Dual pathways for tactile sensory information to thoracic interneurons in the cockroach

The escape system of the American cockroach is both fast and directional. In response to wind stimulation both of these characteristics are largely due to the properties of the ventral giant interneurons (vGIs), which conduct sensory information from the cerci on the rear of the animal to type A thoracic interneurons (TI_As) in the thoracic ganglia. The cockroach also escapes from tactile stimuli, and although vGIs are not involved in tactile-mediated escapes, the same thoracic interneurons process tactile sensory information. The response of TI_As to tactile information is typically biphasic. A rapid initial depolarization is followed by a longer latency depolarization that encodes most if not all of the directional information in the tactile stimulus. We report here that the biphasic response of TI_As to tactile stimulation is caused by two separate conducting pathways from the point of stimulation to the thoracic ganglia. Phase 1 is generated by mechanical conduction along the animal's body cuticle or other physical structures. It cannot be eliminated by complete lesion of the nerve cord, and it is not evoked in response to electrical stimulation of abdominal nerves that contain the axons of sensory receptors in abdominal segments. However, it can be eliminated by lesioning the abdominal nerve cord and nerve 7 of the metathoracic ganglion together, suggesting that the relevant sensory structures send axons in nerve 7 and abdominal nerves of anterior abdominal ganglia. Phase 2 of the TI_As tactile response is generated by a typical neural pathway that includes mechanoreceptors in each abdominal segment, which project to interneurons with axons in either abdominal connective. Those interneurons with inputs from receptors that are ipsilateral to their axon have a greater influence on TI_As than those that receive inputs from the contralateral side. The phase 1 response has an important role in reducing initiation time for the escape response. Animals in which the phase 2 pathway has been eliminated by lesion of the abdominal nerve cord are still capable of generating a partial startle response with a typically short latency even when stimulated posterior to the lesion. © 1995 John Wiley & Sons, Inc.     

Characterization of tactile-sensitive interneurons in the abdominal ganglia of the cockroach,Periplaneta americana

Tactile stimulation of an insect's abdomen evokes various behaviors including grooming and vigorous escape responses. We tested a sample of 37 tactile-sensitive abdominal interneurons for various morphological and physiological characteristics, including their ability to excite thoracic interneurons that are known to integrate wind information conducted by giant interneurons in the classical escape response. The results suggest that abdominal tactile-sensitive interneurons are heterogeneous both in anatomical and physiological properties. In general, these cells are very small interganglionic interneurons that respond to tactile stimulation at more than one abdominal segment. However, the larger population contained virtually all types of cells. Some projected anteriorly, others posteriorly, and still others projected in both directions. For most cells, the soma was on the side opposite to their axons, but in 24% of the cells it was on the same side. Patterns of dendritic arbors also varied among cells. However, tactile sensitivity was in general consistent with the morphological bias noted in dendritic branch patterns. We were able to document the existence of tactile abdominal interneurons that connect directly to thoracic interneurons involved in escape (TI_As). However, instances of demonstrated connectivity were rare. One cell that did show connectivity (AI652) was characterized in detail, and its properties were appropriate for conducting tactile signals in a directional escape system. The dendritic arbors were biased to the side that was ipsilateral to the cell's soma and axon. As a result, this cell's abdominal inputs and thoracic outputs are on the same side. This pattern is appropriate for generating the sensory fields recorded previously in TI_As. Its axon was located in the ventral median tract, which should bring it close to the integrating region of the TI_As. © 1998 John Wiley & Sons, Inc. J Neurobiol 34: 227–241, 1998     

Parallel motor pathways from thoracic interneurons of the ventral giant interneurons system of the cockroach,Periplaneta americana

