Deafferented Preparations Research Articles

Neural mechanism for generating and switching motor patterns of rhythmic movements of ovipositor valves in the cricket

In adult female crickets ( Gryllus bimaculatus), rhythmic movements of ovipositor valves are produced by contractions of a set of ovipositor muscles that mediate egg-laying behavior. Recordings from implanted wire electrodes in the ovipositor muscles of freely moving crickets revealed sequential changes in the temporal pattern of motor activity that corresponded to shifts between behavioral steps: penetration of the ovipositor into a substrate, deposition of eggs, and withdrawal of the ovipositor from the substrate. We aimed in this study to illustrate the neuronal organization producing these motor patterns and the pattern-switching mechanism during the behavioral sequence. Firstly, we obtained intracellular recordings in tethered preparations, and identified 12 types of interneurons that were involved in the rhythmic activity of the ovipositor muscles. These interneurons fell into two classes: ‘initiator interneurons’ in which excitation preceded the rhythmic contractions of ovipositor muscles, and ‘oscillator interneurons’ in which the rhythmic oscillation and spike bursting occurred in sync with the oviposition motor rhythm. One of the oscillator interneurons exhibited different depolarization patterns in the penetration and deposition motor rhythms. It is likely that some of the oscillator interneurons are involved in producing different oviposition motor patterns. Secondly, we analyzed oviposition motor patterns when the mecahnosensory hairs located on the inside surface of the dorsal ovipositor valves were removed. In deafferented preparations, the sequential change from deposition to withdrawal did not occur. Therefore, the switching from deposition pattern to withdrawal pattern is signaled by the hair sensilla that detect the passage of an egg just before it is expelled.

Specificity of Intramuscular Activation During Rhythms Produced by Spinal Patterning Systems in the In Vitro Neonatal Rat With Hindlimb Attached Preparation

In intact adult vertebrates, muscles can be activated with a high degree of specificity, so that even within a single traditionally defined muscle, groups of motor units can be differentially activated. Such differential activation might reflect detailed control by descending systems, potentially resulting from postnatal experience such that activation of motor units is precisely tailored to their mechanical actions. Here we examine the degree to which such specific activation can be seen in the rhythmic patterns produced by isolated spinal motor systems in neonates. We examined motor output produced by the in vitro neonatal rat spinal cord with hindlimb attached. We recorded the activity of different regions within the posterior portion of biceps femoris (BFp; i.e., excluding the anterior/vertebral head). We found that in the rhythms evoked by bath application of serotonin/N-methyl-d-aspartate (5-HT/NMDA), all regions of BFp were active during extension. However, the regions of BFp were activated in a specific sequence, with the activation of rostral regions consistently preceding those of more caudal regions in both afferented and deafferented preparations. In the rhythms evoked by cauda equina (CE) stimulation, rostral and middle regions of BFp remained active in extension, but the caudal region of BFp was usually active in flexion. Stimulation of L5 and S2 dorsal roots typically evoked rhythms with all regions of BFp active during extension; although the same rostral to caudal sequence of activation observed in 5-HT/NMDA evoked rhythms could also be observed in these rhythms, we also observed cases with reversed sequences, with activity proceeding from caudal to rostral. S2 dorsal root stimulation occasionally evoked rhythms with flexor activity in caudal BFp, similar to CE-evoked rhythms. Taken together, these results suggest a high degree of individuated control of muscles by spinal pattern generating networks, even at birth.

Exposure to heat shock affects thermosensitivity of the locust flight system.

The natural habitat of the migratory locust, Locusta migratoria, is likely to result in locusts being heat stressed during their normal adult life. It is known that locusts exhibit a heat-shock response: exposure to 45 degrees C for 3 h induces thermotolerance and the expression of heat-shock proteins. We investigated the effects of exposure to heat-shock conditions on the thermosensitivity of flight rhythm generation in tethered, intact animals and in deafferented preparations. Heat shock had no effect on wingbeat frequency measured at the start of flight sequences, nor did it affect the postimaginal maturation of this parameter. During sustained flight, heat shock slowed the characteristic asymptotic reduction of wingbeat frequency. Wingbeat frequency of heat-shocked animals was less sensitive to temperature in the range 24 degrees to 47 degrees C than that of control animals, and the upper temperature limit, above which flight rhythms could not be produced, was 6 degrees to 7 degrees C higher in heat-shocked animals. These results were mirrored in the response of deafferented preparations, indicating that modifications in the properties of the flight neuromuscular system were involved in mediating the response of the intact animal. We propose that exposure to heat shock had the adaptive consequences of reducing thermosensitivity of the neural circuits in the flight system and allowing them to operate at higher temperatures.

