Activation of single neurons in the rat nucleus accumbens during self- stimulation of the ventral tegmental area

Abstract

Single neurons (n = 76) were recorded in the nucleus accumbens septi (NAS) of rats self-stimulating the ipsilateral medial forebrain bundle (MFB) at the level of the ventral tegmental area (VTA). Responses evoked by rewarding trains of stimulus pulses fell into five categories. The first category (40% of the sample) was characterized by a single discharge at invariant latency in response to individual pulses of the train, and hence was termed "tightly time locked" (TTL). Two TTL neurons were collision tested, and both showed collision, suggesting that self-stimulation of the VTA may involve antidromic, and thus direct, activation of a substantial number of NAS axons. The second category (26%) was characterized by discharges that varied in latency from pulse to pulse and hence was termed "loosely time locked" (LTL). Responses of the remainder of the sample showed no coupling to individual pulses but were categorized based on general firing patterns during the train: excited (7%), inhibited (4%), and no change (23%). Irrespective of category, immediately after the self-stimulation session, the likelihood of evoked discharge at monosynaptic latency by single pulse stimulation of the ipsilateral fimbria was reduced (relative to pre-session level), concurrent with elevations in mean firing rate and motor activity. NAS neurons thus exhibit vigorous activation, apparently both antidromically and orthodromically, in response to VTA self-stimulation. The responses of certain LTL and TTL neurons increased as a function of pulse number in the train, suggestive of integrative mechanisms important for brain stimulation reward. Conduction velocities of directly activated (TTL) axons (0.41-0.65 m/sec) were slower than those previously reported for first-stage, reward-relevant axons. Nonetheless, an implication of direct activation of NAS (and other MFB) axons is that rewarding stimulation triggers action potentials that could invade all axonal branches, including those between the stimulation site and the soma, and send synaptic signals to target neurons. Such signals from NAS neurons could contribute to the increased motor behavior accompanying MFB self-stimulation, and/or could interact with dopamine-mediated signals projected to the NAS from reward circuitry.

Behavioral associations of neuronal activity in the ventral tegmental area of the rat

“…Other NA neurons, however, showed cocaine infusion-related decreases. Wolske et al (1993) recording from NA neurons during intracranial selfstimulation of the medial forebrain bundle, also observed both excitatory and inhibitory responses to stimulation. Thus, the timing of event-related changes in neural activity appears to be more informative than the direction of these changes.…”

Simultaneous dopamine and single-unit recordings reveal accumbens GABAergic responses: Implications for intracranial self-stimulation

“…6; F 2,41 ϭ 5.5; P Յ 0.05) lasting 3.4 Ϯ 0.4 s. Peak firing rate for E-type cells was significantly higher than the rebound excitation elicited by I͞E cells (Table 1; t ϭ Ϫ7.1; P Յ 0.05). However, many E-type units (64.2%) were antidromically driven (11,29) by the short electrical stimulation as evidenced by their short and invariant latency to fire (16.7 Ϯ 0.04 ms) after each stimulus pulse (Fig. 6).…”

“…In this paradigm, animals lever press to deliver electrical stimulation to select brain regions. Like natural rewards, ICS causes time-locked changes in unit activity in the NAc (11,12).…”

Building An Open-source Robotic Stereotaxic Instrument

“…Stereotactic rodent surgery is used in a wide variety of neuroscience applications, including lesioning 1 , iontophoresis 2 , microwire implantation 3 , stimulation 4 , and thin skull imaging 5 . However, there are major hurdles facing those who wish to apply these techniques, including the steep learning curve for performing accurate stereotactic surgery and the high probability of human error.…”

“…Keep the PTFE washers in place on the arm (Figure 3). 4. Screw the threaded end of the collars onto the threaded rods of the stereotaxic instrument's arms (Figure 3).…”