Exposure of rats to a series of inescapable shocks produced in sequence both an early naltrexone-insensitive and a late naltrexone-reversible analgesic reaction. Activation of the opiate system was necessary and sufficient to produce an analgesic reaction 24 hours later on exposure to a small amount of shock. The amount of inescapable shock which induced naltrexone-reversible analgesia also produced hyperreactivity to morphine 24 hours later.

Third-order auditory neurons in the avian nucleus laminaris (NL) are the first to receive binaural input. In the chick, NL consists of a monolayer of neurons with polarized dendritic arbors oriented dorsally and ventrally. Afferents from second-order neurons in the ipsilateral nucleus magnocellularis (NM) innervate the dorsal dendrites of NL neurons, distributing processes of approximately equal length to NL neurons along an isofrequency band (roughly caudomedial to rostrolateral). Afferents from the contralateral NM innervate the ventral dendrites of NL neurons, distributing collateral branches sequentially as they proceed from caudomedial to rostrolateral along the isofrequency band of neurons. This innervation pattern could be the basis of a “delay line” circuit, as postulated in models of neural networks mediating sound localization. We examined this circuit by analyzing evoked field potentials using a brain slice preparation containing both NL and NM. The results were consistent with the previous anatomical findings. When the ipsilateral auditory nerve or ipsilateral NM was stimulated, there was no consistent variation in the latency of postsynaptic field potentials across the medial-to-lateral extent of NL. In contrast, when the contralateral NM or NM axons in the crossed dorsal cochlear tract were stimulated, a linear increase in the latency of postsynaptic potentials was observed from medial to lateral positions in NL. When stimulation amplitudes for both the ipsilateral and contralateral inputs were adjusted so as to produce little or no postsynaptic field potential, simultaneous bilateral stimulation evoked a pronounced response. Thus, NL neurons can act as “coincidence detectors.” The amplitude of the postsynaptic response was dependent on the relative timing of stimulation of the two inputs. The optimal time difference changed systematically across the medial-to-lateral extent of NL. This system of delay lines and coincidence detectors could provide a mechanism for converting interaural time differences into a “place map” within NL.

Rats were given series of escapable shocks, identical inescapable shocks, or no shock. The subjects were reexposed to a small amount of shock 24 hours later, after which an in vitro measure of the cellular immune response was examined. Lymphocyte proliferation in response to the mitogens phytohemagglutinin and concanavalin A was suppressed in the inescapable shock group but not in the escapable shock group. This suggests that the controllability of stressors is critical in modulating immune functioning.

The nucleus HVC (proper name) within the avian analog of mammal premotor cortex produces stereotyped instructions through the motor pathway leading to precise, learned vocalization by songbirds. Electrophysiological characterization of component HVC neurons is an important requirement in building a model to understand HVC function. The HVC contains three neural populations: neurons that project to the RA (robust nucleus of arcopallium), neurons that project to Area X (of the avian basal ganglia), and interneurons. These three populations are interconnected with specific patterns of excitatory and inhibitory connectivity, and they fire with characteristic patterns both in vivo and in vitro. We performed whole cell current-clamp recordings on HVC neurons within brain slices to examine their intrinsic firing properties and determine which ionic currents are responsible for their characteristic firing patterns. We also developed conductance-based models for the different neurons and calibrated the models using data from our brain slice work. These models were then used to generate predictions about the makeup of the ionic currents that are responsible for the different responses to stimuli. These predictions were then tested and verified in the slice using pharmacological manipulations. The model and the slice work highlight roles of a hyperpolarization-activated inward current (Ih), a low-threshold T-type Ca(2+) current (ICa-T), an A-type K(+) current (IA), a Ca(2+)-activated K(+) current (ISK), and a Na(+)-dependent K(+) current (IKNa) in driving the characteristic neural patterns observed in the three HVC neuronal populations. The result is an improved characterization of the HVC neurons responsible for song production in the songbird.

We have reviewed a series of experiments which begin to examine the cellular events underlying afferent regulation of neuronal structure. Our initial interest in such experiments stemmed from a desire to understand the cellular nature of experiential influences on brain development. While this remains a long-range goal, it's elusive nature has become increasingly apparent; how will we know when such a goal is achieved? On the other hand, it has become increasingly clear that by approaching this question as a subset of the larger problem of tissue interactions regulating nervous system structure and function, some progress is possible. In this respect, understanding afferent regulation is part and parcel of understanding "competition." Both exemplify the fact that we are dealing with a dynamic system, where changes in the balance of extracellular factors result in a cascade of events defining a new "steady state." Unfortunately, most of our methods are limited to taking "snap-shots" of a few parameters and attempting to reconstruct an epic. Our analyses of the postsynaptic events following cochlea removal have only scratched the surface. They are beginning to reveal myriad cellular processes that are dramatically altered by changing the balance of synaptic activity, or "synaptic drive," in a neuronal system. We have been continually struck by the rapidity of these postsynaptic changes when the manipulations are performed on immature animals. While the kinetics of metabolic and structural events we have studied do not yet match those of ionic events involved in information transmission, the two classes of intercellular communication are coming much closer. Some neuromodulators can alter synaptic currents for up to many seconds, and we have shown that altering afferent activity can cause changes in protein synthesis within a few minutes. The merging of these two classes of phenomena should come as no surprise since our studies and many others have definitively linked a variety of metabolic and structural events to changes in the synaptic drive between two neurons. On the other hand, this progress does highlight the need for increased attention to the short-term changes following manipulations of afferent activity. Hopefully such studies will lead to an understanding of the intracellular chain of events responsible for the regulation of neuronal form. A second area of interest has been the age restrictions on the events we have studied.(ABSTRACT TRUNCATED AT 400 WORDS)