The data described here complete the principal components of the cockroach wind-mediated escape circuit form cercal afferents to leg motor neurons. It was previously known that the cercal afferents excite ventral giant interneurons which then conduct information on wind stimuli to thoracic ganglia. The ventral giant interneurons connect to a large population of interneurons in the thoracic ganglia which, in turn, are capable of exciting motor neurons that control leg movements. Thoracic interneurons that receive constant short latency inputs from ventral giant interneurons have been referred to as type A thoracic interneurons (TI_As). In this paper, we demonstrate that the motor response of TI_As occurs in adjacent ganglia as well as in the ganglion of origin for the TI_A. We then describe the pathway from TI_As to motor neurons in both ganglia. Our observations reveal complex interactions between thoracic interneurons and leg motor neurons. Two parallel pathways exist. TI_As excite leg motor neurons directly and via local interneurons. Latency and amplitude of post-synaptic potentials (PSPs) in motor neurons and local interneurons either in the ganglion of origin or in adjacent ganglia are all similar. However, the sign of the responses recorded in local interneurons (LI) and motor neurons varies according to the TI_A subpopulation based on the location of their cell bodies. One group, the dorsal posterior group, (DPGs) has dorsal cell bodies, whereas the other group, the ventral median cells, (VMC) has ventral cell bodies. All DPG interneurons either excited postsynaptic cells or failed to show any connection at all. In contrast, all VMC interneurons either inhibited postsynaptic cells or failed to show any connection. It appears that the TI_As utilize directional wind information from the ventral giant interneurons to make a decision on the optimal direction of escape. The output connections, which project not only to cells within the ganglion of origin but also to adjacent ganglia and perhaps beyond, could allow this decision to be made throughout the thoracic ganglia as a single unit. However, nothing in these connections indicates a mechanism for making appropriate coordinated leg movements. Because each pair of legs plays a unique role in the turn, this coordination should be controlled by circuits didicated to each leg. We suggest that this is accomplished by local interneurons between TI_As and leg motor neurons.     

Biogenic amines modulate synaptic transmission between identified giant interneurons and thoracic interneurons in the escape system of the cockroach

In the escape system of the cockroach, Periplaneta americana, a population of uniquely identifiable throacic interneurons (type A or TI_As) receive information about wind via chemical synapses from a population of ventral giant interneurons (vGIs). The TI_As are involved in the integration of sensory information necessary for orienting the animal during escape. It is likely that there are times in an animal's life when it is advantageous to modify the effectiveness of synaptic transmission between the vGIs and the TI_As. Given the central position of the TI_As inthe escape system, this would greatly alter associated motor outputs. We tested the ability of octopamine, serotonin, and dopamine to modulate synaptic transmission between vGIs and TI_As. Both octopamine and dopamine significantly increased the amplitude of vGI-evoked excitatory postsynaptic potentials (EPSPs) in TI_As at 10^?4?10^?2 M, and 10^?3 M, respectively. On the other hand, serotonin significantly decreased the vGI-evoked EPSPs in TI_As at 10^?4?10^?3 M. These results indicate that octopamine, serotonin, and dopamine are capable of modulating the efficacy of transmission of important neural connections within this circuit. © 1992 John Wiley & Sons, Inc.     

The organization of plurisegmental mechanosensitive interneurons in the central nervous system of the wandering spider Cupiennius salei

