John T. Hackett

The Role of the Mauthner Cell in Fast-Starts Involving Escape in Teleost Fishes

The commonly observed “tailflip” startle response is one of the most characteristic behavior patterns of bony and cartilagenous fishes and amphibians. In the most familiar example, the behavior pattern is readily elicited in fish following a tap on the side of their aquarium. However, data from behavioral studies show that the response is an effective escape movement that enables the animal to avoid sudden attacks by predators. An example of this is shown in Figure 1 in which a small cyprinid fish uses a common startle response movement pattern to avoid a strike by a piscivorous snake.

Calcium rather than cyclic AMP as the physiological intracellular regulator of prolactin release.

Studies on the mechanisms which govern the release of prolactin were undertaken using two in vitro techniques. A dispersed preparation of rat anterior pituitary cells was made by mechanical means in t

Reticulospinal pacemaker neurons of the rat rostral ventrolateral medulla with putative sympathoexcitatory function: an intracellular study in vitro

Extra- and intracellular recordings of tonically active neurons were obtained in slices of the rat rostral ventrolateral medulla maintained at 31 degrees C. The predominant type consisted of cells with a regular non-bursting discharge rate of 9 +/- 0.3 spikes/s (mean +/- S.E.M., n = 84). Intracellular recordings revealed that these neurons (n = 43) exhibited typical pacemaker potentials reset after a single spike, and an input resistance of 138 +/- 10 M omega (n = 21). No excitatory postsynaptic potentials were detected even during hyperpolarization (5-10 mV) which invariably resulted in silencing the cells (n = 28). Eighteen cells were injected intracellularly with Lucifer yellow, and the tissue was subsequently processed for the immunohistochemical detection of the adrenergic marker phenylethanol-amine N-methyltransferase (PNMT). None of the 12 dye-marked cells recovered exhibited any PNMT-like immunoreactivity, but all were surrounded by numerous adrenergic neurons. In 7 rats subjected to intraspinal injections (T3) of rhodamine-tagged microbeads, 4 out of 9 pacemaker cells marked intracellularly with Lucifer yellow were found labeled with the retrograde marker. It is concluded that the rostral ventrolateral medulla contains non-adrenergic reticulospinal cells with intrinsic pacemaker properties. These neurons probably represent a group of sympathoexcitatory cells on which the basal sympathetic tone depends.

Rostral ventrolateral medullary neurons with intrinsic pacemaker properties are not catecholaminergic.

Neurons of the rat rostral ventrolateral medulla with intrinsic pacemaker properties and immediately adjacent silent neurons were recorded in tissue slices, labeled intracellularly with the fluorescent dye Lucifer yellow, and the tissue was subsequently processed for the immunocytochemical detection of the catecholamine-synthesizing enzyme tyrosine-hydroxylase. Forty-five percent (9/20) of the silent neurons were tyrosine hydroxylase-immunoreactive, but none of the pacemaker cells were (0/15). We conclude that the ventrolateral reticular neurons with intrinsic pacemaker properties are not the C1 adrenergic cells.

Neuronal control of swimming behavior: comparison of vertebrate and invertebrate model systems.

Swimming movements in the leech and lamprey are highly analogous, and lack homology. Thus, similarities in mechanisms must arise from convergent evolution rather than from common ancestry. Despite over 40 years of parallel investigations into this annelid and primitive vertebrate, a close comparison of the approaches and results of this research is lacking. The present review evaluates the neural mechanisms underlying swimming in these two animals and describes the many similarities that provide intriguing examples of convergent evolution. Specifically, we discuss swim initiation, maintenance and termination, isolated nervous system preparations, neural-circuitry, central oscillators, intersegmental coupling, phase lags, cycle periods and sensory feedback. Comparative studies between species highlight mechanisms that optimize behavior and allow us a broader understanding of nervous system function.

