Intracellular olfactory response of hippocampal neurons 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.

Intracellular recording in behaving animals

Electrophysiological recordings from behaving animals provide an unparalleled view into the functional role of individual neurons. Intracellular approaches can be especially revealing as they provide information about a neuron's inputs and intrinsic cellular properties, which together determine its spiking output. Recent technical developments have made intracellular recording possible during an ever-increasing range of behaviors in both head-fixed and freely moving animals. These recordings have yielded fundamental insights into the cellular and circuit mechanisms underlying neural activity during natural behaviors in such areas as sensory perception, motor sequence generation, and spatial navigation, forging a direct link between cellular and systems neuroscience.

Representation of odor habituation and timing in the hippocampus

We performed simultaneous single-neuron recordings from the hippocampus and the olfactory bulb of anesthetized, freely breathing rats. Odor response properties of neurons in the olfactory bulb and hippocampus were characterized as firing rate changes or respiration-coupled changes. A panel of five odors was used. The rats had not been exposed to the odors on the panel before the experiment. The olfactory bulb and hippocampal neurons responded to repeated odor presentations in two ways: first, by changes in firing rate, and second, by respiratory tuning changes. Approximately 60% of bulbar neurons, 48% of hippocampal CA1 neurons, and 12% of hippocampal CA3 neurons showed statistically significant responses. None of the odor-responsive neurons in either the bulb or hippocampus responded to all of the odors on the panel. Repeated 10 sec odor stimuli presented at the intervals of 20, 30, 60, 110, and 160 sec were used to analyze the effect of the interval on odor response properties of the recorded neurons. Bulbar neurons were relatively nonselective for odor interval. Hippocampal neurons showed unexpected selectivity for the interval between repeated odor presentations. CA1 and CA3 neurons responded to only one to three of the intervals in the range. On the basis of these findings, we postulate that the hippocampus has the ability to keep track of the time elapsed between consecutive odor stimuli. This may act as a neuronal substrate for habituation and for complex tasks such as odor-guided navigation.

Liposome-mediated gene transfer into human basal cell carcinoma

Direct intralesional injection of DNA encoding interferon-alpha2 (IFN-alpha2) was used in an effort to sustain local protein delivery for the treatment of human basal cell carcinoma (BCC). A novel model to study this malignancy was established by transplantation of human BCC tissue on to immunodeficient mice with a relatively high rate of engraftment and stable phenotype for superficial BCC (20 of 25; 80%). Gene transfer was significantly increased by using DNA liposome complexes (lipoplexes). Recombinant gene expression was detected predominantly in the epidermis and, to a lesser extent, in the dermis. Gene transfer of IFN-alpha2 using this method resulted in sustained production of IFN-alpha2 protein and increased expression of a known IFN-inducible gene, the class II major histocompatibility (MHC) antigen, and induced BCC regression, presumably through a non-immune mechanism. Intralesional injection of DNA lipoplexes encoding IFN-alpha protein may therefore be applicable to the treatment of cutaneous BCC.

Vagal elicitation of respiratory-type and other unit responses in basal limbic structures of squirrel monkeys

Basal limbic structures (insula, amygdala, hippocampus and surrounding areas) were explored for unit responses to vagal volleys in awake, sitting, squirrel monkeys. Triple shocks were applied every 4 sec to the left cervical vagus nerve. As a control for adventitious activation by extravagal somatic afferents, units responsive to vagal volleys were also tested during shock-induced facial and cervical twitches. Under the given conditions, 16% of a population of more than 200 limbic units responded only to vagal volleys. The ratio of initially excited to initially inhibited units was about 2:3. The response latencies were indicative of both rapidly and slowly conducting, afferent pathways. The entrainment of respiration by vagal volleys revealed that 6% of the tested units discharged with a periodicity commensurate with the respiratory rhythm. Such respiratory units were found in the anterior amygdala, insula and hippocampus. In the case of the hippocampus it can be concluded that the discharge of respiratory-type units is not dependent on olfactory inputs. In the amygdala, the highest percentage of responsive units was found in the central nucleus; none were of a respiratory-type. The particular interest of the respiratory-type units found in this and the preceding study is discussed.

Intracellular synaptic potentials of primate motor cortex neurons during voluntary movement

An intracellular recording technique was applied to the precentral motor cortex of the unanesthetized, chronically behaving monkey. Postsynaptic potentials, responsible for an initiation of the voluntary movement, were recorded. In total, 22 pyramidal tract neurons (PTNs) and 40 non-pyramidal tract neurons (non-PTNs) were successfully penetrated in 5 monkeys while the monkey was performing a flexion-extension wrist movement after a visual cue (reaction time, 200--350 msec). The neurons showed a negative membrane potential shift of at least 30 mV for more than 30 sec. A slowly rising PSP appeared 80--180 msec after the visual cue, and was 70--180 msec prior to an onset of the movement. Spike activities were superimposed upon this slow PSP with 20--80 msec rise time and 2--6 mV depolarization (8 PTNs and 6 non-PTNs). Since these depolarizations were variable in magnitude and latency, these were considered to be summated potentials of small EPSPs and hidden IPSPs. Membrane resistance was measured from an IR drop by a hyperpolarizing current (1.2 X 10(-9) A) passed through a recording electrode, and was 3.5 +/- 1.7 Momega in 18 PTNs and 4.5 +/- 2.5 Momega in 28 non-PTNs. There was a linear relationship in PTNs between membrane resistance and antidromic latency from the pontine pyramid. Because of the time course of PSPs, their possible dendritic origins were discussed.