Summary In spiders the bulk of the central nervous system (CNS) consists of fused segmental ganglia traversed by longitudinal tracts, which have precise relationships with sensory neuropils and which contain the fibers of large plurisegmental interneurons. The responses of these interneurons to various mechanical stimuli were studied electrophysiologically, and their unilateral or bilateral structure was revealed by intracellular staining. Unilateral interneurons visit all the neuromeres on one side of the CNS. They receive mechanosensory input either from a single leg or from all ipsilateral legs via sensory neurons that invade leg neuromeres and project into specific longitudinal tracts. The anatomical organization of unilateral interneurons suggests that their axons impart their information to all ipsilateral leg neuromeres. Bilateral interneurons are of two kinds, symmetric and asymmetric neurons. The latter respond to stimulation of all legs on one side of the body, having their dendrites amongst sensory tracts of the same side of the CNS. Anatomical evidence suggests that their terminals invade all four contralateral leg neuromeres. Bilaterally symmetrical plurisegmental interneurons have dendritic arborizations in both halves of the fused ventral ganglia. They respond to the stimulation of any of the 8 legs. A third class of cells, the ascending neurons have unilateral or bilateral dendritic arborizations in the fused ventral ganglia and show blebbed axons in postero-ventral regions of the brain. Their response characteristics are similar to those of other plurisegmental interneurons. Descending neurons have opposite structural polarity, arising in the brain and terminating in segmental regions of the fused ventral ganglia. Descending neurons show strong responses to visual stimulation. Approximately 50% of all the recorded neurons respond exclusively to stimulation of a single type of mechanoreceptor (either tactile hairs, or trichobothria, or slit sensilla), while the rest respond to stimulation of a variety of sensilla. However, these functional differences are not obviously reflected by the anatomy. The functional significance of plurisegmental interneurons is discussed with respect to sensory convergence and the coordination of motor output to the legs. A comparison between the response properties of certain plurisegmental interneurons and their parent longitudinal tracts suggests that the tracts themselves do not reflect a modality-specific organization.Abbreviations BPI bilateral plurisegmental interneuron - CNS central nervous system - FVG fused ventral ganglia - LT longitudinal tract - PI plurisegmental interneuron - PSTH peristimulus timehistogram - UPI unilateral plurisegmental interneuron     

Evidence that synaptic transmission between giant interneurons and identified thoracic interneurons in the cockroach is cholinergic

In the cockroach, a population of thoracic interneurons (TIs) receives direct inputs from a population of ventral giant interneuons (vGIs). Synaptic potentials in type-A TIs (TI_As) follow vGI action potentials with constant, short latencies at frequencies up to 200 Hz. These connections are important in the integration of directional wind information involved in determining an oriented escape response. The physiological and biochemical properties of these connections that underlie this decision-making process were examined. Injection of hyperpolarizing or depolarizing current into the postsynaptic TI_As resulted in alterations in the amplitude of the postsynaptic potential (PSP) appropriate for a chemical connection. In addition, bathing cells in zero-calcium, high magnesium saline resulted in a gradual decrement of the PSP, and ultimately blocked synaptic transmission, reversibly. Single-cell choline acetyltransferase (ChAT) assays of vGI somata were performed. These assays indicated that the vGIs can synthesize acetylcholine. Further more, the pharmacological specificity of transmission at the vGI to TI_A connections was similar to that previously reported for nicotinic, cholinergic synapses in insects, suggesting that the transmitter released by vGIs at these sypapses is acetylcholine. © 1992 John Wiley & Sons, Inc.     

Cartesian representation of stimulus direction: Parallel processing by two sets of giant interneurons in the cockroach

The cockroachPeriplaneta americana responds to wind puffs by turning away, both on the ground and when flying. While on the ground, the ventral giant interneurons (ventrals) encode the wind direction and specify turn direction, whereas while flying the dorsal giant interneurons (dorsals) appear to do so. We report here on responses of these cells to controlled wind stimuli of different directions. Using improved methods of wind stimulation and of positioning the animal revealed important principles of organization not previously observed.All six cells of largest axonal diameter on each side respond preferentially to ipsilateral winds. One of these cells, previously thought to respond non-directionally (giant interneuron 2), was found to have a restricted directional response (Fig. 3). The organization of directional coding among the ventral giant interneurons is nearly identical to that among the dorsals (Fig. 2). Each group contains, on each side, one cell that responds primarily to wind from the ipsilateral front, another primarily in the ipsilateral rear, and a third responding more broadly to ipsilateral front and rear.These results are discussed in terms of the mechanisms of directional localization by the assembly of giant interneurons.Abbreviations GI giant interneuron - vGI ventral giant interneuron - dGI dorsal giant interneuron - CF 5-carboxyfluorescein - A6 6th abdominal ganglion - TI thoracic interneuron - BED best excitatory direction     

