Fornix and fifth-nerve interaction on thalamic units in awake, sitting squirrel monkeys

Intracellular neuronal recording in awake nonhuman primates

Intracellular neuronal recordings from the brain of awake nonhuman primates have remained difficult to obtain because of several formidable technical challenges, such as poor recording stability and difficulties in maintaining long-term recording conditions. We have developed a technique to record neuronal activity by using a coaxial guide tube and sharp electrode assembly, which allows researchers to repeatedly and reliably perform intracellular recordings in the cortex of awake marmosets. Recordings from individual neurons last from several minutes to more than an hour. A key advantage of this approach is that it does not require dura removal, permitting recordings over weeks and months in a single animal. This protocol describes the step-by-step procedures for construction of a custom-made marmoset chair, head-cap implantation, preparation of the sharp electrode and guide tube, neuronal recording and data analysis. As the technique is practical and easy to adapt, we anticipate that it can also be applied to other mammalian models, including larger-size nonhuman primates.

Projections of nucleus caudalis and spinal cord to brainstem and diencephalon in the hedgehog (Erinaceus europaeus and Paraechinus aethiopicus): a degeneration study

In the light of hypotheses related to the evolution of pain-carrying systems in mammals, terminal projection fields in brainstem and diencephalon of efferents of nucleus caudalis (NC) of the spinal trigeminal complex and spinal cord were determined in hedgehog by using Nauta-Gygax and Fink-Heimer silver techniques for degeneration. Unilateral NC lesions resulted in medullary degeneration in the ventral portion of NC contralaterally and bilaterally in cuneate nucleus (CU) and reticular formation. Pontine degeneration was noted ipsilaterally in medial (PBM) and lateral (PBL) parabrachial, facial motor (VII), and interpolar, oral, and main sensory trigeminal nuclei; degeneration in reticular formation was bilateral. Midbrain degeneration was seen bilaterally in caudal superior colliculus (SC), inferior colliculus (IC), periaqueductal gray, and tegmentum. In thalamus, projections to ventroposterior nucleus (VP) were contralateral and concentrated in a crescent extending along the lateral one-third-to-one-half and ventral border of the nucleus. Bilateral degeneration fields were noted in a dorsomedial sector of the "ventral nuclear field," posterior complex (PO), and mediodorsal nucleus (MD), the degeneration always heavier contralaterally in these nuclei. Sparse degeneration was noted in the medial most portions of the medial geniculate nuclei bordering PO and VP. In rostral diencephalon, bilateral degeneration was traced from the inferior thalamic peduncle to the lateral hypothalamic area (LH). Unilateral spinal cord lesions made between C7 and T1 vertebrae resulted in medullary degeneration in NC contralaterally, ipsilaterally in CU and lateral cuneate nucleus, and bilaterally in gracile nucleus, inferior olivary complex, and reticular formation. Pontine degeneration was limited to ipsilateral PBL and bilaterally to VII. Midbrain degeneration was found bilaterally in IC, SC, nucleus sagulum, and tegmentum; a minor projection was noted in interpeduncular nucleus. In thalamus, projections were confined to ipsilateral PO and zona incerta. In rostral diencephalon bilateral fields were noted in LH. NC terminations in PO and VP parallel results of research in hedgehogs on thalamic projections of the dorsal column nuclei (Jane and Schroeder, '71), and particularly the location in VP of most cells responsive to stimulation of the face (Erickson et al., '67). This suggests that somatic input from NC, some of which may be pain-specific, reaches thalamic areas, a portion of whose neurons are characterized as polymodal and at least partially convergent for somatotopy. These results are consistent with the thesis that specific sensory thalamic nuclei evolved from a diffuse sensory region. Response properties of neurons in the dorsomedial portion of the ventral nuclear field, an area which are also received NC efferents, are not known. Last, NC projections to MD and LH implicate the role of "limbic" aspects of nociception.