Rhythmic patterns in the thoracic nerve cord of the stick insect induced by pilocarpine

Bath application of the muscarinic agonist pilocarpine onto the deafferented stick insect thoracic nerve cord induced long-lasting rhythmic activity in leg motoneurones. Rhythmicity was induced at concentrations as low as 1x10(-4) mol l-1 pilocarpine. The most stable rhythms were reliably elicited at concentrations from 2x10(-3) mol l-1 to 5x10(-3) mol l-1. Rhythmicity could be completely abolished by application of atropine. The rhythm in antagonistic motoneurone pools of the three proximal leg joints, the subcoxal, the coxo-trochanteral (CT) and the femoro-tibial (FT), was strictly alternating. In the subcoxal motoneurones, the rhythm was characterised by the retractor burst duration being correlated with cycle period, whereas the protractor burst duration was almost independent of it. The cycle periods of the rhythms in the subcoxal and CT motoneurone pools were in a similar range for a given preparation. In contrast, the rhythm exhibited by motoneurones supplying the FT joint often had about half the duration. The pilocarpine-induced rhythm was generated independently in each hemiganglion. There was no strict intersegmental coupling, although the protractor motoneurone pools of the three thoracic ganglia tended to be active in phase. There was no stereotyped cycle-to-cycle coupling in the activities of the motoneurone pools of the subcoxal joint, the CT joint and the FT joint in an isolated mesothoracic ganglion. However, three distinct 'spontaneous, recurrent patterns' (SRPs) of motoneuronal activity were reliably generated. Within each pattern, there was strong coupling of the activity of the motoneurone pools. The SRPs resembled the motor output during step-phase transitions in walking: for example, the most often generated SRP (SRP1) was exclusively exhibited coincident with a burst of the fast depressor trochanteris motoneurone. During this burst, there was a switch from subcoxal protractor to retractor activity after a constant latency. The activity of the FT joint extensor motoneurones was strongly decreased during SRP1. SRP1 thus qualitatively resembled the motoneuronal activity during the transition from swing to stance of the middle legs in forward walking. Hence, we refer to SRPs as 'fictive step-phase transitions'. In intact, restrained animals, application of pilocarpine also induced alternating activity in antagonistic motoneurone pools supplying the proximal leg joints. However, there were marked differences from the deafferented preparation. For example, SRP1 was not generated in the latter situation. However, if the ipsilateral main leg nerve was cut, SRP1s reliably occurred. Our results on the rhythmicity in leg motoneurone pools of deafferented preparations demonstrate central coupling in the activity of the leg motoneurones that might be incorporated into the generation of locomotion in vivo.

Activity of the forewing stretch receptor in immature and mature adult locusts

Maturation of the flight system of Locusta migratoria occurs during the first two weeks following imaginal ecdysis. One aspect of maturation is an increase in the wingbeat frequency from about 13 Hz to about 23 Hz. We investigated physiological and anatomical mechanisms that may contribute to this process. The difference between the frequencies of the central flight rhythms of immature and mature deafferented preparations was not as great as that between the wingbeat frequencies of immature and mature intact animals. Results from static and dynamic wing elevation showed that the intensity of the forewing stretch receptor response to a given stimulus increased during maturation. The diameter of the main stretch receptor axon was larger and the conduction velocity of signals conveyed along the forewing stretch receptor and the dorsal longitudinal motoneuron was faster in mature than in immature animals. We conclude that during maturation of the flight system the forewing stretch receptor responds to wing elevation with a higher frequency signal that reaches the central circuitry faster. These findings are discussed in the context of a model that describes the influence of stretch receptor input on wingbeat frequency along with other potential mechanisms involved in flight maturation.

Multiple effects of an identified proprioceptor upon gastric pattern generation in spiny lobsters.