Pedal serotonergic neurons modulate the synaptic input of withdrawal interneurons ofHelix

A group of serotonergic cells, located in the pedal ganglia ofHelix lucorum, modulates synaptic responses of neurons involved in withdrawal behavior. Extracellular or intracellular stimulation of these serotonergic cells leads to facilitation of spike responses to noxious stimuli in the putative command neurons for withdrawal behavior. Noxious tactile stimuli elicit an increase in background spiking frequency in the modulatory neurons and a corresponding increase in stimulus-evoked spike responses in withdrawal interneurons. The serotonergic neurons have processes in the neuropil of the parieto-visceral ganglia complex, consistent with their putative role in modulating the activity of giant parietal interneurons, which send processes to the same neuropil and to the pedal ganglia. The serotonergic cells respond to noxious tactile and chemical stimuli. Although the group as a whole respond to noxious stimuli applied to any part of the body, most cells respond more to ipsilateral than contralateral stimulation, and exhibit differences in receptive areas. Intracellular investigation revealed electrical coupling between serotonergic neurons which could underlie the recruitment of members of the group not responding to a given noxious stimulus.     

Analysis of proprioceptive inputs to DPG interneurons in the cockroach

In this study we report on morphological and physiological analysis of proprioceptive sensory input to thoracic interneurons. Sensory neurons from leg proprioceptors were filled using cobalt chloride. The morphological location of these sensory neurons was compared with that of the DPG interneurons. The interneurons investigated were found to have morphological overlap with the sensory neurons of the specific proprioceptors, suggesting that they have the potential to receive direct input from these proprioceptors. Individual interneurons were recorded intracellularly and identified by intracellular injection of Lucifer Yellow, and the responses of these cells to mechanical stimulation of specific proprioceptors were analyzed. All of the DPG interneurons tested as well as other interneurons receive input from one or more of these proprioceptors. In addition, DPG interneurons have ipsilateral/contralateral biases in their responses to proprioceptors. Paired stimulation of proprioceptors resulted in enhancement or decrement of the response in the interneurons, depending upon which sensory structures were stimulated together. The results of this study show that proprioceptive information is processed by DPG interneurons.     

Wind-activated thoracic interneurons of the cockroach: I. Responses to controlled wind stimulation

The cockroach escape response begins with a turn away from a wind puff such as that generated by an approaching predator. The presence and direction of that wind is detected by hairs on the animal's cerci, and this information is conducted to the thoracic ganglia via two populations of giant interneurons. In the thoracic ganglia, the giant interneurons excite a number of interneurons, at least some of which in turn excite motor neurons that control leg movement. In this paper we examine response properties of various thoracic neurons to wind stimuli originating from different directions. Three sets of thoracic neurons were distinguished on the basis of latency. Type A interneurons had short latencies to wind stimuli (1.3-2.25 ms). Type B interneurons had longer latencies (4-6 ms), and motor neurons had the longest latencies (5.6-17.0 ms). Individual type A interneurons either responded equally to wind from all directions or were biased in their response. Directionality was related to the presence of ventral branches near one or both sides of the midline of the ganglion. Cells with ventral median (VM) branches on either side tended to be omnidirectional or front-rear biased, whereas cells with VM branches on only one side were biased to that side. Although several type B interneurons had strong wind responses and were directionally sensitive, they did not have VM branches. We hypothesize that the presence of VM branches in type A interneurons permits connection with ventral giant interneurons, and this connection accounts for their short latency and directional properties. This hypothesis will be tested in the companion paper.     

