Anne Bekoff

Patterns of muscle activity during different behaviors in chicks: implications for neural control.

The large behavioral repertoire that spans the embryonic and postembryonic stages of development make chicks an ideal system for identifying patterns of muscle activity that are common to different behaviors and those that are behavior-specific. The main goal of this work was to identify the similar and dissimilar aspects of the recruitment patterns and the regulation of muscle activity during three distinct postembryonic behaviors: walking, swimming and airstepping. We identified two synergies that were common to each of these behaviors. The synergies were not disrupted by the absence of FT1 activity in airstepping. Within each synergy the recruitment time, recruitment order and duration of activity were not rigid, but varied according to the context-specific resistance that the leg encountered. Unlike the other muscles, FT2 activity was not recruited as part of the same synergy in each behavior. When weight-bearing contact with the substrate did not occur, as in swimming and airstepping, as well as in walking in chicks with deafferented legs, FT2 activity was not recruited as part of either synergy, but was recruited during the time between them. Although not identical, embryonic motility and hatching motor pattern both show the two synergies described for the postembryonic behaviors. Like the latter behaviors, the synergies tolerated the absence of activity from specific muscles. Thus, we suggest that the CNS produces different behaviors using many of the same muscles by organizing the patterned activity around two common synergies while permitting the different muscles that participate in a synergy to be modified in tandem or on an individual basis. Furthermore, the common synergies are established early during prenatal development in chicks.

Enzyme Activities in Muscles of Seasonally Acclimatized House Finches

Members of the avian subfamily Carduelinae have served as subjects of numerous investigations on adaptations of small birds to cold winters (Salt, 1952; Dawson and Tordoff, 1964; West, 1972; Dawson and Carey, 1976; Carey et al. 1978; Weathers et al. 1980; Marsh et al. 1984; Reinertsen, 1986; Yacoe and Dawson, 1983; and others). These birds, including goldfinches, pine siskins, house finches, grosbeaks, crossbills, and redpolls, are particularly well suited for such study because of their principally northern distribution and small body sizes. Their success in cold climates appears to be linked in part to a type of metabolic acclimatization, involving enhanced capabilities for sustained elevated production of heat for prolonged periods (Dawson and Carey, 1976; Dawson et al. 1983a, b; Dawson and Marsh, 1988).

Spontaneous embryonic motility: an enduring legacy.

This chapter addresses the influential contributions Viktor Hamburger has made to our understanding of embryonic motor behavior. With his classic review, published in 1963, Viktor Hamburger opened up the field of embryonic motor behavior, which had lain almost completely dormant for many years. He focused his observations and experimental studies on the spontaneously generated embryonic movements rather than on reflex responses. As a result, he and his colleagues firmly established the central generation of embryonic motility as a basic component of embryonic behavior in chicks. These studies were also extended to rat fetuses, showing that similar principles apply to mammalian fetuses. All of us who have followed after him owe Viktor Hamburger an enormous debt of gratitude for his pioneering work.

Neural control of hatching: Role of neck position in turning on hatching leg movements in post-hatching chicks

Summary1.A previous study showed that the pattern generating circuit for the leg movements of hatching remains functional in post-hatching chicks and can be turned on by folding chicks into the hatching position and placing them in glass eggs (Bekoff and Kauer 1980). The goal of the present study was to determine what conditions are both sufficient and necessary to turn on this pattern generator in posthatching chicks.2.In preliminary experiments, 0- to 2-day old chicks were placed in glass eggs and then either legs or head were selectively released while the rest of the body was kept restrained in the hatching position. Results of these experiments suggested that head and/ or neck position was important in turning on the leg motor output pattern typical of hatching.3.To further clarify this issue, 0- to 2-day old chicks were suspended by a ring attached to the midthoracic region of the back. Various body parts could then be selectively and independently immobilized in specific positions. Restraining the chick in any way was sufficient to turn on periodic episodes of leg movements. The inter-episode intervals and episode durations approached, but were usually somewhat longer than, those of hatching (Table 2).4.However, restraining the neck by bending it tightly to the right or to the left was the only manipulation we could identify that turned on periodic episodes involving a synchronous pattern of interlimb coordination (Fig. 2). This pattern has been shown to be typical of hatching (Bekoff and Kauer, submitted). Therefore we conclude that bending the neck to the right or to the left is both sufficient and necessary to turn on the pattern generator for the leg movements of hatching in post-hatching chicks.

Pyridoxine treatment alters embryonic motility in chicks: Implications for the role of proprioception.

Somatosensory feedback is important for the modulation of normal locomotion in adult animals, but we do not have a good understanding of when somatosensory information is first used to modulate motility during embryogenesis or how somatosensation is first used to regulate motor output. We used pyridoxine administration (vitamin B6 ), which is known to mostly kill proprioceptive neurons in adult mammals and embryonic chicks, to explore the role of proprioceptive feedback during early embryonic motility in the chick. Injection of pyridoxine on embryonic day 7 (E7) and E8 reduced the amplitude of leg movements recorded on E9 and the number of large, healthy neurons in the ventral-lateral portion of the DRGs. We conclude that proprioception is initially used during embryogenesis to modulate the strength of motor output, but that it is not incorporated into other aspects of pattern generation until later in development as poly-synaptic pathways develop.