1. Using deafferented preparations of the stomatogastric nervous system of spiny lobsters (Panulirus interruptus), we stimulated the central soma of the Anterior Gastric Receptor neuron (AGR) and analyzed sensorimotor integration in the gastric central pattern generator during rhythm production. 2. Driving AGR to spike tonically at lower frequencies (10-20/s) accelerated the gastric rhythm, while higher frequencies (> or = 30/s) suppressed it. 3. Shorter spike trains in AGR evoked phase-dependent resetting of the gastric rhythm. Repetitive trains could entrain rhythms to both longer and shorter cycle periods. Some pattern-generating effects are consistent with effects upon the lateral gastric neuron, an influential member of the gastric mill network. 4. AGR affected the burst intensity of many of the gastric neurons in specific, complex ways. Some power-stroke motor neurons were excited because AGR activated excitatory, premotor interneurons (E cells). However, AGR also activated parallel, seemingly inhibitory inputs, whose mechanism remains unclear. Still other effects on motor neurons may be mediated partly by synaptic interactions within the network.

Degeneration of afferent neurons and long-term stability of the ventilatory central pattern generator in chronically deafferented crabs

1. The effects of chronic deafferentation, 3-180 days, are tested on the function and morphology of the crab (Carcinus maenas) ventilatory central pattern generator (CPGv). Almost all afferent axons are carried in the mixed sensory/motor levator nerve. The ability to speed the CPGv cycle rate by stimulating this nerve (Wilkens and DiCaprio 1994) decreases as the afferent neurons degenerate. Stimulation of the levator nerve eliminates motor units from the output even after 60 days of deafferentation, similar to the effects seen in acute preparations. 2. The 3 oval organ afferent axons of the levator nerve have central somata and survive scaphognathectomy. Impulses carried by these axons are known to inhibit the CPGv in acutely deafferented preparations and they are believed to be responsible for the persistent inhibition following small afferent degeneration seen here. 3. After 6 months of deafferentation the motor neuron collateral arborization densities within the thoracic ganglia are reduced, but all motor neurons appear to survive. These long-term deafferented CPGvs generate accurate motor patterns at similar rates to the control CPGv, but at reduced intraburst spike frequency. The crab CPGv is quite stable following chronic deafferentation.

Convergent force fields organized in the frog's spinal cord

Microstimulation of the gray matter of the frog's spinal cord was used to elicit motor responses. Force responses were recorded with the frog's ankle clamped while EMG activity was monitored. The collections of force patterns elicited at different leg configurations were summarized as force fields. These force fields showed convergence to an equilibrium point. The equilibrium paths were calculated from the force fields with the leg clamped. These paths predicted free limb motion in 75% of trials. The force fields were separated into active and prestimulation resting responses. The active force field responses had a fixed position equilibrium. These active force fields were modulated in amplitude over time, although the balance and orientations of forces in the pattern remained fixed. The active fields grouped into a few classes. These included both convergent and parallel fields. The convergent force fields (CFFS) could be observed in deafferented preparations. Motoneuron (MN) activity underlying the force fields was marked using sulforhodamine. The marked activity covered several segments. Several simulations and MN stimulations show that topography, limb geometry, and random activation could not account for the results. It is likely that propriospinal interneurons distribute the activity that underlies the responses observed here. Experiments showed that CFFs that resemble those elicited by microstimulation also underlie natural behaviors. The full variety of fields revealed by microstimulation was larger than the repertoire elicited by cutaneous stimulation. It was concluded that fixed-pattern force fields elicited in the spinal cord may be viewed as movement primitives. These force fields could form building blocks for more complex behaviors.