Study of role of inhibitory interneurons in mechanisms of regulation of sensory synapses formed by thalamic and cortical inputs on pyramidal cells of the dorsolateral amygdala nucleus

The work deals with study of role of inhibitory interneurons in the process of regulation of sensory currents converging on soma of pyramidal cells of the dorsolateral amygdala nucleus as well as of role of these interneurons in mechanism of regulation of plasticity of amygdala synapses. It has been shown that the part of the spontaneous inhibitory postsynaptic currents recorded on the dorsolateral amygdala pyramidal cells is relatively high and amounts to about a half of the total amount of the recorded events. Analysis of the evoked postsynaptic responses has shown the interneurons to regulate activity and duration of these responses due to the postsynaptic membrane hyperpolarization as a result of activation of GABA_A-receptors. Also studied was role of interneurons in providing mechanisms of the long-term potentiation of the synaptic responses evoked by stimulation of cortical and thalamic inputs. Block of effect of interneurons with help of picrotoxin has been shown to lead to an increase of evoked potentiation of synaptic responses.     

Central organization of common inhibitory motoneurons in the locust: role of afferent signals from leg mechanoreceptors

Intracellular recordings of mesothoracic common inhibitory neurons (CI₁, CI₂ and CI₃) were made while tactile hairs of the middle legs of locusts (Locusta migratoria) were mechanically stimulated. Generally the three common inhibitory neurons were excited by stimulation of tactile hairs on the ventral and dorsal surface of femur and tibia. The response pattern of all three CI neurons was similar suggesting that they work as a functional unit. Touching hairs on the dorsal surface of tibia and tarsus in some cases led to inhibition of CIs. The connection between sensory cells of tactile hairs and common inhibitory neurons is polysynaptic.To identify interneurons which mediate afferent signals, simultaneous intracellular recordings from CIs and interneurons were made. Different spiking interneurons were identified which made excitatory or inhibitory monosynaptic connections with CIs. Interneurons with inhibitory input to CIs belonged to the ventral midline group of spiking local interneurons. Behavioral and electrophysiological results indicate that reflex movements of the leg are accompanied by activity of CI neurons. Further it appears that CI activity is inhibited when reflex movements of the leg are actively suppressed by the animal.Abbreviations CI common inhibitor - IN interneuron - LY Lucifer Yellow     

Dendritic calcium accumulation regulates wind sensitivity via short‐term depression at cercal sensory‐to‐giant interneuron synapses in the cricket

An in vivo Ca²⁺ imaging technique was applied to examine the cellular mechanisms for attenuation of wind sensitivity in the identified primary sensory interneurons in the cricket cercal system. Simultaneous measurement of the cytosolic Ca²⁺ concentration ([Ca²⁺]_i) and membrane potential of a wind‐sensitive giant interneuron (GI) revealed that successive air puffs caused the Ca²⁺ accumulation in dendrites and diminished the wind‐evoked bursting response in the GI. After tetanic stimulation of the presynaptic cercal sensory nerves induced a larger Ca²⁺ accumulation in the GI, the wind‐evoked bursting response was reversibly decreased in its spike number. When hyperpolarizing current injection suppressed the [Ca²⁺]_i elevation during tetanic stimulation, the wind‐evoked EPSPs were not changed. Moreover, after suprathreshold tetanic stimulation to one side of the cercal nerve resulted in Ca²⁺ accumulation in the GI's dendrites, the slope of EPSP evoked by presynaptic stimulation of the other side of the cercal nerve was also attenuated for a few minutes after the [Ca²⁺]_i had returned to the prestimulation level. This short‐term depression at synapses between the cercal sensory neurons and the GI (cercal‐to‐giant synapses) was also induced by a depolarizing current injection, which increased the [Ca²⁺]_i, and buffering of the Ca²⁺ rise with a high concentration of a Ca²⁺ chelator blocked the induction of short‐term depression. These results indicate that the postsynaptic Ca²⁺ accumulation causes short‐term synaptic depression at the cercal‐to‐giant synapses. The dendritic excitability of the GI may contribute to postsynaptic regulation of the wind‐sensitivity via Ca²⁺‐dependent depression. © 2001 John Wiley & Sons, Inc. J Neurobiol 46: 301–313, 2001     

