and glycogen depletion studies suggest that these fascicles may represent functional compartments. Identical stimulations applied to different regions of the m. compressor glandulae result in up to a six‐fold difference in venom expulsion. This functional specialization may play a role in the regulation of venom flow during offensive and defensive strikes. J. Morphol. 246:249–259, 2000. © 2000 Wiley‐Liss, Inc.

Mechanisms controlling venom expulsion in the western diamondback rattlesnake, Crotalus atrox

“…4). This fatigue profile is consistent with what was observed in a previous study (Young et al, 2000). The fatigue of the Compressor Glandulae informed and dictated the experimental procedures used in this study.…”

Mechanisms controlling venom expulsion in the western diamondback rattlesnake, Crotalus atrox

“…4). This fatigue profile is consistent with what was observed in a previous study (Young et al, 2000). The fatigue of the Compressor Glandulae informed and dictated the experimental procedures used in this study.…”

The buccal buckle: the functional morphology of venom spitting in cobras

“…The similarity between our findings and the earlier experimental study of the viperid Crotalus (principally Young et al, 2000Young et al, , 2001a suggests functional convergence between these two lineages.…”

“…Rosenberg (1967) detailed the intra-glandular pressure model for venom injection in snakes, which described the functional relationship between contraction of the extrinsic venom gland musculature and venom expulsion. Key aspects of this model were supported by experimental studies of venom expulsion in Crotalus (Young et al, 2000), and by the results of the present study, where contraction of the extrinsic venom gland muscle (the AMES), either voluntarily by the cobra or through artificial stimulation, led to increases in venom pressure. Recently, Young et al (2002) developed a refined and expanded model for venom expulsion, termed the pressure-balance model.…”

Mechanics of venom expulsion in Crotalus, with special reference to the role of the fang sheath

“…6A) or venom gland (data not shown), include a negative pressure component, indicating that the venom gland is the source of this pressure. Rosenberg (1967) detailed the intraglandular pressure hypothesis that argues that external muscle forces increase the fluid pressure within the venom gland and cause venom to flow out the venom duct; this link between muscle contractile force and venom flow was recently demonstrated experimentally (Young et al, 2000). The negative pressure and flow obtained in this study appear to arise from expansion of the venom gland after contraction of the compressor glandulae or pterygoideus glandulae.…”

“…To allow maximal range of motion, the PE tubing made a U-bend in the snake's esophagus and was then connected to a PT300 pressure transducer (GRASS Instruments). With continuous stimulation (1 msec duration, 50 pps) applied to the dorsomedial surface (Young et al, 2000) of the compressor glandulae (S88 Stimulator, GRASS Instruments), the fang was erected by manual pressure applied to the compound-pterygoid joint. The output of the pressure transducer was amplified (P122 amplifier, GRASS Instruments) before being digitally converted and collected by the data acquisition system, as described above.…”

Mechanisms controlling venom expulsion in the western diamondback rattlesnake, Crotalus atrox

“…4). This fatigue profile is consistent with what was observed in a previous study (Young et al, 2000). The fatigue of the Compressor Glandulae informed and dictated the experimental procedures used in this study.…”

The buccal buckle: the functional morphology of venom spitting in cobras

“…The similarity between our findings and the earlier experimental study of the viperid Crotalus (principally Young et al, 2000Young et al, , 2001a suggests functional convergence between these two lineages.…”

“…Rosenberg (1967) detailed the intra-glandular pressure model for venom injection in snakes, which described the functional relationship between contraction of the extrinsic venom gland musculature and venom expulsion. Key aspects of this model were supported by experimental studies of venom expulsion in Crotalus (Young et al, 2000), and by the results of the present study, where contraction of the extrinsic venom gland muscle (the AMES), either voluntarily by the cobra or through artificial stimulation, led to increases in venom pressure. Recently, Young et al (2002) developed a refined and expanded model for venom expulsion, termed the pressure-balance model.…”

Mechanics of venom expulsion in Crotalus, with special reference to the role of the fang sheath

“…6A) or venom gland (data not shown), include a negative pressure component, indicating that the venom gland is the source of this pressure. Rosenberg (1967) detailed the intraglandular pressure hypothesis that argues that external muscle forces increase the fluid pressure within the venom gland and cause venom to flow out the venom duct; this link between muscle contractile force and venom flow was recently demonstrated experimentally (Young et al, 2000). The negative pressure and flow obtained in this study appear to arise from expansion of the venom gland after contraction of the compressor glandulae or pterygoideus glandulae.…”

“…To allow maximal range of motion, the PE tubing made a U-bend in the snake's esophagus and was then connected to a PT300 pressure transducer (GRASS Instruments). With continuous stimulation (1 msec duration, 50 pps) applied to the dorsomedial surface (Young et al, 2000) of the compressor glandulae (S88 Stimulator, GRASS Instruments), the fang was erected by manual pressure applied to the compound-pterygoid joint. The output of the pressure transducer was amplified (P122 amplifier, GRASS Instruments) before being digitally converted and collected by the data acquisition system, as described above.…”

Mechanisms controlling venom expulsion in the western diamondback rattlesnake, Crotalus atrox

“…4). This fatigue profile is consistent with what was observed in a previous study (Young et al, 2000). The fatigue of the Compressor Glandulae informed and dictated the experimental procedures used in this study.…”

The buccal buckle: the functional morphology of venom spitting in cobras

“…The similarity between our findings and the earlier experimental study of the viperid Crotalus (principally Young et al, 2000Young et al, , 2001a suggests functional convergence between these two lineages.…”

“…Rosenberg (1967) detailed the intra-glandular pressure model for venom injection in snakes, which described the functional relationship between contraction of the extrinsic venom gland musculature and venom expulsion. Key aspects of this model were supported by experimental studies of venom expulsion in Crotalus (Young et al, 2000), and by the results of the present study, where contraction of the extrinsic venom gland muscle (the AMES), either voluntarily by the cobra or through artificial stimulation, led to increases in venom pressure. Recently, Young et al (2002) developed a refined and expanded model for venom expulsion, termed the pressure-balance model.…”

Mechanics of venom expulsion in Crotalus, with special reference to the role of the fang sheath

“…6A) or venom gland (data not shown), include a negative pressure component, indicating that the venom gland is the source of this pressure. Rosenberg (1967) detailed the intraglandular pressure hypothesis that argues that external muscle forces increase the fluid pressure within the venom gland and cause venom to flow out the venom duct; this link between muscle contractile force and venom flow was recently demonstrated experimentally (Young et al, 2000). The negative pressure and flow obtained in this study appear to arise from expansion of the venom gland after contraction of the compressor glandulae or pterygoideus glandulae.…”

“…To allow maximal range of motion, the PE tubing made a U-bend in the snake's esophagus and was then connected to a PT300 pressure transducer (GRASS Instruments). With continuous stimulation (1 msec duration, 50 pps) applied to the dorsomedial surface (Young et al, 2000) of the compressor glandulae (S88 Stimulator, GRASS Instruments), the fang was erected by manual pressure applied to the compound-pterygoid joint. The output of the pressure transducer was amplified (P122 amplifier, GRASS Instruments) before being digitally converted and collected by the data acquisition system, as described above.…”