Mesothoracic interneurons involved in flight steering in the locust

1. 1. Twenty-eight interneurons with somata in the mesothoracic ganglion of the locust Locusta appear to be involved in steering in flight. All have their arborizations in the dorsal (flight) neuropil. All make directionally selective responses to visual, ocellar or wind stimuli corresponding to simulated deviations from course in flight. All are directly and/or indirectly postsynaptic to one or more sensory descending neurons (DNs) of the brain, which have been shown to produce steering behaviour when electrically stimulated. Convergence of DNs leads to complex responses by the interneurons. Some receive a variety of additional sensory information derived from thoracic receptors, especially wing proprioceptors and the ear. 2. 2. The membrane potentials of all these interneurons are modulated at flight frequency during fictive flight in deafferented preparations. Nineteen are depolarised in depressor phase (and/ or hyperpolarised in elevator phase); nine are depolarised in elevator phase (and/or hyperpolarised in depressor phase). The modulation derives in at least one case (neuron 016), and presumably in all, from synaptic drive from oscillator or oscillator-follower interneurons. None of the described cells, with the possible exception of IN 313, is thought to be part of the oscillator itself. 3. 3. The 28 ‘steering interneurons’ are characterised and named. Five (016, 035, 036, 302, 313) have been previously described in other contexts. Of these, the first 3 have been renamed; they were previously 116, 135 and 136 of Rowell and Pearson (1983). Four other previously named units are synonomized: 318 of Rowell and Pearson (1983) becomes 302 of Robertson and Pearson (1983), and 120 and 119 of Rowell and Pearson (1983), and 1AA of Elson (1987), all become 016. Two new modifications of the numbering system for locust interneurons are introduced. 4. 4. Five steering neurons are known to make monosynaptic, excitatory or inhibitory connections with flight motor neurons. Individual steering interneurons contribute between 25% and 10% of the total oscillatory drive to individual FMNs. 5. 5. The population of steering interneurons is the site of convergence of oscillator drive and sensory input prior to reaching the motor neuron: this allows sensory modulation of the strength and timing of drive to the individual motor neuron in the appropriate phase of the wing beat cycle, which is required for corrective steering. They are also a point at which the motor drive to the motor neuron is modified by proprioceptive reafference.

Reflex patterns in postganglionic vasoconstrictor neurons following chronic nerve lesions

Lesions of limb nerves in man may be associated with a variety of painful disorders with trophic changes described by the generic term ‘reflex sympathetic dystrophy’. Our hypothesis is that pain and trophic changes are produced by an abnormal discharge pattern in postganglionic neurons supplying the limb (see refs. 3,24). In relation to this hypothesis, reflex patterns in postganglionic vasoconstrictor neurons supplying the skin (CVC) and the skeletal muscle (MVC) of the cat hindlimb were investigated at various times after a peripheral nerve lesion had been produced. These reflex patterns were compared with those in animals without nerve lesions (control preparations). The following lesions were made; (a) cutting and ligating the superficial peroneal nerve (skin nerve) with subsequent neuroma formation, (b) suturing the central stump of the superficial peroneal nerve to the peripheral stumps of muscle branches of the deep peroneal nerve, (c) suturing the central stumps of muscle branches of the deep peroneal nerve to the peripheral stump of the superficial peroneal nerve, (d) cutting and resuturing the superficial peroneal nerve, (e) deafferentation of the whole hindlimb. The responses of vasoconstrictor neurons to stimulation of arterial chemoreceptors, arterial baroreceptors (cardiac rhythmicity of postganglionic activity) and cutaneous nociceptors were tested. In the animals with nerve lesions, the following groups of postganglionic vasoconstrictor neurons were analyzed: neurons projecting to the lesioned nerve, neurons projecting to hairy skin through an intact skin nerve (sural nerve) and neurons projecting to skeletal muscle through intact muscle nerves. (1) In control preparations without nerve lesions, MVC neurons were excited by stimulation of arterial chemoreceptors and cutaneous nociceptors and inhibited by stimulation of arterial baroreceptors. Most CVC neurons were inhibited by stimulation of chemoreceptors and nociceptors and weakly inhibited by stimulation of baroreceptors. (2) In animals with nerve lesions a and b, many CVC neurons in the lesioned nerves, as well as in the non-lesioned cutaneous nerve nearby, behaved in the same manner as MVC neurons. With respect to the control, this difference proved to be statistically significant. In preparations with lesions a, b and c, MVC neurons did not change their reflex patterns. (3) After nerve lesions d and e, no major changes of reflex patterns were observed in CVC and MVC neurons. The inhibitory influence of arterial baroreceptors on CVC activity decreased in deafferented preparations (lesion c). (4) The results indicate that lesions of cutaneous nerves of an extremity may lead to changes in the response pattern in CVC neurons to certain afferent stimuli, in the sense that this pattern becomes similar to that in MVC neurons.

Integration of nonphaselocked exteroceptive information in the control of rhythmic flight in the locust.