Anatomical and physiological observations on the organization of mechanoreceptors and local interneurons in the central nervous system of the wandering spider Cupiennius salei

Summary In the wandering spider Cupiennius salei, the functional neuroanatomy of leg mechanosensory receptor neurons and interneurons associated with a single leg neumere was investigated by combined intracellular recording and Lucifer yellow ionophoresis. Trichobothria axons that selectively respond to air currents and to low-frequency airborne vibrations have arborizations restricted to ventral regions of the appropriate leg neuromere. Receptor afferents that respond selectively to substrateborne vibrations are distributed ventrally in the corresponding leg neuromere and extend into certain interganglionic tract neuropiles. Golgi impregnation and intracellular dye filling show that local interneurons originate in ventral sensory neuropiles of leg neuromeres and ascend dorsally to terminate amongst dendrites of motor neurons. Local interneurons generally show higher thresholds for vibration stimuli than do receptors. Local interneurons typically receive inputs from one or several types of receptors. Some respond to stimulation of a single leg, others respond to stimulation of several legs on the same side of the body. The functional morphology of the receptor afferents is correlated with known physiological characteristics of slit sensilla and trichobothria. Structure and activity of the local interneurons are compared with analogous interneurons in other arthropods.     

Synaptic responses evoked by tactile stimuli in Purkinje cells in mouse cerebellar cortex Crus II in vivo

Background

Sensory stimuli evoke responses in cerebellar Purkinje cells (PCs) via the mossy fiber-granule cell pathway. However, the properties of synaptic responses evoked by tactile stimulation in cerebellar PCs are unknown. The present study investigated the synaptic responses of PCs in response to an air-puff stimulation on the ipsilateral whisker pad in urethane-anesthetized mice.

Methods and Main Results

Thirty-three PCs were recorded from 48 urethane-anesthetized adult (6–8-week-old) HA/ICR mice by somatic or dendritic patch-clamp recording and pharmacological methods. Tactile stimulation to the ipsilateral whisker pad was delivered by an air-puff through a 12-gauge stainless steel tube connected with a pressurized injection system. Under current-clamp conditions (I = 0), the air-puff stimulation evoked strong inhibitory postsynaptic potentials (IPSPs) in the somata of PCs. Application of SR95531, a specific GABA_A receptor antagonist, blocked IPSPs and revealed stimulation-evoked simple spike firing. Under voltage-clamp conditions, tactile stimulation evoked a sequence of transient inward currents followed by strong outward currents in the somata and dendrites in PCs. Application of SR95531 blocked outward currents and revealed excitatory postsynaptic currents (EPSCs) in somata and a temporal summation of parallel fiber EPSCs in PC dendrites. We also demonstrated that PCs respond to both the onset and offset of the air-puff stimulation.

Conclusions

These findings indicated that tactile stimulation induced asynchronous parallel fiber excitatory inputs onto the dendrites of PCs, and failed to evoke strong EPSCs and spike firing in PCs, but induced the rapid activation of strong GABA_A receptor-mediated inhibitory postsynaptic currents in the somata and dendrites of PCs in the cerebellar cortex Crus II in urethane-anesthetized mice.     

Functional properties of interneurons of the masticatory reflex

Interneurons of the supratrigeminal nucleus, transmitting effects from the sensory and motor branches of the trigeminal nerve to motoneurons of the muscles of mastication were investigated. Two groups of interneurons with different functional connections were found. The first group (A) contains neurons excited during stimulation of the sensory branches and the motor nerve to the digastric muscle (A₁), neurons excited during stimulation of sensory branches and high-threshold afferents of the motor nerve to the masseter muscle (A₂), and neurons excited only by low-threshold afferents of the motor nerve to the masseter muscle (A₃). Neurons of the second group (B) were activated only by sensory fibers of the trigeminal nerve. It is postulated that interneurons of group A transmit inhibitory effects to motoneurons of antagonist muscles of the lower jaw. Group B interneurons participate in the transmission of excitatory influences to motoneurons of the digastric muscle.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 150–157, March–April, 1972.     