Regulation of the neuronal nicotinic acetylcholine receptor by Src family tyrosine kinases

Src family kinases (SFKs) are abundant in chromaffin cells that reside in the adrenal medulla and respond to cholinergic stimulation by secreting catecholamines. Our previous work indicated that SFKs regulate acetylcholine- or nicotine-induced secretion, but the site of modulatory action was unclear. Using whole cell recordings, we found that inhibition of SFK tyrosine kinase activity by PP2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo(3,4-d)pyrimidine) treatment or expression of a kinase-defective c-Src reduced the peak amplitude of nicotine-induced currents in chromaffin cells or in human embryonic kidney cells ectopically expressing functional neuronal α3β4α5 acetylcholine receptors (AChRs). Conversely, the phosphotyrosine phosphatase inhibitor, sodium vanadate, or expression of mutationally activated c-Src resulted in enhanced current amplitudes. These results suggest that SFKs and putative phosphotyrosine phosphatases regulate the activity of AChRs by opposing actions. This proposed model was supported further by the findings that SFKs physically associate with the receptor and that the AChR is tyrosine-phosphorylated.

Does the Mauthner cell conform to the criteria of the command neuron concept

The relationship between the Mauthner (M) cell action potential of the bullfrog tadpole and the rapid tail-flip was studied with electrophysiological and video-recording techniques. Single action potentials were elicited in the M-cell by vibratory stimulation or electrical stimulation of the eighth cranial nerve. These impulses were followed by a tail-flip to the side contralateral to the M-soma. Similarly, a tail-flip was produced by direct intracellular stimulation of the M-cell. Hyperpolarization of the M-soma blocked orthodromic action potentials and prevented the tail-flip. Therefore, the M-cell action potential appears to be sufficient and necessary to produce a rapid tail-flip which is associated with a naturally observed startle behavior.

The anuran mauthner cell and its synaptic bed

Abstract We have performed a general study of the premetamorphic anuran Mauthner cell using anatomical techniques. Anatomical findings confirm that, as in other amphibia, the tadpole Mauthner cell possesses a large soma, a principle lateral dendrite, a secondary medial dendrite, and a large decussating, spinally directed axon. Afferent terminals completely cover the surface of the unmyelinated portion of the cell. An unusually dense neuropile of spiral fibers surrounds the initial axon segment. Six general types of afferent contact are found: (1) club endings which establish mixed junctions with the distal lateral dendrite; (2) Grays Type 1 junctions; (3) Grays Type 2 junctions; (4) mixed junctions; (5) spiral fiber endings; (6) a previously unknown type of junction found upon the medial dendrite. Type 1, Type 2, and mixed junctions are dispersed upon the whole receptive surface of the cell excluding the axon hillock and initial segment, where only spiral fiber endings are found. The spiral fibers synapse with the initial segment and with each other. Some of the latter contacts are symmetrical synapses forming presynaptic-to-presynaptic profiles. This Mauthner cell is therefore quite similar to that of the teleost, the major difference being the absence of unmyelinated club endings associated with the axon cap. Electrophysiological recordings reflect this difference in anatomy.

Relay neurons mediate collateral inhibition of the goldfish Mauthner cell

Abstract The relay neurons which excite cranial motoneurons involved in the Mauthner reflex also act to relay the collateral inhibition of the Mauthner cell. An impulse in a single cranial relay neuron (CRN) evokes both the electrically and chemically mediated synaptic inhibition through a disynaptic pathway.

Calcium dependency of excitatory chemical synaptic transmission in the frog cerebellum in vitro.

Chemical synaptic transmission was studied with microelectrode techniques in isolated frog cerebella maintained in vitro. Purkinje cell (PC) EPSPs, elicited by selective monosynaptic electrical stimulation of both the parallel fiber (PF) and climbing fiber (CF) inputs, could be inverted by depolarizing (outward) current injections. Evoked synaptic transmission at both junctions was reduced by lowering the extracellular concentration of calcium ions ([Ca2+]) below 2 mM. Raising [Ca2+] above 2 mM to 8 mM did not further increase synaptic transmission. Mg2+, Sr2+, and Ba2+ did not substitute for Ca2+ in the transmission process.