The integration of exteroceptive information in the flight control system of the locust was studied by determining the cellular basis of ocellar- (simple eye) mediated control of flight. Neural interactions that transform phase-independent sensory input into phase-specific motor output were characterized. Ocellar information about course deviations during flight was conveyed to the segmental thoracic ganglia by three pairs of large fast multimodal descending neurons. These made connections with thoracic motoneurons directly, via short-latency mono-or disynaptic pathways, and indirectly, via a population of intercalated thoracic interneurons. The synaptic potentials caused in the motoneurons by the direct pathway occurred at short latency and were adequate for summation with other types of sensory input. However, the strength of the synaptic effects of this pathway was weak compared with the central flight oscillator drive to the same motoneurons. In contrast, synaptic potentials evoked by the descending neurons in the thoracic interneurons were often large and brought these cells close to threshold. In turn, these interneurons always had stronger synaptic effects on postsynaptic flight motoneurons than did the descending neurons alone. We conclude that the indirect interneuronal pathway is more powerful in its effects on motoneurons than the direct pathway. Premotor thoracic interneurons, which received ocellar input appropriate for a role in correctional steering, were also rhythmically modulated during flight motor activity in phase with either depressor or elevator motoneurons. This phasic modulatory drive occurred in deafferented preparations, indicating that its source is the central oscillator for flight. Presentation of ocellar stimulation during flight motor activity showed that the central oscillatory modulation of the thoracic interneurons gated the transmission of sensory information through these interneurons. Ocellar-mediated postsynaptic potentials influenced the firing of thoracic interneurons only if they arrived during the proper phase of rhythmic drive. Thus the transmission of ocellar information from interneuron to motor neuron is possible only during appropriate phases of the flight cycle.

Neural circuits in the flight system of the locust.

Circuitry in the flight system of the locust, Locusta migratoria, was investigated by use of intracellular recording and staining techniques. Neuronal connections were established by recording simultaneously from neuropile segments of pairs of identified interneurons. Brief depolarizing current pulses delivered to interneurons 301 and 501 reset the flight rhythm in a phase-dependent manner, thus establishing the importance of these neurons in rhythm generation. Interneuron 301 was found to make a strong delayed excitatory connection with 501 and to receive a short-latency inhibitory connection from 501. The circuit formed by 301 and 501 appears suited for promoting rhythmicity in the flight system. The delayed excitatory potential recorded in 501 following each spike of 301 was reversed by hyperpolarizing 501. This potential and short-latency inhibitory postsynaptic potentials from 301 to other interneurons were blocked with the application of picrotoxin. We conclude that the delayed excitation is produced via a disynaptic pathway from 301 to 501, with 301 inhibiting in a graded manner the tonic release of transmitter from one or more unidentified intercalated neurons. Interconnections between the 301-501 circuit and other identified interneurons were discovered. This circuitry can account for two features of the flight motor pattern recorded in deafferented preparations. These features are the constant-latency relationship between depolarizations in elevator and depressor motoneurons and the relatively constant duration of depressor motoneuron bursts. The locust flight system shares general features with other described rhythm-generating systems. These include the occurrence of graded interactions, the probability of multiple oscillatory mechanisms, and a predominance of inhibitory connections. Its uniqueness lies in the way that components and processes are assembled and operate.