Reformulation of the Papez circuit: absence of hippocampal influence on cingulate cortex unit activity in the primate

Cingulate cortex (CC) unit responses to hippocampal volleys and afterdischarges were studied in 4 awake unsedated squirrel monkeys using extracellular microelectrodes. Stimuli were delivered via bipolar electrodes chronically implanted bilaterally in anterior and posterior hippocampus. A total of 412 units in 21 tracks were studied and tested to single and multiple shock stimulation. Spontaneous firing rates were approximately equally distributed among slow (0.25 spikes/s), medium (2.5-10), and fast (10-25). Only 2% of cingulate units (9/412) responded orthodromically to hippocampal stimulation: 5 with initial excitation; 4 with initial inhibition. Eight responses had initial latencies from 100-200 ms; one unit a latency of 25 ms. Three units displayed periodic, almost cyclical, excitation. All unit response thresholds were 1 shock, 0.25 mA or less. Hippocampal afterdischarge activity influenced the firing pattern of 17 units: 16 showed intraictal excitation and 1 inhibition. In comparison with the preceding studies in the same model these results indicate that the influence of hippocampal stimulation on cingulate cortex is not nearly as prominent as either the fornix or non-fornix hippocampal influence on hypothalamic, preoptic, and basal forebrain structures. It is proposed that the cingulate cortex is not a prominent link in the Papez circuit.

Supraspinal influences on nociceptive flexion reflex and pain sensation in man

The sensation of pain and the nociceptive flexion reflex of the biceps femoris muscle (RIII, Bi) elicited by electrical stimulation of the ipsilateral sural nerve were studied in human during 4 conditions: (1) a mental task; (2) a stress; (3) during noxious stimulation of the contralateral ulnar nerve; (4) after an intense noxious stimulation of the sural nerve itself. An inhibition of both pain sensation and RIII, Bi was observed in (1), while a facilitation of these parameters was noted in (2). In contrast, no change in RIII, Bi occurred in (3) while the pain sensation was inhibited. In (4), just after the noxious stimulation, there was a marked facilitation of RIII, Bi associated with increased pain sensation. However, 10--12 sec later, the pain sensation returned to its control values, while the RIII, Bi reflex was still facilitated. The latter recovered to its control values 28--30 sec later. These results show the possibility of a dissociation between afferent ascending nociceptive messages and nociceptive motor activity (in 3 and 4). They suggest that supraspinal descending influences can act differently on spinal dorsal horn neurons in the case of pain ascending volleys, and in the case of spinal nociceptive motor activity.

Characterization of electrophysiological properties of intracellularly recorded neurons in the neocortex of awake cats: a comparison of the response to injected current in spike overshoot and undershoot neurons

Intracellular recordings were obtained from 212 neurons of the coronal pericruciate cortex of 7 awake, untrained cats. Glass microelectrodes, filled with K+ citrate alone or K+ citrate with either cyclic GMP or 5'-GMP were used for recording and for injecting steady depolarizing and hyperpolarizing currents intracellularly. The effects of rectangular linearly rising (ramp) current pulses were also studied. Results were compared in spike overshoot* versus undershoot recordings. Spike overshoot recordings had action potentials (APs) larger than associated baseline shifts on penetration; undershoot recordings had APs smaller than associated baseline shifts on penetration. Undershoot recordings are more commonly encountered in mammalian neocortex than are overshoot recordings. (1) Except for sizes and slopes of APs and other effects consistent with the penetration of passive dendritic cables remote from regions of active spike initiation or propagation, no differences in response to current injection or in other electrophysiological properties were found between overshoot and undershoot recordings. (2) Injection of depolarizing currents produced de-reases in the amplitudes of APs, decreased rates of rise and fall of APs and increased frequencies of AP discharge. Injection of hyperpolarizing current produced slowing or cessation of AP discharge with little or only slight increases in AP amplitude when the resting potential was greater than 47 mV. (3) An effectively linear relationship was found between changes in AP size and the magnitude of weak injection depolarizing currents. This relationship provides a basis for measuring changes in cortical neuronal input resistance by the differential spike height method. (4) Most neurons showed little or no accommodative response to the injection of linearly rising, depolarizing currents. Simple or ceiling threshold-latency curves rather than minimal gradient curves were obtained in 83% of the cells in which ramp currents were injected. (5) Modal values of resting potentials between 47 and 53 mV, without increased rates of spontaneous discharge, indicate that most cells have a critical firing threshold near that reported for somatodendritic (SD) rather than initial segment (IS) generated spikes. The evidence suggests that undershoot recordings primarily reflect penetrations of passive dendritic regions rather than functional modification of neurocellular properties as a consequence of impalement.

