Biomedical subjects

P P Rompre

Publications and source records attributed to P P Rompre.

4 recordsLinked to original sources

PubMed1993

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

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.

Animals↗

PubMed1989

Brain dopamine and reward.

While the evidence is strong that dopamine plays some fundamental and special role in the rewarding effects of brain stimulation, psychomotor stimulants, opiates, and food, the exact nature of that role is not clear. One thing is clear: Dopamine is not the only reward transmitter, and dopaminergic neurons are not the final common path for all rewards. Dopamine antagonists and lesions of the dopamine systems appear to spare the rewarding effects of nucleus accumbens and frontal cortex brain stimulation (Simon et al 1979) and certainly spare the rewarding effects of apomorphine (Roberts & Vickers 1988). It is clear that reward circuitry is multisynaptic, and since dopamine cells do not send axons to each other or receive axons from each other, dopamine can at best serve as but a single link in this circuitry. If dopamine is not a final common path for all rewards, could it be an intermediate common path for most rewards? Some workers have argued against such a view, but at present they must do so on incomplete evidence. For example, Phillips (1984) has argued that there must be multiple reward systems, functionally independent and organized in parallel with one another. His primary evidence, however, is the fact that brain stimulation is rewarding at different levels of the nervous system. As we have seen in the case of midline mesencephalic stimulation, the location of the electrode tip in relation to the dopamine cells and fibers tells us little about the role of dopamine in brain stimulation reward. It seems clear that the ventral tegmental dopamine system plays a critical role in midline mesencephalic reward, despite the distance from the electrode tip to the dopamine cells where morphine causes its dopamine-dependent facilitory effects or to the dopamine terminals where low-dose neuroleptics presumably cause theirs. Until pharmacological challenge has been extended to the cases discussed by Phillips, we can only speculate as to the role of dopamine in each of those cases. In the cases where pharmacological challenge has been examined, only nucleus accumbens and frontal cortex have been found to have dopamine-independent reward sites. It is not consistent with the dopamine hypothesis that dopamine-independent reward sites should exist in these areas, since any reward signals carried to nucleus accumbens or frontal cortex by dopamine fibers would-unless we are to believe that reward "happens" at these sites-have to be carried to the next stage of the circuit by nondopaminergic fibers (there are no dopaminergic cell bodies in any of the dopamine terminal areas).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1986

The curve-shift paradigm in self-stimulation.

Eleven rats were trained to press a lever in an operant chamber in order to earn rewarding trains of cathodal rectangular pulses of fixed intensity and variable frequency. The rate-frequency functions were examined under administration of two neuroleptics (pimozide and chlorpromazine) and three manipulations that interfered with bar pressing (muscular relaxation with methocarbamol, increased lever weight, and limitation of maximum response rates by an F1 reinforcement schedule). Chlorpromazine, and pimozide at low dosages produced a near parallel shift of the rate-frequency functions on the logarithmic axis of pulses, suggesting that these drugs decreased the reinforcing efficacy of the stimulation. The three conditions that interfered with bar-pressing decreased the asymptotic rates and produced small or moderate lateral shifts. Changes in the reinforcing efficacy of the stimulation following the above manipulations were inferred from the shift in the number of pulses required at zero and half-maximal performance (theta 0 and M50 indices, respectively). In the cases of the manipulations that interfered with bar-pressing, M50 indicated a larger artifactual change in the efficacy of the stimulation, compared to theta 0. This phenomenon was mainly due to the fact that the asymptote of the altered functions was shifted towards higher pulse numbers.

Animals↗

PubMed1985

Pontine and mesencephalic substrates of self-stimulation.

Single or twin, moveable monopolar stimulating electrodes were implanted in male adult rats in order to map the medial pons and mesencephalon for self-stimulation behaviour. The electrodes were implanted 6 mm below the surface of the skull and subsequently moved down by steps of 0.13 or 0.16 mm. Each bar press in a Skinner box delivered a train (0.4 s in duration) of cathodal rectangular pulses of fixed intensity (200 microA) and width (0.1 ms). Self-stimulation was recorded from zero to the maximum performance by varying the number of pulses per stimulating train. The rewarding efficacy of the stimulation at each electrode location was inferred from determination of the pulse period corresponding to the threshold and half-maximal performance. Out of 361 mesencephalic and pontine sites sampled, 289 supported self-stimulation. Within the metencephalon, the study revealed a continuous band of positive sites, extending over a dorso-ventral distance of 4 mm, between the floor of the aqueduct and the pontine nuclei. Hence, all electrode locations in the central grey, dorsal raphe and median raphe supported self-stimulation. Within the mesencephalon, the positive band was restricted between the floor of the central grey and the middle part of the interpeduncular nucleus. At the rostral mesencephalon, it shifted laterally towards the substantia nigra. The overlap between the self-stimulation sites and some of the best known ascending and descending pathways is discussed.

Animals↗