Patterns of synaptic input to identified flight motoneurons in the locust

1. We examined the pattern of synaptic input to identified flight motoneurons of the locust,Locusta migratoria. The preparation we used was one in which rhythmic motor activity resembling flight activity could be generated following removal of all sensory input from wing receptors. Intracellular recordings were made from the main neuropil processes of all the 17 different types of fast motoneurons in the meso- and metathoracic ganglia which innervate the main flight muscles. Motoneurons were identified anatomically by intracellular staining with Lucifer yellow following recording. 2. The pattern of synaptic input was similar in all elevator motoneurons (4 different types in each of the two ganglia). Three distinct components were observed in the profile of synaptic activity in these motoneurons. The first was a relatively slow depolarization beginning immediately after the end of a depolarization in depressor motoneurons, the second was a rapid depolarization which began at a variable interval after the beginning of the initial slow depolarization, and the third was a rapid repolarization occurring in-phase with depressor depolarizations. The similarity of synaptic input to elevator motoneurons prevented the use of physiological criteria for the identification of individual elevator motoneurons. 3. Unlike the elevators, the depressor motoneurons do not form a homogeneous group with regard to the pattern of centrally derived synaptic input. Different patterns of input were observed in different depressor motoneurons, including differences in input to homologous motoneurons in the meso- and metathoracic ganglia. The most obvious difference between the profiles of synaptic input to elevator and depressor motoneurons was that the depolarizations in the latter consisted of only a single component, the duration of which increased relatively slowly with increases in cycle time. Knowledge of the recording site within a ganglion and the pattern of synaptic input allowed depressor motoneurons to be identified individually. 4. Simultaneous recordings from an elevator and a depressor motoneuron within the same ganglion showed that the synaptic input to the two groups of motoneurons is not symmetrically timed. Each depolarization in depressor motoneurons began immediately following the end of a rapid depolarization in elevators, but the beginning of the rapid depolarizations in elevators was delayed following the end of each depressor depolarization by an amount depending on cycle time. A single depressor depolarization never occurred in the absence of a preceding rapid elevator depolarization. We conclude that the basic unit of activity in the central oscillator is an elevator followed by a depressor depolarization sequence. 5. Simultaneous recordings from homologous motoneurons in the meso- and metathoracic ganglia of deafferented preparations revealed that the depolarizations in elevator motoneurons in the two ganglia were in-phase. In depressors, however, the depolarizations in hindwing motoneurons led those in homologous forewing motoneurons by 5 to 15 ms indicating that central processes are partly, but not completely, responsible for establishing the relative timing of fore and hind wing movements in normal flight. This basic difference in the intersegmental driving of elevator and depressor motoneurons in deafferented preparations was confirmed in electromyographic recordings from homologous fore- and hindwing muscles.

Neural organization of peptide-activated ecdysis behaviors during the metamorphosis ofManduca sexta

1. At the culmination of each molt, insects shed their old cuticle by a behavior called ecdysis, which generally involves rhythmic peristaltic body movements. We have compared the abdominal peristalsis behaviors produced by the tobacco hornworm,Manduca sexta, during larval-larval molts (‘larval ecdysis’) and at the larval-pupal molt (‘pupal ecdysis’), to see whether the morphological changes during metamorphosis were accompanied by alterations in the motor patterns. 2. At larval ecdysis, caterpillars shed their old cuticle by means of rhythmic peristaltic contractions which run anteriorly along the body, accompanied by coordinated retractions and extensions of the abdominal prolegs (Fig. 2). During the larval-pupal transformation the prolegs are lost, so that at pupal ecdysis the cuticle is shed by peristalsis alone (Fig. 1). 3. Cinematographic analysis of ecdysing larvae and pupae revealed that the peristaltic movements resulted from each abdominal segment being sequentially pulled forward and partially telescoped into the next anterior segment, due to the contraction of intersegmental muscles (ISMs) in the more anterior segment. Despite the marked changes in body morphology which occurred during the larval-pupal transformation, the pattern of the peristaltic contractions produced at larval and pupal ecdysis was the same (Table 1). 4. The neural basis of these behaviors was investigated in semi-intact, deafferented preparations which produced ecdysis motor patterns in response to a peptide hormone, eclosion hormone (EH), which is the normal blood-borne trigger for ecdysis (Fig. 3). The motoneurons which generated the peristaltic motor patterns in larvae and pupae were identified by recording extracellularly from various nerve branches (Figs. 4, 5, 6, 8) and intracellularly from neuronal somata (Figs. 7, 9). 5. The pattern of the motoneuron bursts was the same during both larval and pupal ecdysis (Table 2). The only apparent difference at the two stages was that pupae exhibited a lower level of tonic background motor activity than did larvae (e.g., Figs. 4, 8). 6. Thus, both behavioral and electrophysiological data indicated that the pattern-generating circuitry underlying abdominal peristalsis remained stable during the larval-pupal transformation. In contrast, the loss of the prolegs at pupation and their consequent absence from pupal ecdysis behavior did suggest a possible stage-specific change in the neural circuitry; this possibility is investigated in an accompanying paper (Weeks and Truman 1984).