Wind-evoked evasive responses in flying cockroaches

1. A standing cockroach (Periplaneta americana) responds to the air displacement made by an approaching predator, by turning away and running. The wind receptors on the cerci, two posterior sensory appendages, excite a group of ventral giant interneurons that mediate this response. While flying, these interneurons remain silent, owing to strong inhibition; however, the dorsal giant interneurons respond strongly to wind. Using behavioral and electromyographic analysis, we sought to determine whether flying cockroaches also turn away from air displacement like that produced by an approaching flying predator; and if so, whether the cerci and dorsal giant interneurons mediate this response.
2. When presented with a wind puff from the side, a flying cockroach carries out a variety of maneuvers that would cause a rapid turn away and perhaps a dive. These are not evoked if the cerci are ablated (Figs. 4, 5, 6).
3. This evasive response appears to be mediated by a circuit separate from that mediating escape when the cockroach is standing (Fig. 7).
4. The dorsal giant interneurons respond during flight in a directional manner that is suited to mediate this behavior (Fig. 8).
5. Recordings of the wind produced by a moving model predator (Fig. 9), together with measurements of the behavioral latency of tethered cockroaches, suggest that the evasive response would begin just milliseconds before a predator actually arrives. However, as explained in the Discussion section, under natural conditions, the evasive response may well begin earlier, and could indeed be useful in escaping from predators.
6. If cockroaches had a wind-mediated yaw-correcting behavior, as locusts have, this could conflict with the wind-evoked escape. In fact, cockroaches show the opposite, yaw-enhancing response, mediated by the cerci, that does not present a conflict with escape (Figs. 10–14).

     

A second cricket cereal sensory system: bristle hairs and the interneurons they activate

Summary A new sensory system, in the abdomen of the cricketAcheta domesticus, is described. It consists of hair-like receptors, which we have called bristles, distributed on the cercus and abdomen. The sensory neurons, innervating bristles of a wide variety of shapes and sizes, project to a common area of the terminal abdominal ganglion. This region is distinct from the area called the cereal glomerulus which receives input from other receptor types.Three interneurons, whose dendrites are located exclusively in the projection area of bristle sensory neurons, are then described. These interneurons respond to tactile stimuli of the cercus and abdomen, but not to infrasound or to body orientation as do previously described interneurons. Based on the anatomical segregation of the afferents and interneurons, as well as the functional distinction from previously described cereal sensory systems, it is becoming clear that the cereal system is a multimodal sensory system.     

Wind-activated thoracic interneurons of the cockroach: II. Patterns of connection from ventral giant interneurons

A number of thoracic interneurons (TIs) have been found to receive inputs from ventral giant interneurons (vGIs). Each of these cells responds to wind with short latency depolarizations. The previous paper described response properties of several TIs to wind stimuli, including those excited by vGIs. The data showed a correlation between the shape of the TI's wind fields and its morphology. The presence of ventral branches located near the midline of the ganglion predicts a strong response to wind on that side. These ventral median (VM) branches are in the proper location to permit overlap with processes from vGIs. Here we describe the patterns of connections between individual vGIs and 13 of the thoracic interneurons located in the meso- and metathoracic ganglia. A correlation was found between the presence of VM branches and excitation by vGIs. TIs were only excited by vGIs on the side(s) on which VM branches exist. However, presence of a VM branch does not imply that all vGIs on that side make connections with the TI. Summation was found between various vGIs that excited each individual thoracic interneuron. In unilateral thoracic interneurons, no sign of inhibition was found from vGIs on the sides opposite that which contained excitatory vGI axons. Neither was there any evidence of inhibition from dorsal giant interneurons. In addition preliminary evidence indicated that left-right homologues do not inhibit one another. Thus, the data suggest that directional wind fields are primarily the result of selective connection from specific vGIs.