Effects of vagal volleys on units of intralaminar and juxtalaminar thalamic nuclei in monkeys

As part of an attempt to clarify the nature of inputs to the limbic cortex, the thalamic intralaminar and juxtalaminar nuclei were explored for unit responses to vagal volleys in awake, sitting squirrel monkeys. Vagal shocks elicited responses of a large percentage of units in the anterior medial, paracentral, lateral dorsal, and lateral, and medial dorsal nuclei, as well as in part of the ventral lateral nucleus adjacent to the paracentral. Responsive units showed either initial excitation or initial inhibition. As in the preceding study on the cingulate and supracingulate cortex, there were two main types of initially excited units: type 1 responded with a discharge of 1-3 spikes at relatively short and constant latencies, while type 2 units were characterized by a burst of 3-14 spikes at longer and more variable latencies. Although the findings were compatible with the hypothesis that the anterior and paracentral nuclei transmit vagal impulses to the cingulate and supracingulate cortex, an analysis of latencies suggested that a more rapidly conducting pathway(s) accounts for latencies as short as 12 msec of some cingulate units. Twenty-eight percent of 367 units in the medial dorsal nucleus responded to vagal volleys. This finding gives substantial support to the traditional view that the medial dorsal nucleus transmits interoceptive information to limbic and neocortical areas of the orbitofrontal region.

Regional properties of dorsal and ventral hippocampus in suppression of intralaminar thalamic unit responses

In chloralose-anaesthetized, Flaxedil-paralysed cats, the suppression of extra-lemniscal thalamic units by dorsal and ventral hippocampus was investigated. Unitary responses to test somatic stimuli, recorded in centrolateral and neighbouring thalamic nuclei, were interacted with conditioning electric stimulation in different regions around the hippocampal arch, including parahippocampal gyrus (entorhinal and retrosplenial areas). Stimulation of dorsal (dhc) and ventral (VHC) hippocampus suppressed roughly equal proportions of responses. However, within each of DHC and VHC, effectiveness depended on the region stimulated. In DHC, fields CA1 and CA3, subiculum (SUB), and retrosplenial area, but not field CA4 or dentate gyrus, usually suppressed extralemniscal units at currents below 1.0 mA. In VHC, the most effective regions were entorhinal cortex, CA3, and CA4 with dentate gryus (FD), while stimulation of CA1 or subiculum was almost ineffective, at currents below 1.0 mA. In VHC, the regions were ranked for effectiveness: Entorhinal cortex=CA3 is greater than FD is greater than SUB is greater than CA1. No topographic relationship was found between hippocampal region and thalamic loci for unit suppression. Lemniscal-type unit responses in ventrobasal thalamus were unaffected by stimulation of the hippocampus or parahippocampal gryus. Interruption of the fornix-fimbria system prevented suppression elicited from CA1 of DHC, or from CA3 but not FD of VHC. It had no effect on suppression elicited from retrosplenial or entorhinal cortex. Hippocampal regional variation of effectiveness in suppressing extralemniscal pathways may contribute to the differential behavioural involvements reported for different hippocampal structures.