Lack of sprouting and its presence after lesions of the cat spinal cord

Degeneration methods were used to study the dorsal root and descending projections after chronic partial denervation of adult cat spinal cord. Conventional mapping methods were used, supplemented in some cases by densitometric measurements of the amounts of degeneration present. The amount of shrinkage of spinal gray matter in some sections was estimated by planimetric measurement. Two preparations were used: (1) partial unilateral rhizotomy in which all dorsal roots caudal to T4 were cut except L6 (spared root preparation); (2) complete unilateral deafferentation. The projection of L6 dorsal roots was examined in spared root preparations. T13 dorsal root projections were examined in deafferented preparations in which T13 was the lowest remaining root. The projection of descending systems was mapped in spared root and deafferented preparations. The spared root displayed an increased projection in the lateral portion of the dorsal horn, in the zona intermedia. Clarke's nucleus and in the base and reticular zone of nucleus gracilis. The lowest remaining root (T13) increased its projection to laminae VII and VIII and to the base and reticular zone of nucleus gracilis. In all cases, when an increased projection resulted from prior denervation, the increase never exceeded the boundaries of the normal projection. No sprouting was observed in those regions with the strictest topographical organization, the cell nests of nucleus gracilis or lamina IX of the spinal cord, even though these regions were partially denervated by the chronic lesions. Descending projections were increased on the experimental side of deafferented preparations 12 but not of spared root preparations, suggesting that the presence of the spared root may prevent sprouting by descending systems. Because measurements of gray matter indicated that maximal sprouting occurred in segments showing least shrinkage (sprouting of L6 spared root into L6 segment), in this case shrinkage cannot account for the increased density of degeneration. These results suggest that certain conditions are important for the regulation of sprouting in the adult CNS. Firstly, sprouting is limited by a requirement for proximity and/or overlap. Secondly, the strictness of topographical localization within a particular region may limit the likelihood of sprouting into that region. Finally, a competitive or hierarchical relationship among the remaining systems may modify the capacity of a particular system to sprout.

Central excitation of cockroach giant interneurons during walking

Extracellular recordings from the ventral nerve cord of suspended or free-walking cockroaches (Periplaneta americana) reveal that a number of the giant interneurons in the cord become active during locomotion. We have studied this walking-activated excitation of these interneurons. 1. The initiation of firing of the giants as walking begins and the cessation of their activity as it stops is extremely rapid (Fig. 1), occuring within approximately 10 ms in many instances. 2. The average frequency of firing of the excited giants is higher during faster steps than during slower ones—i.e., is positively correlatd with speed of walking. This relationship is weakened by severing the ventral nerve cord in the abdomen (Figs. 2, 3). 3. Pinned-out, deafferented preparations may be induced to produce rhythmic activity in leg motoneurons similar to that observed during walking. One or more giant interneurons is excited during such rhythmic activity (Fig. 4), suggesting that sensory input from the moving legs during locomotion is not the main source of the excitatory signals. All this evidence supports the suggestion (Delcomyn, 1977) that the excited giants are driven by corollary discharge from the locomotor centers in the thorax. 4. Comparisons of the amplitudes of action potentials of those neurons active during spontaneous walking (Fig. 5) and those responding to puffs of air during rest (Fig. 6) suggested that not all the giants were active during walking. Intracellular recordings from individual giants confirmed this, revealing that only the three smaller, dorsal giants were excited (Fig. 7), while the three largest, ventral ones were not (Fig. 8). 5. The possible function of corollary discharge to the dorsal giants and the subsequent excitation of these interneurons during walking is discussed. Two possible functions are considered: 1) to keep the insect responsive to air disturbances during walking, and 2) to provide a general excitatory input to the central nervous system necessary to keep central excitatory state high during walking.

Effects of sytemic hypoxia and hypercapnia on cutaneous and muscle vasoconstrictor neurones to the cat's hindlimb.

1. Reactions of cutaneous and muscle vasoconstrictor neurones to the hindlimb on systemic hypoxia and systemic hypercapnia were investigated in chloralose anaesthetized cats. Mainly four types of preparations were used: brain intact and decrebrate (pontomedullary) animals with and without carotid sinus (CSN) and vagal nerves (VN). 2. In brain intact animals with intact CSN and VN most cutaneous vasoconstrictor neurones were depressed and most muscle vasoconstrictor neurones were excited during systemic hypoxia and hypercapnia. The responses to hypercapnia were smaller than those to hypoxia. 3. In brain intact deafferented animals and in decerebrate animals with and without intact CSN and VN systemic hypoxia and hypercapnia induced excitation in both cutaneous and muscle vasoconstrictor neurones. The responses to hypoxia were significantly smaller in deafferented preparations when compared to those in preparations with intact CSN and VN. Furthermore in muscle vasoconstrictor neurones the size of the responses was not significantly different in decerebrate preparations from that in brain intact preparations. 4. These results indicate a distinct neuronal organization of the chemoreceptor reflexes in the vasoconstrictor systems in the brain stem. Suprapontine brain structures are most important for producing the inhibition of the cutaneous vasoconstrictor neurones during hypoxia and hypercapnia.

Functional circuitry of the goldfish cerebellum

1. The basic circuitry of the cerebellum of goldfish is similar to that in other vertebrates but with several special features. Deep nuclei are lacking and the axons of approximately 80% of Purkinje cells leave the cerebellum. 2. Responses of granule cells indicate much convergence of mossy fiber inputs. Some Purkinje cells give single simple spikes, others trains of spikes in response to mossy fiber or parallel fiber stimulation. 3. Inhibitory interneurons—stellate and Golgi cells—are characterized by high-frequency, ongoing spikes. Parallel fibers activate interneurons which inhibit granule cell responses to mossy input and which also inhibit Purkinje cells as indicated by IPSP's, interruption of spontaneity and of responses via mossy fiber-granule cell input. 4. Peduncle stimulation in deafferented preparations revealed Purkinje cell collateral inhibition of other Purkinje cells and of Golgi cells. 5. Climbing fiber stimulation elicits complex responses in Purkinje cells, often followed by inhibition and, in some cells, a late second excitatory response.

Nervous Mechanisms Underlying Intersegmental Co-Ordination of Leg Movements During Walking in the Cockroach

ABSTRACT The activity in identical motoneurones innervating leg muscles of the three thoracic segments of the cockroach has been recorded in (a) normal walking animals, (b) walking animals after lesions to the nervous system and/or amputation of the mesothoracic legs, and (c) restrained de-afferented preparations. The phase of levator motoneurone burst activity of the mesothoracic leg in the metathoracic cycle is almost 0 · 5 for all walking speeds above 2 steps/sec, confirming that a tripod gait is used at all but the slowest speeds. The burst-generating systems in each segment are centrally coupled because in de-afferented preparations there is a tendency for the bursts in the mesothoracic segment to begin near the end of the metathoracic bursts, and vice versa. Sensory input from leg receptors is also important in co-ordinating stepping movements of the different legs since (a) there are some differences in motoneurone activity of de-afferented and walking preparations, and (b) amputation of the mesothoracic legs at the trochanter leads to an immediate change in the co-ordination of the remaining four legs. It is proposed that two mechanisms are important in co-ordinating leg movements in a slow walking cockroach (a) mutual inhibition between levator burst-generating systems in adjacent ipsilateral legs, and (b) an inhibitory reflex pathway from the campaniform sensilla of the trochanter to the burst-generating system of each leg. The second of these two mechanisms may become less important as the walking speed increases.

Central Programming and Reflex Control of Walking in the Cockroach

ABSTRACT The activity in identified motor units supplying the coxal levator and depressor muscles of the cockroach have been recorded in intact freely walking animals and in preparations after removal of all sensory input from leg receptors. Reciprocal activity in levator and depressor motoneurones can be evoked, or occurs spontaneously, in the partially de-afferented preparations, thus indicating the existence of a central locomotory rhythm generator. The reciprocal activity patterns recorded in the same motoneurones in intact freely moving animals are not identical to those recorded in partially de-afferented preparations. Thus, the production of normal rhythmic leg movements depends to some extent on sensory input from leg receptors, this input probably exerting tonic and phasic effects on the central rhythm generator. An increase in the resistance to leg retraction during normal walking results in an increase in discharge rate of the levator and depressor motoneurones. This observation further demonstrates that rhythmic leg movements are not exclusively centrally controlled. The receptors responsible for this reflex effect are probably the trochanteral campaniform sensilla.